Textbook: Chapter 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells
4.1 Comparing Prokaryotic and Eukaryotic Cells: An Overview
Compare the cell structure of prokaryotes and eukaryotes.
Prokaryotes and eukaryotes share fundamental components such as nucleic acids, proteins, lipids, and carbohydrates, and they utilize similar chemical reactions for metabolism. However, they are distinguished primarily by their cell wall structure, ribosomes, and the presence or absence of organelles.
Prokaryotes, in which 99% exist as biofilms, (meaning 'prenucleus') have the following characteristics:
DNA Structure: Typically possess circular, singular chromosomes not enclosed in a membrane. Some, like Gemmata obscuriglobus, have a rare double membrane around their nucleus.
Histones: Their DNA is not associated with histones.
Organelles: Generally lack membrane-bound organelles; any compartments do not have a phospholipid bilayer.
Cell Walls: Almost always contain peptidoglycan.
Cell Division: Usually divide by binary fission, a simpler process than eukaryotic division.
Eukaryotes (meaning 'true nucleus') exhibit different characteristics:
DNA Structure: DNA is located in a nucleus separated from the cytoplasm by a nuclear membrane, existing in multiple linear chromosomes.
Histones: DNA is associated with histones and nonhistone proteins.
Organelles: Contain various membrane-enclosed organelles, such as mitochondria and plastids.
Cell Walls: When present, are chemically simpler than those of prokaryotes.
Cell Division: Typically undergo mitosis, resulting in two identical daughter cells after chromosome replication and division of other organelles.
4.2 The Size, Shape, and Arrangement of Bacterial Cells
Identify the three basic shapes of bacteria.
Most bacteria range from to in diameter and from to in length. They may be a spherical-shaped coccus (plural: cocci, meaning berries), a rod-shaped bacillus (plural: bacilli, meaning little rods or walking sticks), or a spiral.
Cocci: Cocci are typically round but may also be oval, elongated, or flattened. They can remain attached after dividing, forming several groups:
Diplococci: Pairs of cocci
Streptococci: Chainlike patterns of cocci
Tetrads: Groups of four cocci
Sarcinae: Cubelike groups of eight cocci
Staphylococci: Grapelike clusters of cocci These grouping characteristics aid in the identification of certain cocci.
Bacilli: Bacilli divide only across their short axis, leading to fewer groupings than cocci. Most bacilli are single rods (single bacilli). Diplobacilli appear in pairs, and streptobacilli form chains. Some bacilli resemble straws or have tapered ends, while others are oval-shaped and are known as coccobacilli.
Spiral: Spiral bacteria exhibit one or more twists and are never straight. These include:
Vibrios: Curved rod-shaped bacteria.
Spirilla: Helical-shaped bacteria with rigid bodies, similar to corkscrews.
Spirochetes: Helical and flexible bacteria that move with axial filaments contained within a flexible sheath, unlike spirilla, which move using external flagella. Additionally, there are also star-shaped and rectangular prokaryotes.
Most bacteria are monomorphic (maintain single shape). Others, like Rhizobium and Corynebacterium are pleomorphic (they have many shapes).
4.3 Structures External to the Cell Wall
Describe the structure and function of the glycocalyx.
Glycocalyx, meaning "sugar coat," is a term used for substances that surround prokaryotic cells. It is a sticky, gelatinous polymer that sits outside the cell wall, composed of polysaccharide, polypeptide, or both, with chemical composition varying by species. If tightly organized and attached to the cell wall, it's termed a capsule, detectable via negative staining. When loosely attached and unorganized, it's known as a slime layer.
Capsules can enhance bacterial virulence by protecting pathogens from phagocytosis. For instance, the capsule of B. anthracis, made of D-glutamic acid, prevents its destruction during phagocytosis, making it virulent. Similarly, Streptococcus pneumoniae can only cause pneumonia when protected by its polysaccharide capsule; unencapsulated strains are readily phagocytized. The polysaccharide capsule of Klebsiella also aids in preventing phagocytosis while helping the bacterium adhere to and colonize the respiratory tract.
The glycocalyx is crucial for biofilms, aiding attachment as extracellular polymeric substances (EPS) that protect cells and facilitate intercellular communication. This connection enables bacterial survival on diverse surfaces, from rocks and plant roots to human teeth and medical devices. An example, Streptococcus mutans, uses its glycocalyx to attach to teeth and may metabolize it for nutrients in low-energy conditions. Additionally, V. cholerae uses glycocalyx to adhere to small intestine cells. Glycocalyx functions also include protecting cells from dehydration and regulating nutrient movement.
Differentiate flagella, axial filaments, fimbriae, and pili.
Flagella
Flagella are long filamentous appendages the propel bacteria. They can be they may be peritrichous, meaning they are spread across the entire cell, or polar, located at one or both ends of the cell. When polar, flagella can take different forms: monotrichous, with a single flagellum at one end; lophotrichous, featuring a cluster of flagella from one end; or amphitrichous, having flagella at both poles of the cell.
The flagellum has three basic parts:
The filament is the long outermost region and contains a globular protein flagellin arranged in several chains that intertwine and form a helix around a hollow core.
The filament is attached to a slightly wider hook, consisting of a different protein
Third portion is the basal body, which anchors the flagellum to the cell wall and plasma membrane. The basal body is composed of a small central rod inserted into a series of rings. Gram-negative bacteria contain two pairs of rings; the outer pair of rings is anchored to various portions of the cell wall, and the inner pair of rings is anchored to the plasma membrane. In gram-positive bacteria, only the inner pair is present.
The rod and ring help the flagellum rotate.
Motility in bacteria allows movement towards favorable environments or away from adverse ones, a process termed taxis. This movement can be in response to various stimuli, such as chemicals (chemotaxis) and light (phototaxis). Motile bacteria have receptors located in the cytoplasm and plasma membrane that detect stimuli like oxygen, ribose, and galactose. When a positive signal (attractant) is detected, bacteria enhance movement toward the stimulus by executing many runs and few tumbles. Conversely, a negative signal (repellent) increases the frequency of tumbles, leading the bacteria away from the stimulus. The flagellar protein H antigen aids in distinguishing serovars of gram-negative bacteria, with multiple antigens present for organisms like E. coli, some of which are linked to foodborne diseases.
Archaella are like flagella, but use ATP for energy and lack a cytoplasmic core.
Axial Filaments
Spirochetes, two being Treponema pallidum (causes syphilis) and Borreliella burgdorferi (causes Lyme disease), move by axial filaments, or endoflagella, bundles of fibril that arise at the ends of the cell beneath an outer sheath and spiral around cell. Spirochetes are spiral-shaped. Axial filament made of bundle of axial filament called endoflagella. Believed that their spiral shape and movement enables them to more easily penetrate membranes.
Fimbriae and Pili
Gram-negative bacteria possess hairlike appendages known as fimbriae and pili, which are shorter, straighter, and thinner than flagella. These structures are made of a protein called pilin, arranged helically around a central core. Fimbriae can be located at the ends of the bacterial cell or uniformly spread across the surface, with numbers varying from a few to several hundred per cell. They tend to stick to each other and surfaces, playing crucial roles in biofilm formation and adherence to various surfaces like liquids, glass, and rocks. Additionally, fimbriae assist bacteria in attaching to epithelial surfaces within the body. For instance, fimbriae on Neisseria gonorrhoeae help the organism colonize mucous membranes, contributing to disease onset. E. coli's fimbriae also allow attachment to the small intestine lining, resulting in severe watery diarrhea. Absence of fimbriae, due to genetic mutations, prevents colonization and subsequent disease development.
Pili (plural: pili) are longer than fimbriae and are typically present as one or two per bacterial cell. They play roles in motility and DNA transfer. One form of motility, known as twitching motility, involves a pilus extending by adding subunits of pilin, making contact with a surface or another cell, and retracting (powerstroke) as the pilin subunits disassemble. This mechanism is referred to as the grappling hook model of twitching motility, leading to short, jerky movements. Twitching motility has been noted in bacteria such as Pseudomonas aeruginosa, Neisseria gonorrhoeae, and certain E. coli strains. Another type of motility linked to pili is gliding motility, a smooth movement observed in myxobacteria. While the precise mechanism remains largely unknown for most myxobacteria, some use pilus retraction to achieve gliding, enabling travel in low-water environments like biofilms and soil. Additionally, some pili facilitate the gathering of bacteria for DNA transfer, a process known as conjugation. These pili are known as conjugation (sex) pili. During this process, the conjugation pilus of one bacterium, referred to as the donor cell, connects to receptors on another bacterium, whether of the same species or a different one. This contact allows DNA from the donor cell to be transferred, potentially granting new traits to the recipient
4.4 The Cell Wall
The major function of the cell wall is to prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that outside the cell. The cell wall helps maintain its shape and serve as an anchorage point for flagella. The plasma membrane and cell wall increase as the volume of the cell increases. The cell wall is also important to the virulence of some species as well as the site for the action of some antibiotics. The chemical composition of the cell wall helps differentiate major types of bacteria.
The bacterial cell wall is composed of a macromolecular network called peptidoglycan, present alone or with other substances. Peptidoglycan is a protective lattice structure surrounding bacterial cells, composed of repeating disaccharides linked by polypeptides. The disaccharides consist of two monosaccharides: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), which are related to glucose. The difference between the two molecules is a chain along the left side:
The cell wall is composed of alternating NAM and NAG molecules linked in rows of 10-65 sugars to form a carbohydrate backbone (the glycan portion) with adjacent rows linked by polypeptides, which always includes tetrapeptide side chains, which consist of 4 amino acids attached to NAMs in the backbone. The alternating patterns of D and L forms is unique because most amino acids are found as L forms. Parallel tetrapeptide side chains may be linked or directly bonded by a peptide cross-bridge (a short chain of amino acids). Penicillin weakens the bacterial cell wall by interfering with the final linking of peptidoglycan rows through peptide cross-bridges. This disruption leads to cell lysis, which is the destruction caused by the rupture of the plasma membrane and the loss of cytoplasm.
While most bacterial cells will consistently show to be either gram-positive or gram-negative, some gram positive cells show as gram negative in which they are usually dead. However, Bacillus and Clostridium are examples of gram-variable cells.
Compare and contrast the cell walls of gram-positive bacteria, gram-negative bacteria, acid-fast bacteria, archaea, and mycoplasmas. And Compare and contrast archaea and mycoplasmas.
Gram-Positive Bacteria Cell Walls: They consist of many layers of peptidoglycan, forming a thick, rigid structure. Space between cell wall and plasma membrane is periplasmic space which contains the granular layer - composed of lipoteichoic acid. The cell walls also contain teichoic acids, primarily an alcohol and phosphate, which consist of two classes: lipoteichoic acid, which spans peptidoglycan layer and is linked to the membrane, and wall teichoic acid, which is linked to peptidoglycan layer. Because of their negative charge, teichoic acids may bind and regulate movement of cations; assume a role in cell growth, preventing extensive breakdown and cell lysis; and provide much of wall’s antigenic specificity, making it possible to identify. Cell walls of gram-positive streptococci are covered in various polysaccharides that allow them to be grouped into medically significant types. The outer membrane is absent in gram-positive cells.
Gram-Negative Bacteria Cell Walls: They contain on a thin layer of peptidoglycan, which can be one or a few layers and an outer membrane. Peptidoglycan is bonded to lipoproteins in outer membrane and is in periplasm, a gel-like fluid in the periplasmic space of gram-negative bacteria. Periplasm has high concentration of degradative enzymes and transport proteins. Small amount of peptidoglycan makes it more susceptible to mechanical breakage. The outer membrane of gram-negative cells is composed of lipopolysaccharides (LPS), lipoproteins, and phospholipids. It has several functions, including providing a strong negative charge that helps evade phagocytosis and complement action, thus aiding in host defense evasion. The outer membrane serves as a barrier to detergents, heavy metals, bile salts, certain dyes, antibiotics, and digestive enzymes but still allows nutrient passage through porins. LPS consists of three components: lipid A (which acts as an endotoxin upon bacterial death), a core polysaccharide (providing structural stability), and an O polysaccharide (which serves as an antigen used to distinguish serovars of gram-negative bacteria, such as E. coli O157:H7).
Acid Fast Bacteria Cell Wall: Acid-fast bacteria are usually of the genus Mycobacterium and species Nocardia. They have high concentrations (60%) of a hydrophobic waxy lipid (mycolic acid) that prevents dyes from staining. Mycolic acid layer is outside of thin layer of peptidoglycan, both held together by arabinogalactan, a polysaccharide. The waxy cell walls causes cultures to clump and stick to walls of the flask. Acid-fast bacteria can be stained with carbolfuchsin, more effective when heated, which penetrates cell wall, binds to cytoplasm, and resists removal by washing with acid-alcohol. They retain a red color. If mycolic acid layer is removed, they will stain gram-positive.
Archaea Cell Wall: They can lack walls or have walls composed of polysaccharides and proteins that are not peptidoglycan but are similar, pseudomurein. Pseudomurein contains N-acetyltalosaminuronic acid instead of NAM and lacks D-amino acids. Cannot be Gram-stained positive because they lack peptidoglycan.
Mycoplasmas Cell Wall: They are bacteria without a cell wall. They are the smallest and pass through most bacterial filters. Their plasma membrane is unique as it has lipids called sterols, which help protect them from lysis.
Differentiate protoplast, spheroplast, and L form.
Protoplast: Protoplasts occur when the cellular contents remain surrounded by the plasma membrane of gram-positive bacteria do not undergo lysis. Cell walls of gram-positive bacteria can be damaged by exposure to lysozyme. It catalyzes hydrolysis of the bonds between sugars in the repeating disaccharide backbone of peptidoglycan.
Spheroplast: Spheroplasts occur when gram-negative cells first interact with EDTA, weakening the ionic bonds in the outer membrane and damaging it, and then using lysozyme to access the peptidoglycan layer. The wall is not destroyed like gram-positive cells and some of the outer membrane remains.
L form: Cells of the genus Proteus (as well as other genera) that lose their cell walls and swell into irregular shaped cells. May spontaneously form or develop in response to penicillin or lysozyme. Can live and divide repeatedly or even return to the walled state.
Protoplasts, spheroplasts, and L forms will burst in pure water or very dilute salt or sugar solutions, undergoing osmotic lysis.
4.5 Structures Internal to the Cell Wall
Describe the structure, chemistry, and functions of the prokaryotic plasma membrane.
The plasma membrane consists primarily of phospholipids and proteins. They are less rigid due to the lack of sterols, the membrane is less rigid (with exception to Mycoplasma which does have membrane sterols). The bacterial plasma membrane is a phospholipid bilayer, with a polar, hydrophilic head composed of a phosphate group and glycerol and a nonpolar, hydrophobic tail composed of fatty acids.
Proteins in the membrane are arranged as peripheral or integral proteins:
Peripheral Proteins:
Located at the inner or outer surface of the membrane.
Easily removed by mild treatments.
Functions:
Catalyze chemical reactions (enzymes).
Provide structural support (scaffold).
Mediate changes in membrane shape during movement.
Integral Proteins:
Removed only by disrupting the lipid bilayer (using detergents).
Most penetrate the membrane as transmembrane proteins.
Some serve as channels for substance transport.
Glycoproteins and Glycolipids:
Proteins/lipids with carbohydrates attached.
Functions:
Protect and lubricate the cell.
Involved in cell-to-cell interactions.
Example: Some viruses (e.g., influenza) enter cells by binding to glycoproteins.
Fluid Mosaic Model:
The phospholipid and protein molecules move freely within the membrane.
Phospholipids form a self-sealing bilayer in water due to fatty acid tails.
Membrane viscosity is comparable to olive oil, allowing protein movement without damaging the membrane structure.
The plasma membrane’s primary function is selective permeability, which depends on several factors. Larger molecules (proteins) cannot fit through phospholipid bilayer, but smaller molecules like water, oxygen, carbon dioxide, and simple sugars pass easily. Ions penetrate slowly. Nonpolar molecules usually pass through easily. The plasma membrane also contains enzymes to catalyze the breakdown of nutrients and produce ATP. For some bacteria, pigments and enzymes involved with photosynthesis are found in infoldings of plasma membrane that extend into the cytoplasm, called chromatophores. However, the photosynthetic thylakoid membranes of cyanobacteria may be separate from plasma membrane, resembling chloroplasts. Electron microscopes have shown irregular folds called mesosomes, which are speculated to form when the membrane is damaged.
Define simple diffusion, facilitated diffusion, osmosis, active transport, and group translocation.
Simple diffusion: the net overall movement of molecules or ions from an area of high concentration to an area of low concentration, until equilibrium is reached.
Facilitated diffusion: Transporter proteins or permeases in the membrane serve as channels for ions or large molecules without expending energy. These transporters are usually nonspecific and allow a wide variety of ins or molecules. If molecules are too large, the bacteria will release extracellular enzymes to catalyze them into simpler molecules.
Osmosis: This is the process of water moving through the membrane either through simple diffusion or through aquaporins (integral membrane proteins). Through osmosis and osmotic pressure, the bacterial cell can be isotonic (equal pressure), hypotonic (where water is forced into the cell due to higher solute concentration; gram-negative bacteria may burst of undergo osmotic lysis), or hypertonic (the cell has lower concentration of solutes; most bacteria will shrink and collapse, called plasmolyze.)
Active Transport: The cell uses ATP to move substances across plasma membrane like ions (NA⁺, K⁺, H⁺, Ca²⁺, and Cl⁻), amino acids, and simple sugars. While passive processes work, it can help move materials against the concentration gradient. Different transporter for each substance or group of related substances.
Group translocation: Exclusive to prokaryotes where the substance is chemically altered during transport process. Once inside membrane, it is impermeable to it. This helps cells acquire resources even in low concentrations. Requires energy supplied by high-energy phosphate compounds, such as phosphoenolpyruvic acid (PEP). With glucose, a phosphate group is added to the sugar. This phosphorylated form of glucose, which cannot be transported out, can then be used in the cell’s metabolic pathways.
Identify the functions of the nucleoid and ribosomes.
Nucleoid and Plasmids in Bacterial Cells
The nucleoid typically contains a single, long, double-stranded DNA thread called the bacterial chromosome.
This chromosome carries the genetic information necessary for the cell's structures and functions.
Unlike eukaryotic chromosomes, bacterial chromosomes do not have a nuclear envelope and lack histones.
The nucleoid shape can be spherical, elongated, or dumbbell-shaped.
In actively growing bacteria, DNA can occupy about 20% of the cell volume, as it pre-synthesizes for future cells.
The bacterial chromosome is attached to the plasma membrane, which aids in the replication and segregation of chromosomes during cell division.
Bacteria may also contain plasmids, which are small, circular, double-stranded DNA molecules that replicate independently of the bacterial chromosome.
Plasmids are extrachromosomal genetic elements and usually contain 5 to 100 genes that are not essential for survival under normal conditions.
Plasmids can provide advantages, such as antibiotic resistance, tolerance to toxic metals, toxin production, and enzyme synthesis.
Plasmids can be transferred between bacteria and are utilized in biotechnology for gene manipulation.
Ribosomes: All eukaryotic and prokaryotic cells contain ribosomes where protein synthesis occurs. Cells with high rates of protein synthesis have more ribosomes. Prokaryotic cell cytoplasm contains many ribosomes, giving it a granular look. Ribosomes consist of two subunits made of proteins and ribosomal RNA (rRNA). Prokaryotic ribosomes (70S) are smaller and different in composition from eukaryotic ribosomes (80S). The 70S ribosome is made of a 30S subunit (containing 1 rRNA) and a 50S subunit (containing 2 rRNA). The "S" stands for Svedberg units, indicating sedimentation rate based on size, weight, and shape, not a direct sum of the subunits.
Identify the functions of four inclusions.
Inclusions in prokaryotic cells serve as storage or reserve materials and can include:
Metachromatic granules: Also known as volutin, store inorganic phosphate, which can be used in nucleic acid synthesis and ATP production. Stain red with certain blue dyes. grows in phosphate-rich environments. Are a characteristic of Corynebacterium diphtheriae.
Polysaccharide granules: Serve as energy reserves, typically composed of glycogen or starch. Presence is known when in contact with iodine since glycogen appear reddish brown and starch appear blue.
Lipid inclusions: Store lipids as energy reserves, which can be used for cell metabolism. Appear in species of Mycobacterium, Bacillus, Azotobacter, Spirillum, and other genera. Revealed by staining cells with fat-soluble dyes.
Sulfur granules: Serve as energy reserves for certain bacteria that can utilize sulfur for metabolic processes.
Describe the functions of endospores, sporulation, and endospore germination.
Endospores: Specialized resting cells the form from gram-positive bacteria when essential nutrients are depleted. They are highly durable dehydrated cells with the thick walls and additional layers. Can survive extreme heat, lack of water, and exposure to toxic chemicals and radiation. Coxiella burnetii, a gram-negative bacteria can form endospores that cause Q fever. Boiling is not effective.
Sporulation: the several-hour long process for endospores to form within a vegetative cell. Usually form when key nutrient like carbon or nitrogen is scarce. During sporulation, the first observable stage involves the formation of a forespore, created by an ingrowth of the plasma membrane (spore septum) that isolates the replicated bacterial chromosome and a small portion of cytoplasm. This forespore is surrounded by a double-layered membrane. Between these membranes, thick layers of peptidoglycan are deposited, followed by the formation of a protein-rich spore coat that provides resistance to harsh chemicals. Eventually, the original cell degrades, leading to the release of the endospore.
Endospore germination: a means of restarting the bacteria by being triggered from high heat or small triggering molecules, germinants, alanine and inosine.
4.6 Flagella and Cilia
Differentiate prokaryotic and eukaryotic flagella.
Eukaryotic cells have flagella (long in size and few) and cilia (numerous and short) Algae, like Euglena, use flagellum for locomotion while protozoa, like Tetrahymena, use cilia for locomotion. Both consist of nine pairs of microtubules (doublets) arranged in a ring, plus another two microtubules in the center of the ring, an arrangement called a 9 + 2 array. Microtubules are long, hollow tubes made of protein called tubulin.
A prokaryotic flagellum rotates, but eukaryotic flagella move like a wave.
4.7
Compare and contrast prokaryotic and eukaryotic cell walls and glycocalyxes.
Many eukaryotes have simpler cell walls. many algae have cell walls made of cellulose. Fungi have cellulose but most of cell wall is based upon chitin, a polymer of NAG units. Cell walls of yeast contain glucan and mannan. Eukaryotes without a cell wall have a thin membrane but those in contact with the environment may have coatings. Protozoa have an atypical flexible outer protein called a pellicle.
Other eukaryotic cells (animals included) have membrane covered by a glycocalyx, a layer of substantial amounts of sticky carbs. Some carbs are covalently bound to proteins, glycoproteins, and lipids, glycolipids. It helps strengthen cell surface, help attach cells, and enable cell recognition.
4.8 - 4.10
Compare and contrast prokaryotic and eukaryotic plasma membranes.
Eukaryote and prokaryote plasma membranes have different proteins.
Eukaryotic plasma membrane:
Contain carbs which serve as attachment sites for bacteria and receptor sites for cell-to-cell recognition.
Contain sterols to help membranes resist lysis
Eukaryotic cells can perform endocytosis, where material is brought into the cell by having the membrane wrap around it. Three types:
phagocytosis: Cellular projections engulf particles and bring into cell; used by white blood cells.
Pinocytosis: membrane folds inward, bringing extracellular fluid and substances in.
Receptor-mediated endocytosis: substances bind to the receptors and cause the membrane to fold in. It’s a way viruses can enter.
The cytoplasm of eukaryotic cells is the substance found between the plasma membrane and the nucleus, containing various cellular components. The fluid portion of the cytoplasm is referred to as cytosol, while the cytoskeleton consists of microfilaments, intermediate filaments, and microtubules, corresponding to components found in prokaryotes. The eukaryotic cytoskeleton provides structural support, shape, and aids in transporting substances, including movement during phagocytosis. Cytoplasmic streaming refers to the movement of cytoplasm within the cell, facilitating nutrient distribution, whereas important enzymes in prokaryotic cytoplasm are compartmentalized in eukaryotic organelles.
Eukaryotic ribosomes are larger than prokaryotic ribosomes. These eukaryotic ribosomes are S ribosomes, each of which consists of a large S sub unit containing three molecules of rRNA and a smaller S subunit with one molecule of rRNA. They are made in the nucleus. However, prokaryotic ribosomes are made in the cytoplasm.
4.11: Organelles
Define organelle.
A membrane0enclosed structure within eukaryotic cells each with specific functions.
Describe the functions of the nucleus, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes, and centrosomes.
Functions of Organelles in Eukaryotic Cells:
Nucleus: Nucleus has a double membrane, nuclear envelope, that contains nuclear pores to communicate with the cytoplasm. Nucleoli are spherical bodies in nuclear envelope that are condensed regions of chromosomes where ribosomal RNA is synthesized. The nucleus houses most of the cell's DNA, which combines with proteins, including histones and nonhistones, to form nucleosomes. When the cell is not reproducing, this DNA-protein complex appears as chromatin, a threadlike mass. During nuclear division, chromatin condenses into shorter, thicker structures known as chromosomes. Mitosis and Meiosis needed to segregate chromosomes.
Endoplasmic Reticulum: Continuous with the nuclear envelope. Two different forms of ER:
Rough ER: Outer surface studded with ribosomes for protein synthesis. Synthesized proteins enter cisterns in ER for processing and sorting. Sometimes, enzymes attach proteins to carbs to form glycoproteins, and other times attach proteins to phospholipids. Rough ER synthesizes secretory proteins and membrane molecules
Smooth ER: Extends from rough ER to form network of membrane tubules. No ribosomes, but contains enzymes to become more diverse than rough ER. Like ER, it synthesizes phospholipids. Also synthesizes fats and steroids. In liver cells, it helps release glucose in bloodstream and inactivate/detoxify drugs and other harmful substances. Releases calcium ions in muscle cells to trigger contraction process.
Golgi Complex: It’s like the mail service. Proteins synthesized by ribosomes are encased in ER membrane, called a transport vesicle. It fuses with the Golgi complex, releasing into the cisterns. Proteins modified in one cistern and transported to another via transfer vesicles. Enzymes in cisterns form proteins to become glycoproteins, glycolipids, and lipoproteins. Some of processed proteins leave in secretory vesicles to go to plasma membrane to be discharged via exocytosis. Some are transported to become a part of plasma membrane. Finally, some leave in vesicles called storage vesicles.
Lysosomes: Major storage vesicle only in animal cells. Formed from Golgi complexes and only have a single membrane with no internal structure. But, they contain 40 different digestive enzymes to break down various molecules.
Vacuoles: A space or cavity in cell that is enclosed by a membrane called a tonoplast. Plants have much larger vacuoles that take up 5-90% of cell volume. Some serve as temporary storage organelles; others form during endocytosis to bring food in cell. Also store metabolic wastes and poisons. May also take up excessive water.
Mitochondria: POWERHOUSE OF THE CELL. Two membranes. external membrane is smooth but the internal is arranged in a series of folds, mitochondrial cristae. Center of mitochondrion is semifluid substance called mitochondrial matrix. ATP production. Have 70S ribosomes and some DNA of their own.
Chloroplasts: Main source for photosynthesis and has 70S ribosomes. Double membrane-enclosed and contains both the pigment chlorophyll and enzymes for photosynthesis. Chlorophyll contained in flat membranes called thylakoids and thylakoids stacked as grana. Internal fluid of chloroplast is the stroma.
Peroxisomes: Similar to lysosomes but smaller and contain one or more enzymes to break down various organic substances. Most likely for from budding off ER. By-product of molecular breakdown is hydrogen peroxide, which the peroxisomes have catalase to break down hydrogen peroxide.
Centrosomes: Organizes the mitotic spindle for cell division. Near the nucleus in animal cells and has two components:
Pericentriolar matrix: Region of cytosol with dense network of small protein fibers.
Centrioles: Pair of cylindrical structures within pericentriolar matrix. Nine clusters of 3 microtubules in circular pattern and arranged in 9 + 0 array (9 microtubules around and 0 center microtubules). Long axis of one centriole at right angle to other.
4.12 Evolution of Eukaryotic Cells
Discuss evidence that supports the endosymbiotic theory of eukaryotic evolution
Both mitochondria and chloroplasts resemble bacteria in size and shape as well as contain circular DNA. Mitochondrial and chloroplast ribosomes resemble prokaryotes. Same antibiotics that inhibit protein synthesis bacteria inhibit it for mitochondria and chloroplasts.
Textbook: Chapter 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells
4.1 Comparing Prokaryotic and Eukaryotic Cells: An Overview
Compare the cell structure of prokaryotes and eukaryotes.
Prokaryotes and eukaryotes share fundamental components such as nucleic acids, proteins, lipids, and carbohydrates, and they utilize similar chemical reactions for metabolism. However, they are distinguished primarily by their cell wall structure, ribosomes, and the presence or absence of organelles.
Prokaryotes, in which 99% exist as biofilms, (meaning 'prenucleus') have the following characteristics:
DNA Structure: Typically possess circular, singular chromosomes not enclosed in a membrane. Some, like Gemmata obscuriglobus, have a rare double membrane around their nucleus.
Histones: Their DNA is not associated with histones.
Organelles: Generally lack membrane-bound organelles; any compartments do not have a phospholipid bilayer.
Cell Walls: Almost always contain peptidoglycan.
Cell Division: Usually divide by binary fission, a simpler process than eukaryotic division.
Eukaryotes (meaning 'true nucleus') exhibit different characteristics:
DNA Structure: DNA is located in a nucleus separated from the cytoplasm by a nuclear membrane, existing in multiple linear chromosomes.
Histones: DNA is associated with histones and nonhistone proteins.
Organelles: Contain various membrane-enclosed organelles, such as mitochondria and plastids.
Cell Walls: When present, are chemically simpler than those of prokaryotes.
Cell Division: Typically undergo mitosis, resulting in two identical daughter cells after chromosome replication and division of other organelles.
4.2 The Size, Shape, and Arrangement of Bacterial Cells
Identify the three basic shapes of bacteria.
Most bacteria range from to in diameter and from to in length. They may be a spherical-shaped coccus (plural: cocci, meaning berries), a rod-shaped bacillus (plural: bacilli, meaning little rods or walking sticks), or a spiral.
Cocci: Cocci are typically round but may also be oval, elongated, or flattened. They can remain attached after dividing, forming several groups:
Diplococci: Pairs of cocci
Streptococci: Chainlike patterns of cocci
Tetrads: Groups of four cocci
Sarcinae: Cubelike groups of eight cocci
Staphylococci: Grapelike clusters of cocci These grouping characteristics aid in the identification of certain cocci.
Bacilli: Bacilli divide only across their short axis, leading to fewer groupings than cocci. Most bacilli are single rods (single bacilli). Diplobacilli appear in pairs, and streptobacilli form chains. Some bacilli resemble straws or have tapered ends, while others are oval-shaped and are known as coccobacilli.
Spiral: Spiral bacteria exhibit one or more twists and are never straight. These include:
Vibrios: Curved rod-shaped bacteria.
Spirilla: Helical-shaped bacteria with rigid bodies, similar to corkscrews.
Spirochetes: Helical and flexible bacteria that move with axial filaments contained within a flexible sheath, unlike spirilla, which move using external flagella. Additionally, there are also star-shaped and rectangular prokaryotes.
Most bacteria are monomorphic (maintain single shape). Others, like Rhizobium and Corynebacterium are pleomorphic (they have many shapes).
4.3 Structures External to the Cell Wall
Describe the structure and function of the glycocalyx.
Glycocalyx, meaning "sugar coat," is a term used for substances that surround prokaryotic cells. It is a sticky, gelatinous polymer that sits outside the cell wall, composed of polysaccharide, polypeptide, or both, with chemical composition varying by species. If tightly organized and attached to the cell wall, it's termed a capsule, detectable via negative staining. When loosely attached and unorganized, it's known as a slime layer.
Capsules can enhance bacterial virulence by protecting pathogens from phagocytosis. For instance, the capsule of B. anthracis, made of D-glutamic acid, prevents its destruction during phagocytosis, making it virulent. Similarly, Streptococcus pneumoniae can only cause pneumonia when protected by its polysaccharide capsule; unencapsulated strains are readily phagocytized. The polysaccharide capsule of Klebsiella also aids in preventing phagocytosis while helping the bacterium adhere to and colonize the respiratory tract.
The glycocalyx is crucial for biofilms, aiding attachment as extracellular polymeric substances (EPS) that protect cells and facilitate intercellular communication. This connection enables bacterial survival on diverse surfaces, from rocks and plant roots to human teeth and medical devices. An example, Streptococcus mutans, uses its glycocalyx to attach to teeth and may metabolize it for nutrients in low-energy conditions. Additionally, V. cholerae uses glycocalyx to adhere to small intestine cells. Glycocalyx functions also include protecting cells from dehydration and regulating nutrient movement.
Differentiate flagella, axial filaments, fimbriae, and pili.
Flagella
Flagella are long filamentous appendages the propel bacteria. They can be they may be peritrichous, meaning they are spread across the entire cell, or polar, located at one or both ends of the cell. When polar, flagella can take different forms: monotrichous, with a single flagellum at one end; lophotrichous, featuring a cluster of flagella from one end; or amphitrichous, having flagella at both poles of the cell.
The flagellum has three basic parts:
The filament is the long outermost region and contains a globular protein flagellin arranged in several chains that intertwine and form a helix around a hollow core.
The filament is attached to a slightly wider hook, consisting of a different protein
Third portion is the basal body, which anchors the flagellum to the cell wall and plasma membrane. The basal body is composed of a small central rod inserted into a series of rings. Gram-negative bacteria contain two pairs of rings; the outer pair of rings is anchored to various portions of the cell wall, and the inner pair of rings is anchored to the plasma membrane. In gram-positive bacteria, only the inner pair is present.
The rod and ring help the flagellum rotate.
Motility in bacteria allows movement towards favorable environments or away from adverse ones, a process termed taxis. This movement can be in response to various stimuli, such as chemicals (chemotaxis) and light (phototaxis). Motile bacteria have receptors located in the cytoplasm and plasma membrane that detect stimuli like oxygen, ribose, and galactose. When a positive signal (attractant) is detected, bacteria enhance movement toward the stimulus by executing many runs and few tumbles. Conversely, a negative signal (repellent) increases the frequency of tumbles, leading the bacteria away from the stimulus. The flagellar protein H antigen aids in distinguishing serovars of gram-negative bacteria, with multiple antigens present for organisms like E. coli, some of which are linked to foodborne diseases.
Archaella are like flagella, but use ATP for energy and lack a cytoplasmic core.
Axial Filaments
Spirochetes, two being Treponema pallidum (causes syphilis) and Borreliella burgdorferi (causes Lyme disease), move by axial filaments, or endoflagella, bundles of fibril that arise at the ends of the cell beneath an outer sheath and spiral around cell. Spirochetes are spiral-shaped. Axial filament made of bundle of axial filament called endoflagella. Believed that their spiral shape and movement enables them to more easily penetrate membranes.
Fimbriae and Pili
Gram-negative bacteria possess hairlike appendages known as fimbriae and pili, which are shorter, straighter, and thinner than flagella. These structures are made of a protein called pilin, arranged helically around a central core. Fimbriae can be located at the ends of the bacterial cell or uniformly spread across the surface, with numbers varying from a few to several hundred per cell. They tend to stick to each other and surfaces, playing crucial roles in biofilm formation and adherence to various surfaces like liquids, glass, and rocks. Additionally, fimbriae assist bacteria in attaching to epithelial surfaces within the body. For instance, fimbriae on Neisseria gonorrhoeae help the organism colonize mucous membranes, contributing to disease onset. E. coli's fimbriae also allow attachment to the small intestine lining, resulting in severe watery diarrhea. Absence of fimbriae, due to genetic mutations, prevents colonization and subsequent disease development.
Pili (plural: pili) are longer than fimbriae and are typically present as one or two per bacterial cell. They play roles in motility and DNA transfer. One form of motility, known as twitching motility, involves a pilus extending by adding subunits of pilin, making contact with a surface or another cell, and retracting (powerstroke) as the pilin subunits disassemble. This mechanism is referred to as the grappling hook model of twitching motility, leading to short, jerky movements. Twitching motility has been noted in bacteria such as Pseudomonas aeruginosa, Neisseria gonorrhoeae, and certain E. coli strains. Another type of motility linked to pili is gliding motility, a smooth movement observed in myxobacteria. While the precise mechanism remains largely unknown for most myxobacteria, some use pilus retraction to achieve gliding, enabling travel in low-water environments like biofilms and soil. Additionally, some pili facilitate the gathering of bacteria for DNA transfer, a process known as conjugation. These pili are known as conjugation (sex) pili. During this process, the conjugation pilus of one bacterium, referred to as the donor cell, connects to receptors on another bacterium, whether of the same species or a different one. This contact allows DNA from the donor cell to be transferred, potentially granting new traits to the recipient
4.4 The Cell Wall
The major function of the cell wall is to prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that outside the cell. The cell wall helps maintain its shape and serve as an anchorage point for flagella. The plasma membrane and cell wall increase as the volume of the cell increases. The cell wall is also important to the virulence of some species as well as the site for the action of some antibiotics. The chemical composition of the cell wall helps differentiate major types of bacteria.
The bacterial cell wall is composed of a macromolecular network called peptidoglycan, present alone or with other substances. Peptidoglycan is a protective lattice structure surrounding bacterial cells, composed of repeating disaccharides linked by polypeptides. The disaccharides consist of two monosaccharides: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), which are related to glucose. The difference between the two molecules is a chain along the left side:
The cell wall is composed of alternating NAM and NAG molecules linked in rows of 10-65 sugars to form a carbohydrate backbone (the glycan portion) with adjacent rows linked by polypeptides, which always includes tetrapeptide side chains, which consist of 4 amino acids attached to NAMs in the backbone. The alternating patterns of D and L forms is unique because most amino acids are found as L forms. Parallel tetrapeptide side chains may be linked or directly bonded by a peptide cross-bridge (a short chain of amino acids). Penicillin weakens the bacterial cell wall by interfering with the final linking of peptidoglycan rows through peptide cross-bridges. This disruption leads to cell lysis, which is the destruction caused by the rupture of the plasma membrane and the loss of cytoplasm.
While most bacterial cells will consistently show to be either gram-positive or gram-negative, some gram positive cells show as gram negative in which they are usually dead. However, Bacillus and Clostridium are examples of gram-variable cells.
Compare and contrast the cell walls of gram-positive bacteria, gram-negative bacteria, acid-fast bacteria, archaea, and mycoplasmas. And Compare and contrast archaea and mycoplasmas.
Gram-Positive Bacteria Cell Walls: They consist of many layers of peptidoglycan, forming a thick, rigid structure. Space between cell wall and plasma membrane is periplasmic space which contains the granular layer - composed of lipoteichoic acid. The cell walls also contain teichoic acids, primarily an alcohol and phosphate, which consist of two classes: lipoteichoic acid, which spans peptidoglycan layer and is linked to the membrane, and wall teichoic acid, which is linked to peptidoglycan layer. Because of their negative charge, teichoic acids may bind and regulate movement of cations; assume a role in cell growth, preventing extensive breakdown and cell lysis; and provide much of wall’s antigenic specificity, making it possible to identify. Cell walls of gram-positive streptococci are covered in various polysaccharides that allow them to be grouped into medically significant types. The outer membrane is absent in gram-positive cells.
Gram-Negative Bacteria Cell Walls: They contain on a thin layer of peptidoglycan, which can be one or a few layers and an outer membrane. Peptidoglycan is bonded to lipoproteins in outer membrane and is in periplasm, a gel-like fluid in the periplasmic space of gram-negative bacteria. Periplasm has high concentration of degradative enzymes and transport proteins. Small amount of peptidoglycan makes it more susceptible to mechanical breakage. The outer membrane of gram-negative cells is composed of lipopolysaccharides (LPS), lipoproteins, and phospholipids. It has several functions, including providing a strong negative charge that helps evade phagocytosis and complement action, thus aiding in host defense evasion. The outer membrane serves as a barrier to detergents, heavy metals, bile salts, certain dyes, antibiotics, and digestive enzymes but still allows nutrient passage through porins. LPS consists of three components: lipid A (which acts as an endotoxin upon bacterial death), a core polysaccharide (providing structural stability), and an O polysaccharide (which serves as an antigen used to distinguish serovars of gram-negative bacteria, such as E. coli O157:H7).
Acid Fast Bacteria Cell Wall: Acid-fast bacteria are usually of the genus Mycobacterium and species Nocardia. They have high concentrations (60%) of a hydrophobic waxy lipid (mycolic acid) that prevents dyes from staining. Mycolic acid layer is outside of thin layer of peptidoglycan, both held together by arabinogalactan, a polysaccharide. The waxy cell walls causes cultures to clump and stick to walls of the flask. Acid-fast bacteria can be stained with carbolfuchsin, more effective when heated, which penetrates cell wall, binds to cytoplasm, and resists removal by washing with acid-alcohol. They retain a red color. If mycolic acid layer is removed, they will stain gram-positive.
Archaea Cell Wall: They can lack walls or have walls composed of polysaccharides and proteins that are not peptidoglycan but are similar, pseudomurein. Pseudomurein contains N-acetyltalosaminuronic acid instead of NAM and lacks D-amino acids. Cannot be Gram-stained positive because they lack peptidoglycan.
Mycoplasmas Cell Wall: They are bacteria without a cell wall. They are the smallest and pass through most bacterial filters. Their plasma membrane is unique as it has lipids called sterols, which help protect them from lysis.
Differentiate protoplast, spheroplast, and L form.
Protoplast: Protoplasts occur when the cellular contents remain surrounded by the plasma membrane of gram-positive bacteria do not undergo lysis. Cell walls of gram-positive bacteria can be damaged by exposure to lysozyme. It catalyzes hydrolysis of the bonds between sugars in the repeating disaccharide backbone of peptidoglycan.
Spheroplast: Spheroplasts occur when gram-negative cells first interact with EDTA, weakening the ionic bonds in the outer membrane and damaging it, and then using lysozyme to access the peptidoglycan layer. The wall is not destroyed like gram-positive cells and some of the outer membrane remains.
L form: Cells of the genus Proteus (as well as other genera) that lose their cell walls and swell into irregular shaped cells. May spontaneously form or develop in response to penicillin or lysozyme. Can live and divide repeatedly or even return to the walled state.
Protoplasts, spheroplasts, and L forms will burst in pure water or very dilute salt or sugar solutions, undergoing osmotic lysis.
4.5 Structures Internal to the Cell Wall
Describe the structure, chemistry, and functions of the prokaryotic plasma membrane.
The plasma membrane consists primarily of phospholipids and proteins. They are less rigid due to the lack of sterols, the membrane is less rigid (with exception to Mycoplasma which does have membrane sterols). The bacterial plasma membrane is a phospholipid bilayer, with a polar, hydrophilic head composed of a phosphate group and glycerol and a nonpolar, hydrophobic tail composed of fatty acids.
Proteins in the membrane are arranged as peripheral or integral proteins:
Peripheral Proteins:
Located at the inner or outer surface of the membrane.
Easily removed by mild treatments.
Functions:
Catalyze chemical reactions (enzymes).
Provide structural support (scaffold).
Mediate changes in membrane shape during movement.
Integral Proteins:
Removed only by disrupting the lipid bilayer (using detergents).
Most penetrate the membrane as transmembrane proteins.
Some serve as channels for substance transport.
Glycoproteins and Glycolipids:
Proteins/lipids with carbohydrates attached.
Functions:
Protect and lubricate the cell.
Involved in cell-to-cell interactions.
Example: Some viruses (e.g., influenza) enter cells by binding to glycoproteins.
Fluid Mosaic Model:
The phospholipid and protein molecules move freely within the membrane.
Phospholipids form a self-sealing bilayer in water due to fatty acid tails.
Membrane viscosity is comparable to olive oil, allowing protein movement without damaging the membrane structure.
The plasma membrane’s primary function is selective permeability, which depends on several factors. Larger molecules (proteins) cannot fit through phospholipid bilayer, but smaller molecules like water, oxygen, carbon dioxide, and simple sugars pass easily. Ions penetrate slowly. Nonpolar molecules usually pass through easily. The plasma membrane also contains enzymes to catalyze the breakdown of nutrients and produce ATP. For some bacteria, pigments and enzymes involved with photosynthesis are found in infoldings of plasma membrane that extend into the cytoplasm, called chromatophores. However, the photosynthetic thylakoid membranes of cyanobacteria may be separate from plasma membrane, resembling chloroplasts. Electron microscopes have shown irregular folds called mesosomes, which are speculated to form when the membrane is damaged.
Define simple diffusion, facilitated diffusion, osmosis, active transport, and group translocation.
Simple diffusion: the net overall movement of molecules or ions from an area of high concentration to an area of low concentration, until equilibrium is reached.
Facilitated diffusion: Transporter proteins or permeases in the membrane serve as channels for ions or large molecules without expending energy. These transporters are usually nonspecific and allow a wide variety of ins or molecules. If molecules are too large, the bacteria will release extracellular enzymes to catalyze them into simpler molecules.
Osmosis: This is the process of water moving through the membrane either through simple diffusion or through aquaporins (integral membrane proteins). Through osmosis and osmotic pressure, the bacterial cell can be isotonic (equal pressure), hypotonic (where water is forced into the cell due to higher solute concentration; gram-negative bacteria may burst of undergo osmotic lysis), or hypertonic (the cell has lower concentration of solutes; most bacteria will shrink and collapse, called plasmolyze.)
Active Transport: The cell uses ATP to move substances across plasma membrane like ions (NA⁺, K⁺, H⁺, Ca²⁺, and Cl⁻), amino acids, and simple sugars. While passive processes work, it can help move materials against the concentration gradient. Different transporter for each substance or group of related substances.
Group translocation: Exclusive to prokaryotes where the substance is chemically altered during transport process. Once inside membrane, it is impermeable to it. This helps cells acquire resources even in low concentrations. Requires energy supplied by high-energy phosphate compounds, such as phosphoenolpyruvic acid (PEP). With glucose, a phosphate group is added to the sugar. This phosphorylated form of glucose, which cannot be transported out, can then be used in the cell’s metabolic pathways.
Identify the functions of the nucleoid and ribosomes.
Nucleoid and Plasmids in Bacterial Cells
The nucleoid typically contains a single, long, double-stranded DNA thread called the bacterial chromosome.
This chromosome carries the genetic information necessary for the cell's structures and functions.
Unlike eukaryotic chromosomes, bacterial chromosomes do not have a nuclear envelope and lack histones.
The nucleoid shape can be spherical, elongated, or dumbbell-shaped.
In actively growing bacteria, DNA can occupy about 20% of the cell volume, as it pre-synthesizes for future cells.
The bacterial chromosome is attached to the plasma membrane, which aids in the replication and segregation of chromosomes during cell division.
Bacteria may also contain plasmids, which are small, circular, double-stranded DNA molecules that replicate independently of the bacterial chromosome.
Plasmids are extrachromosomal genetic elements and usually contain 5 to 100 genes that are not essential for survival under normal conditions.
Plasmids can provide advantages, such as antibiotic resistance, tolerance to toxic metals, toxin production, and enzyme synthesis.
Plasmids can be transferred between bacteria and are utilized in biotechnology for gene manipulation.
Ribosomes: All eukaryotic and prokaryotic cells contain ribosomes where protein synthesis occurs. Cells with high rates of protein synthesis have more ribosomes. Prokaryotic cell cytoplasm contains many ribosomes, giving it a granular look. Ribosomes consist of two subunits made of proteins and ribosomal RNA (rRNA). Prokaryotic ribosomes (70S) are smaller and different in composition from eukaryotic ribosomes (80S). The 70S ribosome is made of a 30S subunit (containing 1 rRNA) and a 50S subunit (containing 2 rRNA). The "S" stands for Svedberg units, indicating sedimentation rate based on size, weight, and shape, not a direct sum of the subunits.
Identify the functions of four inclusions.
Inclusions in prokaryotic cells serve as storage or reserve materials and can include:
Metachromatic granules: Also known as volutin, store inorganic phosphate, which can be used in nucleic acid synthesis and ATP production. Stain red with certain blue dyes. grows in phosphate-rich environments. Are a characteristic of Corynebacterium diphtheriae.
Polysaccharide granules: Serve as energy reserves, typically composed of glycogen or starch. Presence is known when in contact with iodine since glycogen appear reddish brown and starch appear blue.
Lipid inclusions: Store lipids as energy reserves, which can be used for cell metabolism. Appear in species of Mycobacterium, Bacillus, Azotobacter, Spirillum, and other genera. Revealed by staining cells with fat-soluble dyes.
Sulfur granules: Serve as energy reserves for certain bacteria that can utilize sulfur for metabolic processes.
Describe the functions of endospores, sporulation, and endospore germination.
Endospores: Specialized resting cells the form from gram-positive bacteria when essential nutrients are depleted. They are highly durable dehydrated cells with the thick walls and additional layers. Can survive extreme heat, lack of water, and exposure to toxic chemicals and radiation. Coxiella burnetii, a gram-negative bacteria can form endospores that cause Q fever. Boiling is not effective.
Sporulation: the several-hour long process for endospores to form within a vegetative cell. Usually form when key nutrient like carbon or nitrogen is scarce. During sporulation, the first observable stage involves the formation of a forespore, created by an ingrowth of the plasma membrane (spore septum) that isolates the replicated bacterial chromosome and a small portion of cytoplasm. This forespore is surrounded by a double-layered membrane. Between these membranes, thick layers of peptidoglycan are deposited, followed by the formation of a protein-rich spore coat that provides resistance to harsh chemicals. Eventually, the original cell degrades, leading to the release of the endospore.
Endospore germination: a means of restarting the bacteria by being triggered from high heat or small triggering molecules, germinants, alanine and inosine.
4.6 Flagella and Cilia
Differentiate prokaryotic and eukaryotic flagella.
Eukaryotic cells have flagella (long in size and few) and cilia (numerous and short) Algae, like Euglena, use flagellum for locomotion while protozoa, like Tetrahymena, use cilia for locomotion. Both consist of nine pairs of microtubules (doublets) arranged in a ring, plus another two microtubules in the center of the ring, an arrangement called a 9 + 2 array. Microtubules are long, hollow tubes made of protein called tubulin.
A prokaryotic flagellum rotates, but eukaryotic flagella move like a wave.
4.7
Compare and contrast prokaryotic and eukaryotic cell walls and glycocalyxes.
Many eukaryotes have simpler cell walls. many algae have cell walls made of cellulose. Fungi have cellulose but most of cell wall is based upon chitin, a polymer of NAG units. Cell walls of yeast contain glucan and mannan. Eukaryotes without a cell wall have a thin membrane but those in contact with the environment may have coatings. Protozoa have an atypical flexible outer protein called a pellicle.
Other eukaryotic cells (animals included) have membrane covered by a glycocalyx, a layer of substantial amounts of sticky carbs. Some carbs are covalently bound to proteins, glycoproteins, and lipids, glycolipids. It helps strengthen cell surface, help attach cells, and enable cell recognition.
4.8 - 4.10
Compare and contrast prokaryotic and eukaryotic plasma membranes.
Eukaryote and prokaryote plasma membranes have different proteins.
Eukaryotic plasma membrane:
Contain carbs which serve as attachment sites for bacteria and receptor sites for cell-to-cell recognition.
Contain sterols to help membranes resist lysis
Eukaryotic cells can perform endocytosis, where material is brought into the cell by having the membrane wrap around it. Three types:
phagocytosis: Cellular projections engulf particles and bring into cell; used by white blood cells.
Pinocytosis: membrane folds inward, bringing extracellular fluid and substances in.
Receptor-mediated endocytosis: substances bind to the receptors and cause the membrane to fold in. It’s a way viruses can enter.
The cytoplasm of eukaryotic cells is the substance found between the plasma membrane and the nucleus, containing various cellular components. The fluid portion of the cytoplasm is referred to as cytosol, while the cytoskeleton consists of microfilaments, intermediate filaments, and microtubules, corresponding to components found in prokaryotes. The eukaryotic cytoskeleton provides structural support, shape, and aids in transporting substances, including movement during phagocytosis. Cytoplasmic streaming refers to the movement of cytoplasm within the cell, facilitating nutrient distribution, whereas important enzymes in prokaryotic cytoplasm are compartmentalized in eukaryotic organelles.
Eukaryotic ribosomes are larger than prokaryotic ribosomes. These eukaryotic ribosomes are S ribosomes, each of which consists of a large S sub unit containing three molecules of rRNA and a smaller S subunit with one molecule of rRNA. They are made in the nucleus. However, prokaryotic ribosomes are made in the cytoplasm.
4.11: Organelles
Define organelle.
A membrane0enclosed structure within eukaryotic cells each with specific functions.
Describe the functions of the nucleus, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes, and centrosomes.
Functions of Organelles in Eukaryotic Cells:
Nucleus: Nucleus has a double membrane, nuclear envelope, that contains nuclear pores to communicate with the cytoplasm. Nucleoli are spherical bodies in nuclear envelope that are condensed regions of chromosomes where ribosomal RNA is synthesized. The nucleus houses most of the cell's DNA, which combines with proteins, including histones and nonhistones, to form nucleosomes. When the cell is not reproducing, this DNA-protein complex appears as chromatin, a threadlike mass. During nuclear division, chromatin condenses into shorter, thicker structures known as chromosomes. Mitosis and Meiosis needed to segregate chromosomes.
Endoplasmic Reticulum: Continuous with the nuclear envelope. Two different forms of ER:
Rough ER: Outer surface studded with ribosomes for protein synthesis. Synthesized proteins enter cisterns in ER for processing and sorting. Sometimes, enzymes attach proteins to carbs to form glycoproteins, and other times attach proteins to phospholipids. Rough ER synthesizes secretory proteins and membrane molecules
Smooth ER: Extends from rough ER to form network of membrane tubules. No ribosomes, but contains enzymes to become more diverse than rough ER. Like ER, it synthesizes phospholipids. Also synthesizes fats and steroids. In liver cells, it helps release glucose in bloodstream and inactivate/detoxify drugs and other harmful substances. Releases calcium ions in muscle cells to trigger contraction process.
Golgi Complex: It’s like the mail service. Proteins synthesized by ribosomes are encased in ER membrane, called a transport vesicle. It fuses with the Golgi complex, releasing into the cisterns. Proteins modified in one cistern and transported to another via transfer vesicles. Enzymes in cisterns form proteins to become glycoproteins, glycolipids, and lipoproteins. Some of processed proteins leave in secretory vesicles to go to plasma membrane to be discharged via exocytosis. Some are transported to become a part of plasma membrane. Finally, some leave in vesicles called storage vesicles.
Lysosomes: Major storage vesicle only in animal cells. Formed from Golgi complexes and only have a single membrane with no internal structure. But, they contain 40 different digestive enzymes to break down various molecules.
Vacuoles: A space or cavity in cell that is enclosed by a membrane called a tonoplast. Plants have much larger vacuoles that take up 5-90% of cell volume. Some serve as temporary storage organelles; others form during endocytosis to bring food in cell. Also store metabolic wastes and poisons. May also take up excessive water.
Mitochondria: POWERHOUSE OF THE CELL. Two membranes. external membrane is smooth but the internal is arranged in a series of folds, mitochondrial cristae. Center of mitochondrion is semifluid substance called mitochondrial matrix. ATP production. Have 70S ribosomes and some DNA of their own.
Chloroplasts: Main source for photosynthesis and has 70S ribosomes. Double membrane-enclosed and contains both the pigment chlorophyll and enzymes for photosynthesis. Chlorophyll contained in flat membranes called thylakoids and thylakoids stacked as grana. Internal fluid of chloroplast is the stroma.
Peroxisomes: Similar to lysosomes but smaller and contain one or more enzymes to break down various organic substances. Most likely for from budding off ER. By-product of molecular breakdown is hydrogen peroxide, which the peroxisomes have catalase to break down hydrogen peroxide.
Centrosomes: Organizes the mitotic spindle for cell division. Near the nucleus in animal cells and has two components:
Pericentriolar matrix: Region of cytosol with dense network of small protein fibers.
Centrioles: Pair of cylindrical structures within pericentriolar matrix. Nine clusters of 3 microtubules in circular pattern and arranged in 9 + 0 array (9 microtubules around and 0 center microtubules). Long axis of one centriole at right angle to other.
4.12 Evolution of Eukaryotic Cells
Discuss evidence that supports the endosymbiotic theory of eukaryotic evolution
Both mitochondria and chloroplasts resemble bacteria in size and shape as well as contain circular DNA. Mitochondrial and chloroplast ribosomes resemble prokaryotes. Same antibiotics that inhibit protein synthesis bacteria inhibit it for mitochondria and chloroplasts.
