Prokaryotic & Eukaryotic Cell Profiles and Microbial Metabolism
Chapter 4 – Prokaryotic & Eukaryotic Cell Profiles
Monomorphic and Pleomorphic
Monomorphic: A term used to describe organisms that have a consistent shape.
Pleomorphic: Refers to organisms that can have multiple shapes due to variations in their environmental conditions or genetic makeup.
Basic Shapes of Bacteria
Coccus: Spherical or round-shaped bacteria.
Bacillus: Rod-shaped bacteria.
Vibrio: Comma-shaped bacteria.
Coccobacillus: Short and plump rod-shaped bacteria, an intermediate between cocci and bacilli.
Spirilla: Corkscrew-shaped bacteria.
Spirochete: Long, thin, spiral-shaped bacteria that are flexible.
Less Common Bacterial Shapes: Includes shapes such as square, star-shaped, and filamentous.
Bacterial Cell Arrangements
Diplo: Pairs of bacteria (e.g., diplococci).
Strepto: Chains of bacteria (e.g., streptobacilli).
Staphylo: Clusters of bacteria (e.g., staphylococci).
Tetrads: Groups of four cocci.
Sarcinae: Cubic arrangements of cocci (8 or more).
Bacterial Cell Description: The combination of cell shape and arrangement leads to descriptions (e.g., streptobacilli indicates a rod shape arranged in a chain).
Fluid Mosaic Model of the Cell Membrane:
A model describing the structure of the cell membrane as a mosaic of various proteins embedded in a fluid lipid bilayer, allowing for dynamic movement and flexibility.
Structure, Chemistry, and Functions of the Prokaryotic Cell Membrane
Composed mainly of phospholipids and proteins; it regulates what enters and exits the cell, provides structural support, and facilitates communication with the environment.
Functions of the Plasma Membrane:
Selective permeable barrier, transport of substances, energy generation, signaling, and structural support.
Peripheral Proteins:
Proteins located on the surface of the membrane.
Functions include signaling, maintaining cell structure, and playing a role in transport without spanning the membrane.
Integral Proteins:
Proteins that are embedded within the membrane.
Functions include transport of molecules across the membrane and acting as receptors for signaling.
Definitions:
Simple Diffusion: The process where particles move from an area of higher concentration to an area of lower concentration without the need for energy.
Facilitated Diffusion: Movement of substances across the membrane via specific transport proteins, down their concentration gradient, without energy expenditure.
Osmosis: The movement of water across a semipermeable membrane from a region of low solute concentration to a region of high solute concentration.
Active Transport: The process of moving molecules against their concentration gradient, requiring energy (ATP).
Group Translocation: A form of active transport where a substance is chemically modified during transport across the membrane, ensuring it remains inside the cell.
Cell Walls:
Rigid structures outside the cell membrane in prokaryotes that provide shape, protection, and support.
Functions of the Cell Wall: Protects the cell from osmotic pressure differences, maintains cell shape, and facilitates cell differentiation.
Composition: Mainly composed of peptidoglycan in bacteria; includes glycan chains (N-acetylglucosamine and N-acetylmuramic acid) and peptide cross-links.
Gram-positive Cell Wall:
Thick peptidoglycan layer with polypeptide chains; retains the crystal violet stain during Gram staining.
Lipoteichoic Acid and Wall Teichoic Acid: Polymers that extend through the peptidoglycan layer; involved in maintaining cell shape and regulating ion movement.
Gram-negative Cell Wall:
Thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharides (LPS).
Periplasm: The space between the inner and outer membranes in Gram-negative bacteria containing various enzymes and transport proteins.
Benefits of the Outer Membrane in Gram-negative Bacteria: Provides an additional barrier, protecting against certain chemicals, and serves as a site for some metabolic processes.
Porins: Proteins that form channels in the outer membrane, allowing specific molecules to pass through.
Components of the Outer Membrane:
Lipopolysaccharides (LPS), phospholipids, porins, and proteins.
Lipopolysaccharide (LPS): Composed of three components:
Lipid A: Anchors LPS in the membrane, can be toxic.
Core Polysaccharide: Attached to Lipid A and important for structural stability.
O Polysaccharide: Extends out and can act as an antigen; varies among bacterial species.
Atypical Cell Walls:
Examples include mycoplasmas with no cell wall or organisms with waxy cell walls, such as mycobacteria.
Cell Wall Damage: Various agents (like antibiotics) can disrupt the synthesis of peptidoglycan, leading to cell lysis.
External Structures of Prokaryotic Cells: Include the glycocalyx, flagella, fimbriae, and pili.
Glycocalyx: A sticky layer of polysaccharides found outside the cell wall, aiding in attachment and protection.
Capsule and Slime Layer:
Capsule: A well-defined, organized layer that functions in protection against phagocytosis.
Slime Layer: A looser, less organized structure providing similar functions.
Functions of the Glycocalyx:
Protection from desiccation, nutrient retention, evasion of host immune response, and biofilm formation.
Definitions:
Phagocytosis: The process by which certain cells engulf and digest foreign particles or pathogens.
Biofilm: A structured community of bacteria encapsulated within a self-produced matrix adhering to surfaces.
Flagella: Tail-like structures that aid in bacterial motility.
Flagella Patterns:
Atrichous: No flagella.
Peritrichous: Flagella dispersed over the entire surface.
Monotrichous: A single flagellum located at one pole.
Lophotrichous: A tuft of flagella at one or both ends.
Amphitrichous: One flagellum at each end.
Parts of a Flagellum: Includes the filament, hook, and basal body.
Differences in Flagella of Gram-positive and Gram-negative Cells: Gram-negative cells have a more complex structure, with an additional outer membrane and a basal body that anchors to both membranes.
Motility and Movement Using Flagella: Bacteria can move via undulating motion of the flagella.
Run/Swim: Smooth, straight movement.
Tumble: A change in direction; allows bacteria to navigate towards stimuli.
Axial Filaments: Flagella that are found within the periplasmic space of spirochetes, providing motility through a corkscrew motion.
Fimbriae: Short, hair-like structures used for attachment and biofilm formation.
Pili (Pilus): Longer than fimbriae; involved in conjugation (DNA transfer) and attachment.
Internal Prokaryotic Structures: Include structures such as the cytoplasm, nucleoid, ribosomes, and inclusions.
Cytoplasm: Gel-like substance within the cell membrane, containing water, proteins, and other macromolecules necessary for cellular functions.
Nucleoid: A region where the bacterial chromosome is located; it’s not enclosed in a membrane.
Bacterial Chromosome: A single, circular DNA molecule that differs from eukaryotic chromosomes, which are typically linear and associated with histone proteins.
Storage of Prokaryotic vs Eukaryotic DNA: Prokaryotic DNA is generally compact and does not have introns; eukaryotic DNA contains numerous regulatory sequences and introns.
Plasmid: Small circular DNA molecules independent of chromosomal DNA, often carrying genes for antibiotic resistance or other functions.
Advantages of Plasmids: Allow for genetic variation and adaptability; can replicate independently from chromosomal DNA.
Ribosomes:
Sites of protein synthesis, found free within the cytoplasm or attached to the cell membrane.
Difference Between Prokaryotic and Eukaryotic Ribosomes: Prokaryotic ribosomes (70S) are smaller than eukaryotic ribosomes (80S).
Prokaryotic Ribosome Subunits: 30S and 50S.
Complete Ribosome: Known as 70S ribosome in prokaryotes when combining both subunits.
Inclusions: Storage granules within the cytoplasm used to hold important substances (e.g., glycogen, lipids).
Examples of Inclusions: Poly-β-hydroxybutyrate granules (energy reserves) and gas vesicles (buoyancy in aquatic environments).
Endospore: A resistant structure formed by some bacteria (e.g., Bacillus and Clostridium) that enables survival in harsh conditions.
Sporulation: The process by which endospores are formed, usually triggered by nutrient deprivation.
Stages of Sporulation: Involves DNA replication, asymmetric cell division, and encasement of the DNA into a tough spore coat.
Germination: The process by which an endospore resumes growth when conditions improve.
Eukaryotes: Include organisms such as plants, animals, fungi, and protists.
Eukaryotic Plasma Membrane: Similar fluid mosaic model as prokaryotes but often contains sterols for added stability.
Eukaryotic Cell Walls:
Composed of cellulose in plants, chitin in fungi, and silica in some algae.
Eukaryotic Glycocalyx: Similar to prokaryotic glycocalyx, playing roles in protection, communication, and adhesion.
Locomotion in Eukaryotes: Often through cilia, flagella, or amoeboid movement.
Differences in Ribosomes: Eukaryotic ribosomes (80S) differ from prokaryotic ribosomes (70S) in composition and size.
Organelles: Specialized structures within eukaryotic cells, each performing a unique function (e.g., respiration, photosynthesis).
Structure and Function of Eukaryotic Organelles:[
Mitochondria: Powerhouse of the cell, site of ATP production through aerobic respiration.
Rough Endoplasmic Reticulum: Studded with ribosomes, synthesizes and processes proteins.
Smooth Endoplasmic Reticulum: Lacks ribosomes, synthesizes lipids, detoxifies drugs, and stores calcium.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.
Centrioles: Involved in cell division and formation of cilia and flagella.
Peroxisomes: Contain enzymes for oxidation reactions, breaking down fatty acids and detoxifying harmful substances.
Endosymbiotic Theory: Explains the origin of mitochondria and chloroplasts as formerly free-living prokaryotes that were engulfed by ancestral eukaryotic cells, leading to a symbiotic relationship.
Purpose of the Eukaryotic Cytoskeleton: Provides structural support, facilitates intracellular transport, and organizes the cell's contents and helps in cell division.
Structure and Function of Cytoskeletal Elements:
Microfilaments: Composed of actin, involved in muscle contraction and cell movement.
Intermediate Filaments: Provide mechanical support and stabilize cell structure.
Microtubules: Composed of tubulin, important for maintaining cell shape, motility, and cell division.
Chapter 5 – Microbial Metabolism
Metabolism: The sum of all chemical reactions occurring within a cell; it encompasses all processes for energy production and biosynthesis of cellular components.
Two Classes of Metabolic Reactions:
Catabolism: Breakdown of complex molecules into simpler ones, often releasing energy (e.g., cellular respiration).
Anabolism: Synthesis of complex molecules from simpler ones, consuming energy (e.g., protein synthesis).
Coupling of Reactions: Anabolic and catabolic processes are linked through ATP, which stores energy produced from catabolic pathways to fuel anabolic reactions.
Metabolic Pathways: A series of chemical reactions catalyzed by enzymes to convert a substrate into a specific product, often divided into linear or cyclical pathways.
Catalyst: A substance that accelerates a chemical reaction without being consumed in the process.
Enzyme: Biological catalysts, typically proteins, that facilitate chemical reactions by lowering the activation energy required for the reaction to proceed.
Enzyme Nomenclature: Named based on the substrate or type of reaction, often with the suffix “-ase” (e.g., lactase for lactose).
Activation Energy: The minimum energy required to initiate a chemical reaction; enzymes lower this barrier, increasing reaction rates.
Reactants of Chemical Reactions: Substances consumed in a reaction to form products.
Products of Chemical Reactions: Substances produced as a result of a chemical reaction.
Substrates: The specific reactants that an enzyme acts upon during a reaction.
Active Site of an Enzyme: The region on the enzyme where the substrate binds, resulting in the formation of an enzyme-substrate complex.
Enzyme-Substrate Complex: The transient complex formed when an enzyme binds to its substrate, leading to a catalytic reaction.
Induced Fit: A model describing how the enzyme changes shape to better fit the substrate upon binding, optimizing the reaction.
Factors Influencing Enzyme Activity:
Temperature: Increasing temperature can enhance activity up to an optimal point, beyond which enzymes may denature.
pH: Each enzyme has an optimal pH range; extreme deviations can lead to denaturation.
Substrate Concentration: Increased substrate concentration enhances activity until saturation is reached.
Apoenzyme: The protein portion of an enzyme, inactive until combined with a cofactor.
Cofactor: A non-protein component that assists in enzyme activity, which can be a metal ion (e.g., Mg²⁺) or an organic molecule (coenzyme).
Coenzyme: An organic cofactor that often serves as a carrier for molecules during reactions (e.g., NAD⁺, FAD).
Holoenzyme: The complete, active form of an enzyme, consisting of the apoenzyme and its necessary cofactors.
Electron Carriers: Molecules that transport electrons (or hydrogen atoms) during metabolic reactions.
Main Electron Carriers:
NAD (Nicotinamide adenine dinucleotide): Involved in redox reactions, existing in oxidized (NAD⁺) and reduced (NADH) forms.
NADP (Nicotinamide adenine dinucleotide phosphate): Similar to NAD, serving mainly in anabolic reactions; oxidized (NADP⁺) and reduced (NADPH) forms.
FAD (Flavin adenine dinucleotide): Another redox carrier, in oxidized (FAD) and reduced (FADH₂) forms.
Oxidation of a Molecule: The process in which a molecule loses electrons (or hydrogen) during a reaction, often releasing energy.
Reduction of a Molecule: The gain of electrons (or hydrogen) by a molecule, requiring energy input.
Oxidation-Reduction (Redox) Reactions: Reactions that involve the transfer of electrons between substances, where one is oxidized and the other is reduced.
Oxidized and Reduced Forms of Electron Carriers:
NAD⁺ (oxidized) ↔ NADH (reduced)
NADP⁺ (oxidized) ↔ NADPH (reduced)
FAD (oxidized) ↔ FADH₂ (reduced)
Trapping Energy in Redox Reactions: Energy released from oxidation can be conserved in the form of ATP through substrate-level phosphorylation and oxidative phosphorylation.
ATP Generation:
ATP is produced in various processes: substrate-level phosphorylation, oxidative phosphorylation during electron transport, and photophosphorylation in photosynthetic organisms.
Primary Source of Cellular Energy: ATP serves as the main energy currency used by microorganisms for cellular work.
Carbohydrate Catabolism: The breakdown of carbohydrates (primarily glucose) to produce energy.
Processes Utilized:
Glycolysis: Breakdown of glucose to pyruvic acid, yielding ATP and NADH.
Krebs Cycle: Completes the oxidation of glucose products, yielding additional ATP, NADH, and FADH₂.
Stages of Cellular Metabolism:
Glycolysis
Krebs Cycle
Electron Transport Chain
Glycolysis: An anaerobic process that converts glucose into two molecules of pyruvic acid, producing a net gain of 2 ATP and 2 NADH.
Initial and Final Substances: Starts with glucose and results in pyruvic acid.
Key Features of Glycolysis: Involves 10 enzymatic steps, occurs in the cytoplasm, and can proceed under aerobic or anaerobic conditions.
Substrate-Level Phosphorylation: Direct transfer of a phosphate group from a substrate to ADP to form ATP during glycolysis and Krebs cycle.
Krebs Cycle (TCA Cycle, Citric Acid Cycle): Aerobic process occurring in mitochondrial matrix (in eukaryotes) and cytoplasm (in prokaryotes), processing acetyl-CoA into carbon dioxide and transferring high-energy electrons to NAD⁺ and FAD.
Net Outputs per Turn of the Krebs Cycle:
3 NADH
1 FADH₂
1 ATP
2 CO₂
Comparison: Enzymatic paths in glycolysis and Krebs cycle yield differing products, critical for metabolic processing set in interlinked metabolic pathways.
Chemical Reactions of Glycolysis: Key actions in breaking down glucose and transferring energy to ATP and electron carriers.
Pentose Phosphate and Entner-Doudoroff Pathways: Alternative routes for carbohydrate metabolism yielding NADPH and other metabolites, playing roles in anabolic reactions.
Chemiosmotic Model for ATP Generation: Proposes that a proton gradient across the inner mitochondrial membrane is created during electron transport, driving ATP synthesis when protons flow back through ATP synthase.
Aerobic vs Anaerobic Respiration:
Aerobic respiration: Uses oxygen as the final electron acceptor in the electron transport chain, resulting in higher ATP yield.
Anaerobic respiration: Utilizes other molecules (e.g., nitrate, sulfate) in the absence of oxygen, resulting in less ATP production.
Fermentation: Ananaerobic process that converts glucose into acids or alcohols, producing ATP via substrate-level phosphorylation.
Overall Function of Metabolic Pathways: To produce energy efficiently, synthesize cellular materials, and respond to environmental changes.
ATP as an Intermediate: Links catabolism and anabolism; energy from catabolic processes is stored in ATP and used for anabolic processes.
Enzyme Specificity: Ensures that enzymes catalyze specific reactions efficiently; improper binding could lead to futile pathways.
Temperature and Enzyme Activity:
Below optimal temperature: Enzyme activity decreases, slowing reaction rates.
Above optimal temperature: Enzyme denaturation occurs, leading to loss of function.
Feedback Inhibition: A form of non-competitive inhibition where the end product of a pathway inhibits an earlier enzyme to regulate metabolic flow.
Electron Transport Chain Carrier Molecules: Function by transferring high-energy electrons from NADH and FADH₂ through a series of proteins, ultimately generating ATP via oxidative phosphorylation.
Energy Yield Comparison: Aerobic respiration yields approximately 29-38 ATP molecules per glucose, while anaerobic respiration yields 2-36 ATP depending on the electron acceptor used.
Chapter 6 – Microbial Growth
Microbial Growth: Generally refers to an increase in cell number rather than increase in cell size.
Colonies: Visible clusters of microorganisms derived from a single progenitor cell, indicative of microbial growth under suitable conditions.
Reproduction in Bacteria: Primarily asexual, predominantly through binary fission rather than sexual reproduction.
Budding: A form of asexual reproduction whereby a new organism develops from an outgrowth of the parent.
Binary Fission: A method where a single bacterial cell divides into two identical daughter cells.
Cell Division Increase: With each cycle of division, the bacterial population doubles.
Generation Number: Refers to the number of bacterial cells resulting from a specific number of divisions; calculated as N = N_0 imes 2^n where N is the final count, N_0 is the initial count, and n is the number of generations.
Generation Time: The time it takes for a bacterial population to double in number, varies based on species and environmental factors.
Microbial Growth Curve: A graph plotting the growth of a microbial culture over time, typically divided into four phases:
Lag Phase: Adaptation to the environment; minimal cell division.
Log Phase: Exponential growth occurs; cells divide rapidly.
Stationary Phase: Growth rate slows; nutrient depletion and waste accumulation stabilize cell numbers.
Death Phase: Cells begin to die off due to environmental stressors and resource depletion.
Chemical Components Required for Microbial Life: Essential elements (carbon, nitrogen, oxygen, sulfur, phosphorus) and macromolecules (proteins, nucleic acids, lipids, carbohydrates).
Aerobes and Anaerobes:
Aerobe: Requires oxygen for growth.
Anaerobe: Grows in the absence of oxygen, can be classified as:
Obligate Aerobe: Must have oxygen.
Facultative Anaerobe: Can grow with or without oxygen.
Obligate Anaerobe: Cannot tolerate oxygen.
Aerotolerant Anaerobe: Can tolerate oxygen but does not use it.
Microaerophile: Requires lower than atmospheric oxygen levels.
Physical Requirements for Growth:
Temperature: Optimal temperature ranges define microbial growth.
pH: Most bacteria grow best between pH 6.5 and 7.5 but can vary by species.
Osmotic Pressure: Refers to the use of salts and sugars to preserve food; osmotic pressure influences cell structure and growth rates.
Microbial Temperature Groups:
Psychrophiles: Grow optimally at low temperatures (0-15°C).
Psychrotrophs: Grow between 20-30°C, can spoil refrigerated foods.
Mesophiles: Optimal growth at moderate temperatures (20-45°C), most human pathogens fall in this group.
Thermophiles: Prefer high temperatures (45-80°C), found in hot springs.
Hyperthermophiles: Thrive at extremely high temperatures (>80°C).
pH Classifications:
Acidophiles: Prefer acidic environments (pH < 6).
Neutrophiles: Grow best at neutral pH (6.5-7.5).
Alkaliphiles: Prefer alkaline environments (pH > 8).
Halophiles Classification:
Extreme Halophiles: Requires high salt concentrations for growth.
Facultative Halophiles: Can tolerate high salt concentrations but do not require them.
Osmotic Pressure and Growth: Influences water activity in cells; hypertonic environments can lead to plasmolysis, inhibiting growth.
Classification by Oxygen Requirements: Organisms can be divided based on their need or tolerance of oxygen in their growth requirements.
Biofilm Formation: Microbial colonies encased in a matrix, leading to increased resistance to antibiotics and host immune responses, complicating infections.
Chemically Defined vs Complex Media:
Chemically Defined Media: Composition is known precisely, consisting of pure biochemicals.
Complex Media: Contains extracts such as yeast or beef, whose exact chemical composition is not known but supports growth of a wide array of organisms.
Isolation of Pure Cultures: Techniques like the streak plate method allow for the separation of individual microbial colonies from a mixed culture.
Phases of Microbial Growth: A comparison of generation times and growth phases.
Direct Methods of Measuring Cell Growth: Involves counting live cells directly (e.g., using a hemocytometer).
Indirect Methods: Measures cell growth indirectly through turbidity, metabolic activity, and dry weight analysis.