Cell Structure and Function Overview

Prokaryotic Cells

  • Unicellular organisms that lack a nucleus and membrane-bound organelles. They are generally smaller than eukaryotic cells, with a diameter of about 0.1 to 5.0 micrometers.

  • Prokaryotes include Bacteria and Archaea, which have distinct biochemical and genetic characteristics.

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Eukaryotic Cells

  • Cells that contain membrane-bound organelles, including a true nucleus, allowing for compartmentalization of cellular functions.

  • Eukaryotic organisms can be unicellular (e.g., yeast) or multicellular (e.g., plants, animals, and fungi).

Nucleus

  • Stores genetic material (DNA) and serves as the control center of the cell, regulating gene expression and mediating cellular activities such as metabolism, growth, and reproduction.

  • Surrounded by a double membrane known as the nuclear envelope which contains pores for transport of molecules.

Nucleolus

  • Produces ribosomal RNA (rRNA) and assembles ribosomes, which are essential for protein synthesis.

  • It is a dense structure within the nucleus, often spherical, reflecting the cell's protein synthesis demands.

Ribosomes

  • Synthesizes proteins by translating messenger RNA (mRNA) sequences. Ribosomes can be found freely in the cytoplasm or attached to the rough endoplasmic reticulum (ER).

  • Composed of two subunits (large and small), which come together during translation.

Rough ER

  • Involved in protein folding, modification, and transport. It has a studded appearance due to ribosomes on its surface.

  • Functions in the synthesis of glycoproteins and membrane proteins as well as the initial stages of protein processing.

Smooth ER

  • Synthesizes lipids, detoxifies drugs, and stores calcium ions. It lacks ribosomes, giving it a smooth appearance.

  • Plays a crucial role in carbohydrate metabolism and synthesis of steroid hormones.

Golgi Apparatus

  • Modifies, sorts, and packages proteins and lipids for transport, both inside and outside of the cell.

  • Consists of stacked membrane-bound sacs called cisternae, where further modifications such as glycosylation may occur.

Mitochondria

  • Generates ATP (adenosine triphosphate) through aerobic respiration, the main energy currency of the cell. They have a double membrane structure, with an inner membrane folded into cristae, increasing surface area for energy production.

  • Contains its own DNA, which is circular and similar to bacterial DNA, suggesting an endosymbiotic origin.

Chloroplasts

  • Conducts photosynthesis in plant cells and some algae, converting light energy into chemical energy. They contain chlorophyll, a pigment crucial for capturing light energy.

  • Also have a double membrane and their own DNA, indicative of their evolutionary history as free-living prokaryotes.

Lysosomes

  • Contains hydrolytic enzymes for digestion of waste materials, pathogens, and old organelles, acting as the cell's recycling center.

  • They maintain an acidic environment for optimal enzyme activity and can also initiate autophagy for cellular maintenance.

Peroxisomes

  • Breaks down fatty acids and neutralizes toxic compounds such as hydrogen peroxide via oxidative reactions.

  • Contain enzymes like catalase that convert hydrogen peroxide into water and oxygen, preventing cellular damage.

Vacuoles

  • Store water, nutrients, and waste material within the cell. In plant cells, a large central vacuole helps maintain turgor pressure, supporting cell structure.

  • In some protists, vacuoles can also serve as contractile vacuoles, regulating water balance.

Cytoskeleton

  • Provides structural support, facilitates intracellular transport, and is involved in cell motility. It is made of three main components: microfilaments, intermediate filaments, and microtubules.

Microtubules

  • Components of the cytoskeleton; form spindle fibers during cell division and are essential for the structure of cilia and flagella, aiding in cell movement and transport.

  • Serve as tracks for the movement of organelles and vesicles within the cell.

Centrioles

  • Organizes microtubules for cell division, specifically during mitosis, where they help form the spindle apparatus that separates chromosomes.

  • Typically found in pairs within the centrosome, they are cylindrical structures made of microtubules.

Plasma Membrane

  • A selectively permeable barrier that regulates the movement of substances in and out of the cell, maintaining homeostasis.

  • Composed of a lipid bilayer with embedded proteins that assist in transport and communication.

Passive Transport

  • Movement of molecules across a membrane without the use of ATP; relies on concentration gradients.

Simple Diffusion

  • Movement of small, nonpolar molecules (e.g., O₂, CO₂) from areas of high concentration to low concentration until equilibrium is reached.

Facilitated Diffusion

  • Utilizes transport proteins to move larger or charged molecules (e.g., glucose, ions) across the plasma membrane without ATP.

Osmosis

  • Specifically refers to the movement of water across a selectively permeable membrane, driven by water potential gradients.

Hypotonic

  • A solution with a lower concentration of solute compared to the cell; water moves into the cell, potentially causing it to swell and burst.

Hypertonic

  • A solution with a higher concentration of solute compared to the cell; water moves out of the cell, leading to shrinkage.

Isotonic

  • A solution where the concentration of solutes is equal inside and outside the cell; no net movement of water occurs.

Active Transport

  • Requires ATP to move substances against their concentration gradient, ensuring proper cellular function.

Sodium-Potassium Pump

  • An essential active transport mechanism that moves 3 Na⁺ ions out of the cell and brings 2 K⁺ ions in, critical for maintaining the electrochemical gradient across the plasma membrane, crucial for nerve signaling and muscle contraction.

Endocytosis

  • A process through which cells engulf materials via vesicle formation from the plasma membrane, allowing for the uptake of larger particles that cannot pass through the plasma membrane directly.

Phagocytosis

  • Often termed "cell eating," this process involves the engulfing of large particles or even whole cells (e.g., macrophages engulfing bacteria) forming a phagosome.

Pinocytosis

  • Known as "cell drinking," this involves the ingestion of droplets of extracellular fluid and dissolved solutes, allowing cells to sample their environment.

Receptor-Mediated Endocytosis

  • A more selective form of endocytosis where specific molecules bind to receptors on the cell surface, triggering vesicle formation to internalize the bound substances.

Exocytosis

  • A process where vesicles containing substances fuse with the plasma membrane to release their contents outside the cell, assisting in secretion and the expulsion of waste products.

DNA Replication

  • Follows a semi-conservative model where each new DNA molecule consists of one parent strand and one newly synthesized strand; occurs during the S phase of interphase.

Helicase

  • The enzyme responsible for unwinding and separating the two strands of the DNA double helix during replication.

Primase

  • Synthesizes short RNA primers that are necessary to provide a starting point for DNA synthesis.

DNA Polymerase III

  • Main enzyme that adds complementary nucleotides in the 5' to 3' direction during DNA synthesis, ensuring accurate replication of the genetic material.

DNA Polymerase I

  • Removes RNA primers from the newly synthesized DNA strand and replaces them with DNA nucleotides, aiding in proofing the newly formed DNA.

Ligase

  • Seals gaps between Okazaki fragments on the lagging strand, ensuring a continuous DNA molecule is formed by forming phosphodiester bonds.

Topoisomerase

  • Prevents supercoiling of DNA during replication by cutting the DNA strands, allowing them to unwind and rejoining them afterward.

Transcription

  • The process by which the genetic information encoded in DNA is transcribed into messenger RNA (mRNA); occurs in the nucleus in eukaryotes and in the cytoplasm in prokaryotes.

Initiation (Transcription)

  • RNA polymerase binds to the promoter region of a gene, initiating the unwinding of DNA at the transcription start site.

Elongation (Transcription)

  • The RNA polymerase synthesizes the mRNA strand by adding complementary RNA nucleotides, elongating the mRNA transcript.

Termination (Transcription)

  • Transcription concludes when RNA polymerase reaches a terminator sequence, prompting the release of the newly synthesized mRNA molecule.

Translation

  • The process of synthesizing proteins from mRNA at the ribosome; it involves interpretation of codons in mRNA to assemble amino acids into polypeptides.

Initiation (Translation)

  • The ribosome assembles on the mRNA molecule at the start codon (AUG), with the first tRNA carrying methionine (the first amino acid).

Elongation (Translation)

  • tRNA molecules transport specific amino acids to the ribosome, matching their anticodons with mRNA codons, allowing for the elongation of the growing polypeptide chain.

Termination (Translation)

  • Polypeptide synthesis stops when a stop codon is reached; the completed polypeptide is released from the ribosome, folding into its functional form.

Law of Segregation

  • Every individual carries two alleles for each trait, and these alleles segregate during gamete formation, ensuring that each gamete receives only one allele from each parent.

Law of Independent Assortment

  • Genes for different traits assort independently of one another during gamete formation, allowing for genetic variation among offspring.

Incomplete Dominance

  • A genetic phenomenon where the phenotype of a heterozygote is intermediate between the phenotypes of two homozygotes (e.g., crossing red and white flowers resulting in pink flowers).

Codominance

  • A genetic scenario where both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits (e.g., blood type AB).

Polygenic Traits

  • Traits that are influenced by multiple genes, resulting in a continuum of phenotypes (e.g., human skin color and height).

Epistasis

  • The interaction between genes where one gene can mask or suppress the expression of another gene, significantly affecting phenotypic outcomes.

Tundra

  • A biome characterized by cold temperatures, a short growing season, and low biodiversity consisting mainly of mosses, lichens, and some hardy plants.

Desert

  • A biome defined by its extreme dryness and temperature variances, with specialized flora and fauna adapted to moisture scarcity.

Tropical Rainforest

  • A biome with high biodiversity, warm temperatures year-round, and heavy rainfall, supporting dense vegetation and a vast array of wildlife.

Producers (Autotrophs)

  • Organisms, primarily plants, that convert sunlight into chemical energy via photosynthesis, forming the base of the food chain.

Primary Consumers

  • Herbivores that directly consume producers, playing a critical role in energy transfer within the ecosystem.

Secondary Consumers

  • Carnivores that feed on primary consumers, serving as a bridge in energy transfer up the food chain.

Tertiary Consumers

  • Apex predators that occupy the top of the food chain, preying on secondary consumers, and maintaining ecological balance.

Decomposers

  • Organisms like fungi and bacteria that break down dead organic matter, recycling nutrients back into the ecosystem and playing an essential role in nutrient cycling.

Exponential Growth

  • Characterized by a J-shaped curve on a graph, indicating rapid population growth when resources are unlimited.

Logistic Growth

  • An S-shaped curve representing population growth that stabilizes at an environmental carrying capacity due to resource limitations.

C3 Plants

  • Utilize the normal Calvin cycle for photosynthesis; they thrive in moderate climates and include crops like wheat and rice.

C4 Plants

  • Adapted for hot and dry environments, C4 plants reduce photorespiration and improve efficiency of CO2 capture, including species like corn and sugarcane.

CAM Plants

  • Adapted to conserve water by opening stomata at night to take in CO2, which is then used for photosynthesis during the day. Common examples are cacti and succulents.

Auxins

  • A class of plant hormones that promote cell elongation, influencing growth toward light (phototropism) and gravity (gravitropism).

Gibberellins

  • Plant hormones that stimulate various growth processes such as seed germination, stem elongation, and flowering.

Cytokinins

  • Hormones that promote cell division, affecting growth and development processes in plants, particularly in roots and shoots.

Ethylene

  • A gaseous hormone that regulates fruit ripening and promotes senescence, triggering processes like leaf abscission and flower wilting.

Intracellular Signaling Pathways: These are communication routes cells use to respond to stimuli. First, a ligand (signal molecule) binds a receptor on the cell surface. This triggers a cascade (transduction), often involving second messengers like cAMP. The signal is amplified and leads to a specific cellular response, such as gene expression or enzyme activation.

Metabolism: Metabolism is all the chemical reactions in a cell. Anabolic pathways build complex molecules (e.g., making proteins from amino acids) and require energy. Catabolic pathways break down molecules (e.g., glucose breakdown in respiration) and release energy. ATP is the energy currency that links these reactions.

Citric Acid Cycle (Krebs Cycle): Occurs in the mitochondrial matrix. Acetyl-CoA enters the cycle, producing 3 NADH, 1 FADH2, 1 ATP (or GTP), and 2 CO2 per turn. NADH and FADH2 carry electrons to the electron transport chain. This cycle is central to aerobic respiration.

G1-S Transition: A checkpoint where the cell decides whether to begin DNA replication. Controlled by cyclins and CDKs. If conditions are favorable (enough nutrients, no DNA damage), the cell moves to S phase. If not, the cycle halts, preventing damaged DNA from being copied.

Mitosis vs. Meiosis: Mitosis results in two identical diploid cells (used in growth/repair). Meiosis produces four non-identical haploid cells (gametes) with half the DNA. Meiosis includes crossing over and independent assortment, increasing genetic variation.

Signal Transduction: A detailed example is the epinephrine (adrenaline) response. Epinephrine binds a G-protein coupled receptor, activating adenylate cyclase, which turns ATP into cAMP. cAMP activates protein kinase A, triggering glucose release from glycogen. This shows how a small signal is amplified to create a large response.

Hardy-Weinberg Equilibrium: Used to determine if a population is evolving. If allele/genotype frequencies remain constant over generations, the population is in equilibrium. The five conditions are: no mutations, random mating, no natural selection, large population, and no gene flow. Deviations suggest evolution.

Phylogenetic Trees: Show evolutionary relationships. Branch points (nodes) represent common ancestors. The closer two species are on a tree, the more recently they shared an ancestor. Trees are built using morphological traits and molecular data.

Purines/Pyrimidines: Purines (adenine, guanine) are larger, double-ringed bases. Pyrimidines (cytosine, thymine in DNA; uracil in RNA) are single-ringed. A pairs with T (or U in RNA), and G pairs with C through hydrogen bonds. These base pairings are key to DNA structure and replication.

Cells: Cells are the basic units of life. There are two main types: prokaryotic (bacteria and archaea) and eukaryotic (plants, animals, fungi, protists). Eukaryotic cells have membrane-bound organelles. You should be able to identify and describe organelles like the nucleus (stores DNA), mitochondria (produces ATP), rough ER (makes proteins), smooth ER (makes lipids), Golgi apparatus (packages and modifies proteins), lysosomes (digestive enzymes), and chloroplasts (in plants, for photosynthesis).

Membranes: The plasma membrane is composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates. This structure is described by the "fluid mosaic model" because components move fluidly. It controls what enters and exits the cell. Proteins serve as channels, receptors, or enzymes. Cholesterol stabilizes the membrane. Carbohydrates help with cell recognition.

Prokaryotic Types:

  • Bacteria: Common, diverse, include pathogens and decomposers.

  • Archaea: Live in extreme environments (high heat, salt, acidity), genetically distinct from bacteria.

Trophic Strategies:

Autotrophs:
Produce their own food (e.g., plants via photosynthesis).

Heterotrophs:
Consume other organisms for energy.

Chemoautotrophs:
Use chemicals (not light) as an energy source and make their own food (e.g., bacteria near hydrothermal vents).

Chemoheterotrophs:
Use chemicals for energy and must consume organic compounds (e.g., humans).

Purines & Pyrimidines:

Purines:

  • Double-ring nitrogenous bases

  • Adenine (A) and Guanine (G)

Pyrimidines:

  • Single-ring bases

  • Cytosine (C), Thymine (T) (DNA only), and Uracil (U) (RNA only)

Phylogenetic Tree & Phylogeny:

Illustrate evolutionary relationships.

  • Nodes = common ancestors

  • Branches = evolutionary paths

  • The closer two organisms are on the tree, the more recently they shared a common ancestor.

    Hardy-Weinberg Equilibrium:

    Describes a non-evolving population. Conditions: no mutation, random mating, no gene flow, large population, and no natural selection.

    Equations:

    • p + q = 1 (allele frequency)

    • p² + 2pq + q² = 1 (genotype frequency)

    Where:

    • p = frequency of dominant allele

    • q = frequency of recessive allele

    Allele Frequency Review:

    p = # of dominant alleles / total alleles
    q = # of recessive alleles / total alleles

    Iridium in Meteorites:

    Iridium is rare on Earth but common in meteorites. A layer rich in iridium supports the theory that a meteor impact led to the dinosaur extinction (K-T boundary).

    Pangaea:

    A supercontinent that existed during the late Paleozoic and early Mesozoic eras. Its breakup influenced species distribution and evolution.

  • DNA and RNA are nucleic acids made of nucleotide monomers. Each nucleotide contains a sugar, phosphate group, and nitrogenous base.

    Central Dogma:

    The flow of genetic information:
    DNA → RNA → Protein
    DNA is transcribed into RNA, which is then translated into protein.

Catabolic Reactions:
Break down molecules and release energy (e.g., cellular respiration).

Anabolic Reactions:
Build molecules and require energy (e.g., photosynthesis, protein synthesis).

Exergonic:
Energy-releasing reactions (ΔG is negative).

Endergonic:
Require energy input (ΔG is positive).

Enzymes:

Biological catalysts that speed up reactions by lowering activation energy.

  • Competitive inhibitors: Bind to active site.

  • Noncompetitive inhibitors: Bind to another site, changing enzyme shape.

Feedback inhibition:
A method of metabolic control where the end product inhibits an earlier enzyme in the pathway to prevent overproduction.

What is Biology?

Biology is the scientific study of life and living organisms, including their structure, function, growth, evolution, distribution, and taxonomy.

Amino Acids

Building blocks of proteins. Each amino acid contains an amino group, carboxyl group, hydrogen, and an R-group (side chain). There are 20 different types.

Structure of Proteins (4 Levels):

  1. Primary: Linear sequence of amino acids.

  2. Secondary: Local folding (alpha helices and beta sheets) stabilized by hydrogen bonds.

  3. Tertiary: 3D shape of the protein due to interactions among R-groups.

  4. Quaternary: Multiple polypeptides coming together (e.g., hemoglobin).

Lipids:

Hydrophobic macromolecules, including fats, oils, phospholipids, and steroids. Used for energy storage, insulation, and cell membrane structure.

DNA:
Stores genetic information. Transcribed into RNA during gene expression.

mRNA (Messenger RNA):
Carries the genetic message from DNA in the nucleus to the ribosome for translation.

tRNA (Transfer RNA):
Brings the correct amino acid to the ribosome during protein synthesis.

rRNA (Ribosomal RNA):
Structural and enzymatic component of the ribosome. Helps catalyze the formation of peptide bonds.

Central Dogma:
DNA → RNA → Protein

Enzymes

Enzymes:
Biological catalysts that speed up chemical reactions by lowering activation energy. They are not consumed in the reaction and are specific to their substrates.

Mitosis (PMAT)

Mnemonic: “Please Make A Taco”

  • P – Prophase: Chromosomes condense, spindle fibers begin to form, nuclear envelope breaks down.

  • M – Metaphase: Chromosomes align in the middle of the cell.

  • A – Anaphase: Sister chromatids are pulled apart to opposite poles.

  • T – Telophase: Two nuclei start forming, chromosomes decondense, and the spindle breaks down.

  • (I) – Interphase: Not part of mitosis but important; the cell grows and prepares for division (G1, S, G2 phases).

Cytokinesis:
Division of the cytoplasm. Follows telophase and completes cell division.

Cell Cycle Phases

Mnemonic: “Go Sally Go! Make A Twin Cell!”

  • G1 (Gap 1): Cell grows in size and synthesizes proteins.

  • S (Synthesis): DNA replication occurs.

  • G2 (Gap 2): Final preparations for mitosis; growth and error-checking.

  • M (Mitosis): Cell divides its nucleus and chromosomes.

  • C (Cytokinesis): Cell splits into two daughter cells.

Cell Signaling

Mnemonic: “A Pirate Eats Jelly”

  • A – Autocrine: Cell signals itself (self-signaling).

  • P – Paracrine: Signals to nearby cells (short-range).

  • E – Endocrine: Signals to distant cells through the bloodstream (e.g., hormones).

  • J – Juxtacrine: Direct cell-to-cell contact signaling (requires physical contact).

    Intermediate Filaments:
    Provide structural support and help maintain cell shape. They are more permanent than microfilaments or microtubules.

    Actin (Microfilaments):
    Support cell shape, assist with cell movement, and are involved in cytokinesis during cell division.

    Microtubules:
    Hollow tubes involved in intracellular transport (like vesicle movement), cilia/flagella movement, and mitosis.

  • Centrosome/Centrioles:
    Organize microtubules during cell division (mitosis and meiosis) and help form the spindle fibers.

    Plasmids:
    Small circular DNA molecules found in prokaryotes (especially bacteria). They can carry genes like antibiotic resistance and can be shared between bacteria through conjugation.

  • Cell Membrane: A phospholipid bilayer that protects the cell, regulates the movement of substances in and out, and facilitates communication between cells through receptors.

  • Dihybrid Cross Example: Crossing TtYy x TtYy gives you a 9:3:3:1 ratio of phenotypes (tall-yellow, tall-green, dwarf-yellow, dwarf-green).

  • Law of Segregation: During gamete formation (sperm and egg), the two alleles for a gene separate so that each gamete only gets one. For example, a Tt individual produces gametes with either T or t.

  • Law of Independent Assortment: Genes located on different chromosomes are inherited independently of each other. This means inheritance of seed shape doesn't affect inheritance of seed color. A cross between TtYy x TtYy yields a 9:3:3:1 ratio of phenotypes in offspring.

  • Mendelian Inheritance Patterns

  • Simple Dominance: One allele (dominant) masks the other (recessive). TT and Tt both show the dominant trait.

  • Incomplete Dominance: Heterozygotes have a blended phenotype. Red (RR) x White (rr) → Pink (Rr).

  • Codominance: Both alleles are fully expressed in heterozygotes. Example: Blood type AB (A and B both expressed).

  • Incomplete Penetrance: A person has the dominant allele but doesn’t show the trait due to other genetic/environmental factors (e.g., not all people with the polydactyly gene have extra fingers).

  • Overdominance: Heterozygote is more fit than either homozygote. Example: Sickle cell trait protects against malaria.

  • X-linked Inheritance: Traits from genes on the X chromosome. Males (XY) show X-linked recessive traits more often because they only have one X (e.g., color blindness).

3. Inheritance Patterns Involving Two Genes

  • Epistasis: One gene can suppress or hide the expression of another gene. Example: In flowers, cc = white regardless of pigment gene.

  • Complementation: Two individuals with mutations in different genes produce normal offspring because each supplies the missing function.

  • Gene Modifier Effect: One gene modifies how another gene is expressed (e.g., a gene that darkens coat color).

  • Gene Redundancy: Two genes can perform the same function. If one is mutated, the other compensates. Only when both are mutated does a phenotype appear.

4. Population Genetics Basics

  • Allele Frequency: Proportion of each allele in the population. For 100 individuals with 64 GG, 32 Gg, 4 gg:

    • g = (32 + 2×4)/200 = 0.2

    • G = 1 − 0.2 = 0.8

  • Genotype Frequency: Proportion of GG, Gg, and gg individuals in the population.

    • GG = 64/100 = 0.64; Gg = 32/100 = 0.32; gg = 4/100 = 0.04

5. Hardy-Weinberg Principle

  • Describes a non-evolving population where allele frequencies remain constant.

  • Equation: p² + 2pq + q² = 1

    • p = frequency of dominant allele, q = frequency of recessive allele

    • p² = frequency of homozygous dominant

    • 2pq = heterozygous

    • q² = homozygous recessive

  • Assumptions: No mutations, random mating, no gene flow, large population, no natural selection

6. Probability in Genetics

  • Sum Rule: Add probabilities of mutually exclusive events (e.g., probability of A OR B happening).

  • Product Rule: Multiply probabilities of independent events (e.g., A AND B both happening).

  • Binomial Expansion: Calculates probabilities of unordered events. Used to predict outcomes in cases like: "What’s the chance 2 out of 5 kids have blue eyes?"

7. Plant Biology Overview

  • Plastids:

    • Chloroplasts: Photosynthesis (contain thylakoids and stroma)

    • Chromoplasts: Pigment storage (colors in fruits and flowers)

    • Leucoplasts: Store starch, lipids, or proteins

  • Cell Wall: Rigid outer layer made of cellulose that supports the plant cell

  • Central Vacuole: Stores water and contributes to turgor pressure (keeps the plant upright)

  • Photosynthesis:

    • Equation: CO₂ + H₂O + light → glucose + O₂

    • Light Reactions (in thylakoids): Use light to make ATP and NADPH

    • Calvin Cycle (in stroma): Uses ATP/NADPH to fix carbon into sugars

Tissue Types:

  • Ground Tissue: Photosynthesis and storage (parenchyma, collenchyma, sclerenchyma)

  • Vascular Tissue: Xylem (water) and Phloem (sugars)

  • Dermal Tissue: Outer protective layer (epidermis, sometimes waxy cuticle)

Microbiology Essentials

Gram Stain:

  • Gram-positive: Thick peptidoglycan wall, stains purple

  • Gram-negative: Thin wall, outer membrane with LPS, stains pink

Bacterial Cell Structures:

  • Shapes: Coccus (round), Bacillus (rod), Spiral (spirillum, spirochete)

  • Flagella: Movement

  • Pili/Fimbriae: Attachment and DNA transfer (conjugation)

  • Capsule: Sticky layer for protection

Enzyme Structure:

  • Apoenzyme: Protein part (inactive alone)

  • Cofactor/Coenzyme: Non-protein helper (metal ions or vitamins)

  • Holoenzyme: Active enzyme with cofactor

  • Enzyme function depends on pH, temp, and substrate concentration

Osmosis in Bacteria:

  • Hypertonic: Water leaves cell → shrinks (plasmolysis)

  • Hypotonic: Water enters → may burst (lysis)

  • Isotonic: No net movement

Cellular Respiration Summary:

  • Glycolysis: Glucose → pyruvate (makes 2 ATP, 2 NADH)

  • Krebs Cycle: Pyruvate → Acetyl-CoA → CO₂ + NADH + FADH₂

  • ETC: Electrons from NADH/FADH₂ power ATP synthesis via chemiosmosis (makes ~34 ATP)

  • Fermentation: Without oxygen, pyruvate becomes lactic acid or alcohol; regenerates NAD⁺

Bacterial Growth Curve:

  1. Lag Phase: No division; cells prepare

  2. Log Phase: Rapid division

  3. Stationary Phase: Nutrients limited; growth = death

  4. Death Phase: More cells die than divide

Microbial Control Methods:

  • Autoclaving: Sterilizes with pressurized steam

  • Filtration: For heat-sensitive solutions

  • Pasteurization: Kills pathogens without spoiling food

Genetic Transfer in Bacteria:

  • Transformation: Bacteria absorb naked DNA from environment

  • Conjugation: Transfer via pilus from one bacterium to another

  • Transduction: Transfer of DNA via bacteriophage (virus)

PCR (Polymerase Chain Reaction): Amplifies DNA using special enzymes (like Taq polymerase)

Kirby-Bauer Antibiotic Test: Discs with antibiotics placed on a bacterial culture. Larger clear zones = more effective drug.