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Cell Structure & Fun
| Question | Answer |
|---|---|
| Cell Envelope: | consists of a series of layered structures that surround the cytoplasm and govern cellular interactions with the external environment. |
| Cytoplasmic Membrane: | surrounds cytoplasm (mixture of macromolecules and small molecules), separates it from environment. Main function is selective permeability (nutrients transported in and waste products out). |
| Phospholipid Structure | have both hydrophobic (water-repelling) components, which are fatty acid tails, and hydrophilic (water-attracting) components, which are glycerophosphate + functional groups (sugars, ethanolamine, or choline) |
| Bilayer Architecture | Lipid bilayer or unit membrane structure, Fatty acid tails associate to form hydrophobic region, Head groups exposed to environment (outer surface) and cytoplasm (inner surface). |
| Integral membrane proteins | Significantly embedded in the membrane. Some integral proteins are called transmembrane proteins, which extend completely across the membrane. Have hydrophobic domains spanning membrane and hydrophilic domains contacting environment/cytoplasm. |
| Peripheral membrane proteins | More loosely attached. Some are lipoproteins, which contain hydrophobic lipid tails that anchor proteins to the membrane. Associate with head groups or other membrane proteins. |
| Differences Between Eukaryotic/Bacterial Cytoplasmic Membranes Vs. Archaic Membranes: | In B and E the hydrophobic fatty acid tails are bound to glycerol by ester linkages; the lipids of Archaea have hydrophobic isoprenoid (rather than fatty acid) tails, which are bound to glycerol by ether bonds. |
| Major Functions of the Cytoplasmic Membrane include… | permability barrier, protein anchoring, energy conservation and consumption. |
| Permeability Barrier (Function of Cytoplasmic Membrane): | Prevents passive leakage of solutes, Barrier to diffusion of most substances, especially polar or charged molecules, Most substances must be carried by transport proteins |
| Protein Anchoring (Function of Cytoplasmic Membrane): | site of proteins that participate in transport, bioenergetics, and chemotaxis. |
| Energy Conservation and Consumption (Function of Cytoplasmic Membrane): | site of generation and dissipation of the proton motive force. |
| Mitochondrion: | performs energy conversation with respiration |
| Chloroplast: | performs energy conservation with photosynthesis |
| Simple Transport Systems Structure: | Single transmembrane transport protein, Contains ~12 domains that weave through membrane forming a channel, Conformational change occurs when binding specific solute (like a gate opening) |
| Glycan Tetrapeptide: | glycan chains connected by tetrapeptide cross-links in bacterial peptidoglycan, a polymer vital for cell wall integrity. |
| Symport Transport: | Solute + proton transported in same direction |
| Antiport Transport: | Solute + proton transported in opposite directions |
| Prokaryotic Cell Walls Functions: | osmotic protection, prevents cell lysis, maintains shape, location |
| Osmotic Protection (Prokaryotic Cell Wall Functions): | Cytoplasm maintains ~2 atm pressure (same as car tire) |
| Prevents Cell Lysis (Prokaryotic Cell Wall Functions): | Without cell wall, osmotic pressure would burst membrane |
| Maintains Shape (Prokaryotic Cell Wall Functions): | Provides structural rigidity and cell shape |
| Location (Prokaryotic Cell Wall Functions): | Layer outside cytoplasmic membrane |
| Gram-Positive Bacteria Structure: | Thick peptoglycan layer (90% of the cell wall, teichoic acids, and lipoteichoic acids). Stains purple. |
| Gram-Negative Bacteria Structure: | Thin peptidoglycan layer, outer membrane containing LPS in the outer leaflet and phospholipids in the inner layer. Stains pink. |
| Archaeal Cell Walls’s Differences From Bacteria: | No peptidoglycan (unique to Bacteria), usually no outer membrane, gram stain not useful for classification, most have S-layer instead of polysaccharide wall |
| Label the Structure of the Cytoplasmic Membrane: | -- |
| Lysozyme (Natural Defense): | Cleaves N-acetylglucosamine—N-acetylmuramic acid bonds, comes from human tears, saliva, body fluids. Weakens peptidoglycan → cell lysis. Only works on Bacteria (not Archaea) |
| Antibiotics (e.g., Penicillin): | Blocks new cross-links during cell wall synthesis. Compromises wall strength → cell lysis. Human cells lack cell walls, so not affected |
| LPS and The Outer Membrane: | Location: External to cell wall in gram-negative bacteria. Most of the outer membrane's cell wall is composed of lipopolysaccharide (LPS) Key Feature: Contains lipopolysaccharide (LPS) - polysaccharides covalently bound to lipids |
| Functions of LPS (Structural): | Surface Recognition: Cell identification Mechanical Strength: Contributes to cell envelope integrity Ionic Bonding: Adjacent LPS molecules linked by divalent cations (Ca²⁺, Mg²⁺) |
| Functions of LPS (Pathogenic) | Virulence Factor: Important for bacterial pathogenicity Endotoxin Activity: Lipid A component specifically toxic |
| Periplasm: | Between cytoplasmic membrane outer membrane, contained space for extracellular proteins. |
| Porins: | Outer Membrane Channels, Unique to bacterial outer membrane, |
| Nonspecific Porins: | Form water-filled channels, Allow passage of very small hydrophilic substances, General permeability function |
| Specific Porins: | Contain binding sites for specific substrates, Selective for one or group of structurally related substances, More controlled transport |
| Important Distinction Between Porin Types: | Porins: Bacterial outer membrane (solute transport) Aquaporins: Different class, cytoplasmic membrane (water transport) |
| Bacteria Cell Membrane Vs. Archaeal Cell Membrane: | latter has ester bonds (less stable), straight-chain fatty acids, always bilayer, Archael has ether bonds (more stable), branched isoprenoid chains, can be bilayer or monolayer |
| Peptidoglycan Structure (Detailed): | glycan backbone with alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Cross-linking peptides with L-alanine, D-glutamic acid, etc. Cross-links between peptides provide strength. |
| β-1,4 glycosidic bonds | Connect sugar units in the glycan backbone |
| Transpeptidation: | Process that creates cross-links between peptidoglycan peptide chains. |
| Lipid A (LPS Structure Components): | Hydrophobic anchor embedded in outer membrane, has endotoxic activity |
| Pyrogen (LPS): | Causes fever by stimulating cytokine release |
| Septic shock (LPS): | Massive LPS release can cause life-threatening systemic inflammation |
| Antibiotic complications (LPS): | Cell death releases more LPS, potentially worsening symptoms |
| Explain the Archaeal Cell Walls’s Pseudomurein Structure (found in methanogens): | Similar structure to peptidoglycan but with differences → alternating N-acetylglucosamine and N-acetyltalosaminuronic acid, β-1,3 glycosidic bonds instead of β-1,4 bonds, All amino acids are L-stereoisomers (unlike the mixed D and L) |
| Explain the Resistance of the Archaeal Cell Walls’s Pseudomurein Structure: | Cannot be destroyed by lysozyme enzyme or penicillin antibiotic, making archaea naturally resistant to many treatments that target bacterial cell walls |
| Capsules and Slime Layers: | These are protective and adhesive structures found on the outside of the cell envelope. |
| Capsules: | Composed of sticky polysaccharide materials, Tightly attached to the cell surface forming a rigid, well-defined matrix. Visible if treated with India ink. |
| Slime Layers: | Loosely attached polysaccharide coatings, Easily deformed and less structured than capsules, Function in adhesion and protection but are more flexible than capsules. (eg. Leuconostoc) |
| Pili: | Thin, filamentous protein structures extending from the cell surface, Enable organisms to adhere to surfaces, other cells, or substrates, Allow formation of pellicles (thin sheets of cells on liquid surfaces) and biofilms. |
| Conjugative/sex pili | Facilitate genetic exchange between bacterial cells through conjugation |
| Electrically conductive pili: | Can conduct electrons, important in certain metabolic processes |
| Fimbriae | Short pili specifically involved in cellular attachment, Produced by all Gram-negative bacteria and many Gram-positive bacteria, Mediate binding to host cells, surfaces, and other bacteria |
| Flagella: | whip-like appendages on microbes and cells that provide locomotion, enabling them to move through their environment. Not all bacterial cells have flagella. |
| Endospores: | Dormant cells that can remain for some time. Present only in certain Gram-positive bacteria. Resistent to harsh conditions like high tempe. Endure unfavorable growth conditions when nutrients become scarce or environmental conditions become hostile |
| Endospore Lifestyle: | Vegetative cell → endospore formation → endospore → germination back to vegetative cell |
| Virulence Factors: | molecules or traits produced by pathogens that contribute to their ability to cause disease in a host. |
| Endospores Are Found: | Present only in certain Gram-positive bacterial groups. Primarily found in the orders Bacillales (including Bacillus species) and Clostridiales (including Clostridium species) |
| Compare and Contrast Between Gram-Positive and Gram-Negative Cell Walls: | Gram-positive: Thick peptidoglycan, no outer membrane, purple after Gram stain. Gram-negative: Thin peptidoglycan, has an outer membrane with LPS, pink after Gram stain. |
| Myco: | this prefix means fungi. |
Created by:
smurtab