Biomembrane Structure Quiz

Biomembrane Structure

• Plasma membranes (PM) are composed of lipid bilayers, proteins, and carbohydrates
• They act as a semi-permeable barrier, controlling substance movement
• The fluid mosaic model describes lateral movement of lipids and proteins within the membrane
• Membrane proteins are categorized as:
  • Integral (transmembrane): Span the bilayer
  • Peripheral: Attached via non-covalent interactions
  • Lipid-anchored: Covalently linked to lipids (e.g., GPI anchors)
• Lipid bilayers have hydrophilic heads facing outward and hydrophobic tails inward
• Cholesterol regulates fluidity and stability
• Membrane lipids include phospholipids (e.g., phosphatidylcholine, phosphatidylserine), sphingolipids (e.g., sphingomyelin, glycolipids, ceramides), and sterols (e.g., cholesterol, phytosterols)
• Membrane asymmetry exists with different lipid compositions in cytosolic vs. extracellular leaflets
• Lipid distribution is regulated by flipases, floppases, and scramblases
• Membranes exhibit self-sealing and fusion properties, facilitating vesicle formation, endocytosis, and exocytosis
• Lateral diffusion allows lipids and proteins to move within the membrane
• Phase transitions (gel to fluid state) depend on temperature
• Lipid rafts are specialized regions enriched with cholesterol and sphingolipids for signaling and trafficking

Transmembrane Transport of Ions and Small Molecules

• Pumps (primary active transport) use ATP to move molecules against gradients
• Channels allow specific ion passage down electrochemical gradients
• Transporters (carriers) undergo conformational changes to move molecules
• Transporter types include:
  • Uniporters: Transport a single molecule down its gradient (e.g., GLUT1 for glucose)
  • Symporters: Move two molecules in the same direction (e.g., Na+/glucose symporter)
  • Antiporters: Move two molecules in opposite directions (e.g., Na+/H+ exchanger)
• ATP-powered transport proteins include:
  • P-class pumps (e.g., Na+/K+ ATPase, Ca2+ ATPase)
  • V-class pumps (acidify organelles)
  • F-class pumps (ATP synthase)
  • ABC transporters (multidrug resistance, CFTR)
• Resting membrane potential is approximately -70 mV, maintained by Na+/K+ ATPase and K+ leak channels
• Voltage-gated ion channels open/close in response to voltage changes (e.g., Na+, K+, Ca2+) for action potentials

Cellular Energetics

• Aerobic respiration uses O2 as the final electron acceptor in the electron transport chain
• Anaerobic respiration uses alternative electron acceptors (e.g., sulfate, nitrate)
• Cellular respiration's overall equation: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 30-32 ATP
• Stages of glucose oxidation include Glycolysis (cytoplasm), Pyruvate oxidation (mitochondrial matrix), Citric Acid Cycle (TCA cycle), and Electron Transport Chain & Oxidative Phosphorylation
• Lipid oxidation (beta-oxidation) breaks down fatty acids into acetyl-CoA, NADH, and FADH2
• Protein catabolism deaminates amino acids, allowing them to enter the TCA cycle
• Photosynthesis involves light-dependent reactions (split water, producing O2 and protons, reducing NADP+ to NADPH) and Calvin cycle (fixing CO2 into glyceraldehyde-3-phosphate (G3P))