BIO 101 Exam 2 Study Guide: Membrane Structure, Metabolism, Cellular Respiration, and Photosynthesis

Chapter 7: Membrane Structure and Function

Fluid Mosaic Model

The fluid mosaic model describes the structure of cell membranes as a mosaic of components—phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.

• Amphipathic molecules: Phospholipids have both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

• Cholesterol: Stabilizes membrane fluidity across temperature changes.

Membrane Proteins

• Integral proteins: Span the membrane; involved in transport, signal transduction, and cell recognition.

• Peripheral proteins: Loosely bound to the membrane surface; often involved in signaling or maintaining cell shape.

• Membrane carbohydrates: Usually attached to proteins or lipids (glycoproteins/glycolipids); play roles in cell recognition.

Selective Permeability

• The membrane allows some substances to cross more easily than others.

• Passes easily: Small, nonpolar molecules (e.g., O2, CO2).

• Needs help: Ions and large polar molecules require transport proteins.

Transport Proteins

• Channel proteins: Provide corridors for specific molecules or ions to cross.

• Carrier proteins: Bind to molecules and change shape to shuttle them across the membrane.

Passive Transport

• Diffusion: Movement of molecules from high to low concentration.

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Tonicity: The ability of a solution to cause a cell to gain or lose water.

• Isotonic: No net water movement.

• Hypertonic: Cell loses water.

• Hypotonic: Cell gains water.

• Osmoregulation: Control of water balance (important in unicellular organisms).

• Plant cells: Prefer hypotonic solutions (turgid).

• Red blood cells: Lyse in hypotonic, crenate in hypertonic solutions.

Facilitated Diffusion

• Transport proteins help substances move down their concentration gradient without energy input.

Active Transport

• Moves substances against their concentration gradient; requires energy (usually ATP).

• Sodium/Potassium pump: Pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed.

Bulk Transport

• Endocytosis: Cell takes in macromolecules by forming vesicles.

  • Phagocytosis: "Cell eating" (solids).

  • Pinocytosis: "Cell drinking" (liquids).

  • Receptor-mediated endocytosis: Specific uptake using receptors.

• Exocytosis: Vesicles fuse with membrane to release contents outside the cell.

Chapter 8: Metabolism

Metabolic Pathways

Metabolism is the sum of all chemical reactions in an organism, organized into pathways.

• Catabolic pathways: Break down molecules, releasing energy (e.g., cellular respiration).

• Anabolic pathways: Build complex molecules, consuming energy (e.g., protein synthesis).

Energy and Thermodynamics

• Types of energy: Kinetic (motion), potential (position), chemical (stored in bonds).

• First law: Energy cannot be created or destroyed, only transformed.

• Second law: Every energy transfer increases entropy (disorder) of the universe.

• Entropy (S): Measure of disorder.

Free Energy and Reactions

• Exergonic reactions: Release free energy; spontaneous.

• Endergonic reactions: Absorb free energy; nonspontaneous.

• Free energy change:

$\Delta G = \Delta H - T\Delta S$

• ATP: Main energy currency; hydrolysis releases energy for cellular work.

• Energy coupling: Using exergonic processes to drive endergonic ones.

• ATP regeneration: ATP is regenerated from ADP and Pi by cellular respiration.

Enzymes and Catalysis

• Enzymes: Biological catalysts that lower activation energy.

• Activation energy (Ea): Energy needed to start a reaction.

• Substrate: Reactant that an enzyme acts on.

• Enzyme-substrate complex: Temporary binding of enzyme and substrate.

• Active site: Region on enzyme where substrate binds.

• Specificity: Each enzyme acts on a specific substrate.

• Induced fit: Enzyme changes shape to fit substrate more closely.

• Effect of temperature and pH: Each enzyme has optimal conditions; extremes can denature enzymes.

• Cofactors: Nonprotein helpers (e.g., metal ions, vitamins).

• Inhibitors:

  • Competitive: Bind active site, blocking substrate.

  • Noncompetitive: Bind elsewhere, changing enzyme shape.

Chapter 9: Cellular Respiration and Fermentation

Overview and Formula

• Cellular respiration is the process by which cells extract energy from glucose.

• Overall equation:

$\mathrm{C_6H_{12}O_6} + 6\,\mathrm{O_2} \rightarrow 6\,\mathrm{CO_2} + 6\,\mathrm{H_2O} + \text{energy (ATP + heat)}$

• Redox reactions: Transfer of electrons; oxidation (loss), reduction (gain).

Stages of Cellular Respiration

1. Glycolysis: Occurs in cytosol; does not require oxygen; splits glucose into 2 pyruvate; net gain: 2 ATP, 2 NADH.

   • Energy investment phase: Uses 2 ATP.

   • Energy payoff phase: Produces 4 ATP (net 2 ATP).

2. Citric Acid Cycle (Krebs Cycle): Occurs in mitochondrial matrix; requires oxygen indirectly; pyruvate oxidized to acetyl-CoA; each glucose yields 2 turns; net products per glucose: 6 NADH, 2 FADH2, 2 ATP, 4 CO2.

3. Oxidative Phosphorylation: Occurs in inner mitochondrial membrane; includes electron transport chain (ETC) and chemiosmosis.

   • ETC: Electrons from NADH and FADH2 pass through protein complexes, pumping H+ to create a gradient.

   • Chemiosmosis: H+ flows back through ATP synthase, driving ATP production.

   • Net ATP yield: About 30-32 ATP per glucose (aerobic).

Fermentation

• Occurs when oxygen is absent; glycolysis continues, but pyruvate is converted to waste products.

• Lactic acid fermentation: Pyruvate reduced to lactate (e.g., muscle cells).

• Alcohol fermentation: Pyruvate converted to ethanol and CO2 (e.g., yeast).

Chapter 10: Photosynthesis

Overview and Formula

• Photosynthesis converts light energy into chemical energy in plants, algae, and some bacteria.

• Overall equation:

$6\,\mathrm{CO_2} + 6\,\mathrm{H_2O} + \text{light energy} \rightarrow \mathrm{C_6H_{12}O_6} + 6\,\mathrm{O_2}$

• Autotrophs: Organisms that produce their own food (producers).

• Heterotrophs: Obtain food by consuming other organisms (consumers).

Chloroplast Structure

• Mesophyll: Leaf cells where most photosynthesis occurs.

• Stomata: Pores for gas exchange.

• Thylakoids: Membranous sacs; site of light reactions.

• Grana: Stacks of thylakoids.

• Chlorophyll: Main pigment absorbing light energy.

Stages of Photosynthesis

1. Light Reactions: Occur in thylakoid membranes; convert light energy to chemical energy (ATP, NADPH); O2 released.

   • Reactants: H2O, light, NADP+, ADP + Pi.

   • Products: O2, ATP, NADPH.

   • ATP and NADPH proceed to Calvin cycle.

2. Calvin Cycle: Occurs in stroma; uses ATP and NADPH to convert CO2 to G3P (sugar).

   • Three phases:

     • Carbon fixation: CO2 attached to RuBP by rubisco.

     • Reduction: ATP and NADPH reduce 3-phosphoglycerate to G3P.

     • Regeneration: RuBP regenerated for next cycle.

Light Absorption and Photosystems

• Electromagnetic spectrum: Range of all light wavelengths; visible light used in photosynthesis.

• Chlorophyll a and b: Absorb different wavelengths for maximum efficiency.

• Photosystem II (PSII): Functions first; splits water, releases O2.

• Photosystem I (PSI): Functions second; produces NADPH.

• Cyclic electron flow: Only PSI; produces ATP but not NADPH or O2.

Photorespiration and Plant Adaptations

• Photorespiration: Rubisco adds O2 instead of CO2, reducing efficiency.

• C4 plants: Spatial separation of steps; CO2 fixed in mesophyll, Calvin cycle in bundle-sheath cells.

• CAM plants: Temporal separation; CO2 fixed at night, Calvin cycle during day.