Crush AP Bio Unit 3! Enzymes, Photosynthesis and Respiration

Overview of AP Bio Unit 3: Cellular Energetics

  • Preparation for tough unit covering cellular respiration and photosynthesis.

  • Video aims to teach key concepts for success in exams.

  • Covered topics:

    • Enzymes

    • Cellular energy & ATP

    • Photosynthesis (big picture, light reactions, Calvin cycle)

    • Cellular respiration (glycolysis, link reaction, Krebs cycle, electron transport chain)

Topics 3.1 to 3.3: Enzymes

Key Properties of Enzymes

  • Enzymes: proteins or RNAs that catalyze reactions by lowering activation energy.

  • Enzyme-catalyzed reactions have lower activation energy compared to non-enzyme-catalyzed reactions.

  • Enzymes are highly specific, fitting substrates in a tailored active site.

Structure and Function

  • Enzymes have complex secondary, tertiary, and quaternary structures held together by:

    • Hydrogen bonds

    • Ionic bonds

    • Hydrophobic interactions

  • Temperature, pH, and ion concentration can denature enzymes, changing active site shape and reducing function.

  • Optimum conditions promote best binding and activity.

Effects of Environmental Changes

pH

  • Enzyme function peaks at specific pH.

  • Deviations (too high/low) lead to decreased activity due to denaturation.

Temperature

  • Enzyme activity generally increases with temperature up to a point (optimal temperature).

  • Beyond this point, enzymes denature, diminishing catalytic ability.

Types of Denaturation

  • Reversible Denaturation: Activity returns when optimal conditions restored (e.g., slight temperature shifts).

  • Irreversible Denaturation: Permanent loss of function (e.g., cooking an egg).

Substrate Concentration Impact

  • Low substrate concentration = low reaction rate.

  • Increased concentration raises collision rate until saturation point is reached, where all active sites are occupied.

Inhibition Types

Competitive Inhibition

  • An inhibitor competes with the substrate for the active site, reducing reaction rate.

Non-Competitive Inhibition

  • An inhibitor binds allosterically, altering active site structure and hindering substrate binding.

Topic 3.4: Cellular Energy

Metabolic Pathways

  • Linked series of enzyme-catalyzed reactions (e.g., glycolysis, Krebs cycle).

  • Can be linear or cyclical (e.g., Krebs, Calvin cycle).

Autotrophs vs. Heterotrophs

  • Autotrophs: Produce own food (e.g., plants).

    • Photoautotrophs: Use light (e.g., plants, cyanobacteria).

    • Chemoautotrophs: Use inorganic substances for energy (e.g., certain bacteria).

  • Heterotrophs: Obtain energy from consuming other organisms (e.g., animals, decomposers).

Exergonic vs. Endergonic Reactions

  • Exergonic: Release energy (e.g., cellular respiration); increases entropy.

  • Endergonic: Require energy input (e.g., photosynthesis); decreases entropy.

ATP Structure and Function

  • ATP composed of ribose, adenine, and three phosphate groups.

  • ATP powers cellular work through energy release when breaking a phosphate bond to form ADP.

  • Energy Coupling: Linking exergonic reactions with endergonic reactions that require energy input (e.g., ATP formation).

Photosynthesis: The Big Picture

Photosynthesis Overview

  • Converts CO2 and water into glucose using light energy; oxygen is a byproduct.

    • Equation: 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2.

  • Endergonic process (requires energy input).

Evolution and Impact

  • Photosynthesis evolved ~3.5 billion years ago; crucial for creating oxygen-rich atmosphere and ozone layer.

Light Reactions

  • Occur in thylakoids: convert light energy into ATP and NADPH.

  • Inputs: light and water; outputs: ATP, NADPH, and oxygen.

  • Chlorophyll absorbs light, reflecting green light, leading to the production of ATP and NADPH.

Calvin Cycle

  • Uses ATP and NADPH to convert CO2 into glucose (G3P).

  • Three phases: carbon fixation, energy investment, and regeneration of RuBP.

Cellular Respiration: The Big Picture

Overview and Chemical Equation

  • Reaction: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP).

  • An exergonic reaction releasing energy and creating disorder.

  • Occurs in cell cytoplasm and mitochondria through multiple phases: glycolysis, link reaction, Krebs cycle, and electron transport chain.

Glycolysis

  • Takes place in cytoplasm; anaerobic process.

  • Phases: investment (ATP used), cleavage (forming G3P), and energy harvest (ATP and NADH produced).

  • Gross yield: 4 ATP (net yield: 2 ATP) and 2 NADH produced.

Link Reaction

  • Converts pyruvate into acetyl CoA; releases CO2 and generates NADH.

Krebs Cycle

  • Occurs in mitochondrial matrix; produces ATP, NADH, and FADH2 while releasing CO2.

Electron Transport Chain

  • Utilizes NADH and FADH2 to create ATP through chemiosmosis and proton gradient.

  • Oxygen acts as final electron acceptor.

Anaerobic Respiration and Fermentation

Differences Between Aerobic and Anaerobic Respiration

  • Aerobic Respiration: Requires oxygen; efficient (produces ~32 ATP).

  • Anaerobic Respiration: Lacks oxygen; only glycolysis and fermentation (produces 2 ATP).

Fermentation Types

  • Alcohol Fermentation: Occurs in yeast; converts pyruvate into ethanol and releases CO2.

  • Lactic Acid Fermentation: Occurs in muscle cells under low oxygen; converts pyruvate into lactic acid, regenerating NAD+.