AP Biology Unit 3: Cellular Energetics Lecture Notes

Introduction

• Unit 3 covers Cellular Energetics in AP Biology.
• Topics include: Enzymes, Cellular Energy, ATP, Photosynthesis, and Cellular Respiration.
• The lecture aims to prepare students for unit exams and the AP Biology test.

Enzymes (Topics 3.1 to 3.3)

Key Properties

• Enzymes are usually proteins; some RNAs act as enzymes.
• Catalyze reactions by lowering activation energy.
• Highly specific due to complementary shapes and charges with their substrates.

Structure and Function

• Enzymes have secondary, tertiary, and quaternary structures involving hydrogen bonds, ionic bonds, and hydrophobic clustering.
• Environmental changes (pH, temperature, ion concentration) can denature enzymes, altering their shape and function.

pH and Temperature Effects

• Enzyme activity peaks at a pH optimum; deviation causes denaturation and reduced function.
• Enzyme activity increases with temperature to a point, beyond which denaturation occurs.

Substrate Concentration

• Low substrate concentration results in low reaction rates; increasing concentration increases the rate until saturation.

Inhibition

• Competitive Inhibition: Foreign molecule blocks active site.
• Non-Competitive Inhibition: Molecule binds to an allosteric site, altering active site shape.

Cellular Energy (Topic 3.4)

Metabolic Pathways

• Linked enzymatic reactions within a cell (e.g., glycolysis, Krebs cycle, Calvin cycle).
• Can be linear or cyclical.

Autotrophs vs. Heterotrophs

• Autotrophs: Produce own food (e.g., plants).
  • Photoautotrophs: Use light energy.
  • Chemoautotrophs: Use inorganic substances.
• Heterotrophs: Obtain energy by consuming organic compounds.

Exergonic vs. Endergonic Reactions

• Exergonic: Release energy; increase entropy.
• Endergonic: Require energy; decrease entropy.

ATP

• Structure: Ribose sugar, adenine base, three phosphates.
• Function: Energy storage and release through phosphorylation.

Photosynthesis

Overview

• Converts light energy into chemical energy (glucose).
• Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (endergonic reaction).

Evolutionary Impact

• Photosynthesis evolved 3.5 billion years ago.
• Led to oxygen-rich atmosphere and ozone layer.

Light Reactions

• Occur in thylakoid membranes; produce ATP and NADPH.
• Key structures: Photosystems, electron transport chains, ATP synthase.

Calvin Cycle

• Converts ATP and NADPH into carbohydrates.
• Phases: Carbon Fixation, Reduction, Regeneration.

Cellular Respiration

Overview

• Converts glucose into ATP; involves glycolysis, Krebs cycle, and oxidative phosphorylation.
• Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (exergonic reaction).

Glycolysis

• Occurs in the cytoplasm; anaerobic.
• Phases: Investment, Cleavage, Energy Harvest.

Link Reaction and Krebs Cycle

• Pyruvate converted to acetyl-CoA; occurs in mitochondrial matrix.
• Krebs Cycle generates NADH, FADH₂, and ATP.

Electron Transport Chain

• Occurs in mitochondrial inner membrane; generates most ATP through chemiosmosis.

Fermentation

• Anaerobic process; regenerates NAD+ to maintain glycolysis.
• Types: Alcohol and Lactic Acid Fermentation.

Comparing Photosynthesis and Cellular Respiration

• Both involve electron transport chains and ATP generation via chemiosmosis.
• Evolutionary links suggest common ancestry of chloroplasts and mitochondria.

Conclusion

• Unit 3 is challenging but understanding these concepts is crucial for success in AP Biology.
• Resources like quizzes, flashcards, and interactive tutorials are available to reinforce learning.