AP Biology Unit 3: Cellular Energetics

Introduction

• AP Biology Unit 3 covers challenging topics including cellular respiration and photosynthesis.
• Objective: Prepare students for the unit exam and AP Bio test.

Lecture Overview

• Enzymes
• Cellular Energy and ATP
• Photosynthesis
  • Big Picture
  • Light Reactions
  • Calvin Cycle
• Cellular Respiration
  • Big Picture
  • Glycolysis
  • Link Reaction
  • Kreb Cycle
  • Electron Transport Chain

Enzymes

Key Properties

• Enzymes are usually proteins; some RNAs can act like enzymes.
• Function by lowering activation energy, increasing reaction rates.
• Highly specific due to active site shape and charge complementing the substrate.

Structure and Function

• Levels: Secondary, Tertiary, Quaternary structures with hydrogen, ionic bonds.
• Optimal Conditions: pH, ion concentration, temperature affect enzyme activity.
• Denaturation: Can be reversible or irreversible, affecting enzyme shape and function.

Factors Affecting Activity

• pH: Enzyme activity decreases as pH moves away from optimal level.
• Temperature: Activity rises with temperature up to a point, then decreases due to denaturation.
• Substrate Concentration: Activity increases with substrate until saturation point.

Inhibition

• Competitive: Inhibitor blocks active site.
• Non-Competitive: Inhibitor binds to allosteric site, altering enzyme shape.

Cellular Energy

Metabolic Pathways

• Series of enzyme-catalyzed reactions within a cell.
• Examples: Glycolysis, Kreb cycle, Calvin cycle.

Autotrophs

• Photoautotrophs: Use light energy (e.g., plants).
• Chemoautotrophs: Use inorganic chemical reactions.

ATP

• Structure: Ribose sugar, adenine base, three phosphates.
• Function: Powers cellular work.
• Energy Coupling: Links exergonic and endergonic reactions.

Photosynthesis

Overview

• Converts CO2 and H2O to glucose using light energy.
• Formula: 6CO2 + 6H2O → C6H12O6 + 6O2.
• Endergonic reaction.

Historical Context

• Evolved ~3.5 billion years ago.
• Consequences: Oxygen-rich atmosphere, aerobic metabolism, ozone layer.

Process Phases

• Light Reactions: Convert light to chemical energy (ATP, NADPH).
• Calvin Cycle: Converts ATP and NADPH to carbohydrates.

Chlorophyll

• Absorbs light energy; found in thylakoid membranes.
• Absorption Spectrum: Peaks in blue/red, low in green.

Chloroplast Structure

• Contains thylakoids, grana, stroma.
• Site of photosynthesis reactions.

Cellular Respiration

Overview

• Converts glucose to ATP, CO2, H2O.
• Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP.
• Exergonic reaction.

Phases

1. Glycolysis: Occurs in cytoplasm, anaerobic, produces ATP and pyruvate.
2. Link Reaction: Converts pyruvate to acetyl-CoA, releases CO2.
3. Kreb Cycle: Produces NADH, FADH2, ATP, CO2 in mitochondrial matrix.
4. Electron Transport Chain: Produces most ATP via oxidative phosphorylation.

Anaerobic Respiration

• Occurs without oxygen, involves glycolysis and fermentation.
• Alcohol Fermentation: Produces ethanol, CO2.
• Lactic Acid Fermentation: Occurs in muscles, produces lactate.

Conclusion

• Cellular energetics is a complex and essential topic in AP Biology.
• Success requires understanding of metabolic pathways, energy transformations, and enzyme functions.