Topic 5: Energy for Biological Processes

Aerobic Respiration

• Conversion of glucose into energy with oxygen, resulting in CO2 and water.
• Anaerobic respiration occurs without oxygen, producing lactic acid.
• Respiration involves multiple steps, each catalyzed by specific enzymes.
• Both types yield ATP for metabolic reactions and heat generation.
• Key Stages:
  • Glycolysis
  • Link Reaction
  • Krebs Cycle
  • Oxidative Phosphorylation

Glycolysis

• First step of both aerobic and anaerobic respiration.
• Occurs in cytoplasm.
• Converts glucose to:
  • 2 pyruvate molecules
  • 2 ATP molecules
  • 2 NADH molecules
• In anaerobic conditions, pyruvate becomes lactate, affecting blood pH and CNS.

Link Reaction and Krebs Cycle

• Link Reaction: Pyruvate to acetyl CoA using NADH.
• Krebs Cycle: Acetyl CoA oxidation producing CO2, ATP, NADH, FADH2.
• Occurs in mitochondrial matrix.

Oxidative Phosphorylation

• ATP synthesis via chemiosmosis in mitochondria's electron transport chain.
• Majority of ATP in aerobic respiration generated here.
• Process involves:
  • NADH2 and FADH2 transporting H+ and electrons.
  • Series of redox reactions transferring electrons.
  • H+ ions move into intermembrane space then back, producing ATP.
  • Oxygen combines with H+ and electrons to form water.

Photosynthetic Pigments

• Photosynthesis splits water molecules using light energy to produce glucose and release O2.
• Influenced by CO2 concentration, light intensity, and temperature.
• Chloroplasts are the site:
  • Grana contain photosynthetic pigments (e.g., chlorophyll) arranged in photosystems.
  • Stroma contains enzymes for light-independent reactions.

Absorption and Action Spectrum

• Absorption Spectrum: Range of light wavelengths absorbed by pigments.
• Action Spectrum: Photosynthesis rate vs. wavelength absorbed.
• Multiple pigments (e.g., chlorophyll a/b, carotenoids) absorb various wavelengths, increasing efficiency.

Photosynthesis

Light-dependent Reaction

• Electrons in chlorophyll excited to higher energy levels.
• Electron Transport Chain generates ATP and reduced NADP.
• Cyclic vs. Non-Cyclic Phosphorylation:
  • Cyclic: Electrons return to Photosystem I.
  • Non-Cyclic: Electrons cycle from Photosystem II to I, involving photolysis of water.

Light-independent Reaction (Calvin Cycle)

• Uses ATP/NADP to produce glucose.
• Steps:
  1. Carbon fixation: RuBP + CO2 catalyzed by RUBISCO.
  2. Conversion to glycerate 3-phosphate (GP).
  3. GP to GALP using ATP and NADP.
  4. GALP makes glucose and other compounds.
  5. Reforming RuBP with ATP.