Energy transfers official content revision notes

Energy Transfers in Biological Systems

Photosynthesis

Light-Dependent Reactions

• Chlorophyll Photoionisation: When chlorophyll absorbs light energy, it becomes excited and loses electrons, initiating the light-dependent reactions.
• Electron Transfer: The lost electrons are transferred through a series of proteins in the thylakoid membrane, known as the electron transport chain.
• ATP Production: As electrons move through the chain, energy is released and used to pump protons into the thylakoid lumen, creating a proton gradient that drives ATP synthase to produce ATP.
• Reduced NADP: Electrons ultimately reduce NADP+ to form NADPH, which is used in the Calvin cycle.
• Photolysis: Water molecules are split to replace lost electrons, producing oxygen as a byproduct.

Calvin Cycle

• RuBP and GP: Carbon dioxide is fixed by ribulose bisphosphate (RuBP) to form glycerate-3-phosphate (GP).
• Triose Phosphate: GP is then converted into triose phosphate using ATP and NADPH.
• Rubisco: The enzyme ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the fixation of CO2.

Respiration

Glycolysis, Link Reaction, and Krebs Cycle

• Glycolysis: Glucose is broken down into pyruvate, producing a small yield of ATP and NADH.
• Link Reaction: Pyruvate is converted into acetyl CoA, releasing CO2 and generating NADH.
• Krebs Cycle: Acetyl CoA enters the Krebs cycle, producing ATP, NADH, FADH2, and CO2.

Oxidative Phosphorylation

• Electron Transfer and Proton Gradients: NADH and FADH2 donate electrons to the electron transport chain, creating a proton gradient across the inner mitochondrial membrane.
• ATP Synthase: Protons flow back through ATP synthase, driving the production of ATP.

Anaerobic vs Aerobic Respiration

• Aerobic Respiration: Occurs in the presence of oxygen, yielding a high amount of ATP.
• Anaerobic Respiration: Occurs without oxygen, resulting in less ATP and producing byproducts like lactic acid in mammals or ethanol in yeast.