7.4 Cellular Respiration and Photosynthesis

Cellular respiration is the powerhouse of energy production in cells. It breaks down glucose through a series of stages, each contributing to ATP generation. From glycolysis to oxidative phosphorylation, this process fuels cellular activities.

Energy flows through respiration like a well-orchestrated dance. Glucose is split, oxidized, and its energy harvested through electron transport. The result? A whopping 38 ATP molecules per glucose, powering life's essential functions.

Cellular Respiration

Stages of cellular respiration

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• Glycolysis breaks glucose into pyruvate in cytoplasm, net gain 2 ATP and 2 NADH
• Pyruvate oxidation converts pyruvate to acetyl-CoA in mitochondrial matrix, produces NADH
• Krebs cycle oxidizes acetyl-CoA to CO2 in mitochondrial matrix, yields 2 ATP, 6 NADH, 2 FADH2 per glucose
• Oxidative phosphorylation generates ATP through electron transport chain and chemiosmosis in inner mitochondrial membrane, produces up to 34 ATP per glucose

Energy flow in respiration processes

• Glycolysis splits 6-carbon glucose into two 3-carbon pyruvate molecules, net energy gain 2 ATP and 2 NADH
• Krebs cycle completely oxidizes acetyl-CoA (2C) to CO2, generates 2 ATP, 6 NADH, 2 FADH2 per glucose
• Oxidative phosphorylation harvests energy from NADH and FADH2, electrons flow through ETC
• Proton gradient drives ATP synthase, producing bulk of ATP (~34 molecules per glucose)

Light reactions vs dark reactions

• Light-dependent reactions occur in thylakoid membranes, require light energy

1. Split water molecules (photolysis)
2. Excite electrons in chlorophyll
3. Drive electron flow through photosystems I and II
4. Produce ATP and NADPH

• Light-independent reactions (Calvin cycle) happen in stroma, don't directly need light

1. Use ATP and NADPH from light reactions
2. Fix CO2 into glucose using RuBisCO enzyme
3. Regenerate carbon acceptor molecule (RuBP)

Redox reactions in energy conversion

• Cellular respiration oxidizes glucose, releases energy
• NAD+ and FAD act as electron acceptors, reduced to NADH and FADH2
• Electron transport chain uses redox reactions to pump protons, create gradient
• Photosynthesis uses light energy to drive electron excitation in chlorophyll
• Electrons flow through photosystems and ETC, reducing NADP+ to NADPH
• Water oxidized to provide electrons and protons, releases O2 as byproduct