Chapter 7: Cellular Respiration

Cellular Respiration Overview

• All life generates ATP by harvesting electrons from glucose.

• Two main parts: 1) Energy extracted from glucose into electron carriers (NADH, FADH2), releasing CO2; 2) Electrons used in electron transport chain for ATP synthesis, with O2 acting as the final electron acceptor, forming H2O.

Redox Reactions

• Many cellular respiration reactions involve electron transfer.

• Oxidation: Atom/molecule loses electrons.

• Reduction: Atom/molecule gains electrons.

• OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Stages of Cellular Respiration

Glycolysis

• Location: Cytoplasm.

• Process: Glucose (6 carbons) split into two pyruvate (3 carbons each).

• Products: Some NADH and ATP (via substrate-level phosphorylation).

Pyruvate Oxidation

• Location: Between glycolysis and Krebs cycle.

• Process: Pyruvate oxidized; one carbon removed as CO_2; NADH formed.

• Product: Remaining 2-carbon fragment becomes acetyl-CoA.

Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondrial matrix.

• Process: Acetyl-CoA combines with a 4-carbon molecule, forming a 6-carbon molecule. Series of redox reactions extracts energy.

• Products: NADH, FADH2, and ATP; remaining two carbons released as CO2.

Electron Transport Chain (ETC) & Chemiosmosis

• Location: Inner mitochondrial membrane.

• Process: NADH and FADH_2 transfer electrons to integral membrane proteins.

• ETC Function: Proteins pump protons (H^+) into the intermembrane space, creating a concentration gradient.

• Final Electron Acceptor: O2 accepts electrons and protons to form H2O.

• Chemiosmosis: Protons diffuse back into the mitochondrial matrix through ATP synthase channels, powering ATP synthesis from ADP (oxidative phosphorylation).

Overall Yield (from one glucose molecule)

• 6 CO_2 molecules released.

• 4 ATP molecules (net).

• 10 NADH electron carriers.

• 2 FADH_2 electron carriers.

Cellular Respiration Without Oxygen (Fermentation)

• Occurs when O_2 is absent.

• Glycolysis proceeds, producing pyruvate and NADH.

• Pyruvate (or another molecule) is used to oxidize NADH back to NAD^+ to continue glycolysis.

• Lactic Acid Fermentation: Pyruvate converted to lactate (e.g., human muscle cells for short periods).

• Ethanol Fermentation: Pyruvate converted to acetaldehyde (releasing CO_2), then reduced to ethanol (e.g., yeast).

Energy from Other Food Molecules

• Fats: Broken into fatty acids, converted to acetyl-CoA via \beta -oxidation, enters Krebs cycle.

• Proteins: Broken into amino acids, undergo deamination, converted into molecules that enter the Krebs cycle. Less efficient due to energy cost and toxic byproducts (NH_3).