Cellular Respiration Chapter 7

An overview of cellular respiration Figure 6.8 High-energy electrons carried by NADH GLYCOLYSIS GlucosePyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion Cytoplasmic fluid

Details of glycolysis in the cytoplasm Figure 6.9B Steps – A fuel molecule is energized, using ATP Glucose PREPARATORY PHASE (energy investment) Step Glucose-6-phosphate Fructose-6-phosphate Glyceraldehyde-3-phosphate (G3P) Step A six-carbon intermediate splits into two three-carbon intermediates. 4 Step A redox reaction generates NADH. 5 5 ENERGY PAYOFF PHASE 1,3-Diphosphoglyceric acid (2 molecules) 6 Steps – ATP and pyruvic acid are produced Phosphoglyceric acid (2 molecules) 7 2-Phosphoglyceric acid (2 molecules) 8 9 (2 molecules per glucose molecule) Pyruvic acid Fructose-1,6-diphosphate

What happens if oxygen is not present? Fermentation –Occurs in the cytosol –Generate NAD+ for recycling to glycolysis –No ATP production –Lactic acid and alcoholic fermentation

Lactic acid fermentation and alcoholic fermentation

Efficiency of glycolysis and fermentation

In the matrix of the mitochondria, each pyruvic acid molecule is broken down to form CO 2 and a two-carbon acetyl group, which enters the Krebs cycle When Oxygen is present : Pyruvic acid is chemically groomed for the Krebs cycle which takes place in the mitochondria Figure 6.10 Pyruvic acid CO 2 Acetyl CoA (acetyl coenzyme A)

The Krebs cycle, in the matrix of the mitochondria, is a series of reactions in which enzymes strip away electrons and H + from each acetyl group When Oxygen is present: The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH 2 molecules Figure 6.11A Acetyl CoA KREBS CYCLE 2 CO 2

Figure 6.11B Oxaloacetic acid Step Acetyl CoA stokes the furnace 1 2 carbons enter cycle Citric acid Steps and NADH, ATP, and CO 2 are generated during redox reactions. 23 CO 2 leaves cycle Alpha-ketoglutaric acid CO 2 leaves cycle Succinic acid KREBS CYCLE Steps and Redox reactions generate FADH 2 and NADH. 45 Malic acid

The electrons from NADH and FADH 2 travel down the electron transport chain to oxygen Energy released by the electrons is used to pump H + into the space between the mitochondrial membranes In chemiosmosis, the H + ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP Chemiosmosis powers most ATP production in the inner membrane

Chemiosmosis in the mitochondrion inner membrane Figure 6.12 Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron carrier Electron flow ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Connection: Certain poisons interrupt critical events in cellular respiration Figure 6.13 Rotenone Cyanide, carbon monoxide Oligomycin ELECTRON TRANSPORT CHAIN ATP SYNTHASE

For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Review: Each molecule of glucose yields many molecules of ATP KREBS CYCLE Electron shuttle across membranes Cytoplasmic fluid GLYCOLYSIS Glucose 2 Pyruvic acid 2 Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Mitochondrion by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation Maximum per glucose: Figure 6.14

Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP –But a cell must have a way of replenishing NAD+ Fermentation is an anaerobic alternative to aerobic respiration