University:
University of North Georgia
Course:
BIOL 3240K | Cell Biology
Academic year:

2022
Views:

50

Pages:

15
Author:

do3ran7ut

Figure 9.13 The Respiratory Chain and ATP Synthase Produce ATP by a Chemiosmotic Mechanism Concept 9.3 Oxidative Phosphorylation Forms ATP ATP synthase can also act as ATPase, hydrolyzing ATP to ADP and Pi. Why is ATP synthesis favored? • ATP leaves the matrix as soon as it is made, keeping ATP concentration in the matrix low. • H+ gradient is maintained by active transport. (7) Concept 9.3 Oxidative Phosphorylation Forms ATP The first experimental evidence of chemiosmosis came from studies on isolated chloroplast thylakoid membranes. (8) Concept 9.3 Oxidative Phosphorylation Forms ATP In brown fat cells, a protein called UPC1 inserts into the mitochondrial membrane and makes it permeable to protons. This uncouples electron transport and chemiosmosis, and energy is released as heat rather than being trapped in ATP. (9) Concept 9.3 Oxidative Phosphorylation Forms ATP ATP synthase is the same in all living organisms. It is a molecular motor with two parts: • F0 unit—a transmembrane H+ channel • F1 unit—projects into the matrix; rotates to expose active sites for ATP synthesis (11) Figure 9.15 How ATP Is Made Concept 9.3 Oxidative Phosphorylation Forms ATP When H+ diffuses through the channel, the potential energy is converted to kinetic energy, causing the central polypeptide to rotate. The energy is transmitted to the catalytic subunits of F1, resulting in ATP synthesis. (12) Concept 9.3 Oxidative Phosphorylation Forms ATP Many bacteria and archaea use alternate electron acceptors such as SO4-2, Fe3+, and CO2 (anaerobic respiration). This allows them to exist where O2 is scarce or absent. (13) Concept 9.4 In the Absence of Oxygen, Some Energy Is Harvested from Glucose Without O2, some ATP can be made by glycolysis and fermentation. • Occurs in the cytoplasm • Glucose is only partially oxidized • 2 ATP per glucose are produced by substrate-level phosphorylation • In all types, NAD+ is regenerated to keep glycolysis going (1) Concept 9.4 In the Absence of Oxygen, Some Energy Is Harvested from Glucose Lactic acid fermentation • Pyruvate is the electron acceptor; lactate is the product. • Microorganisms and some complex organisms. • Lactate dehydrogenase catalyzes fermentation; in presence of O2, it catalyzes oxidation of lactate to pyruvate. (2) Figure 9.16 Fermentation (Part 1) Concept 9.4 In the Absence of Oxygen, Some Energy Is Harvested from Glucose In large vertebrate muscle cells during intense exercise, O2 cannot be delivered fast enough for aerobic respiration. Muscle cells then break down glycogen and carry out lactic acid fermentation. When lactate builds up, the increase in H+ lowers pH and causes muscle pain. (3) Concept 9.4 In the Absence of Oxygen, Some Energy Is Harvested from Glucose Alcoholic fermentation • Yeasts and some plant cells • Requires two enzymes to metabolize pyruvate to ethanol • Reactions are reversible • Used to produce alcoholic beverages (4) Concept 9.4 In the Absence of Oxygen, Some Energy Is Harvested from Glucose (5) Cellular respiration yields more energy than fermentation. • Glycolysis plus fermentation = 2 ATP • Glycolysis plus cellular respiration = 32 ATP Glucose is only partially oxidized in fermentation, more energy remains in the products than in CO2. Figure 9.17 Cellular Respiration Yields More Energy Than Fermentation