Chapter 7 – The Working Cell: Energy from Food College Prep Biology Mr. Martino

7.1 How Cells Make ATP Cellular Respiration: harvesting of E from food molecules by cells 2 types of respiration: Aerobic: requires oxygen (harvests 40% of E in glucose) Anaerobic: does not require oxygen (harvests 2% of E in glucose) Evolved about 3.8 billion years ago - before oxygen C6H12O6 + 6 O2 6 CO2 + 6 H2O + E Glucose is the example carbohydrate

Glycolysis: (exergonic) splits glucose into 2 pyruvic acid Occurs in cytoplasm Oxygen is final electron acceptor = water Enzymes catalyze First stage of all respiration

Overview of Aerobic Respiration Aerobic Respiration is continuous – but occurs in 3 main stages Glycolysis: (exergonic) splits glucose into pyruvic acid Occurs in cytoplasm Kreb’s Cycle: (exergonic) completes glucose breakdown - pyruvic acid becomes CO2 ETC: (endergonic) NADH and FADH2 shuttle e- and generates most of cell’s ATP by chemiosmosis

Two Mechanisms Generate ATP Chemiosmosis: cells use the potential E of concentration gradients to make ATP Depends upon membranes and ATP synthase ETC makes this E transport possible Cells generate most of their E this way

Substrate-level phosphorylation: an enzyme transfers a P-group from a substrate to ADP No membrane involved Only generates a small percentage of a cell’s ATP

7.3 Second Stage – Pyruvic Acid Conversion and Kreb’s Cycle 2 pyruvate molecules from glycolysis enter mitochondrion Pyruvic acid from glycolysis does not enter the Kreb’s cycle 1. It is oxidized while NAD+ is reduced to NADH 2. 1 C is released in the form of CO2 3. Coenzyme A + fragment = acetyl CoA Each glucose produces 2 acetyl CoAs for Kreb’s

Kreb’s Cycle Only the acetyl part of acetyl CoA participates Each turn of Kreb’s produces: 1 ATP by substrate level phosphorylation 3 NADH 1 FADH2 Turns twice per glucose

7.4 Third Stage – Electron Transport System Final stage of respiration is ETC & ATP formation The fold of the cristae provide space for many ETC’s and ATP synthases NADH is shuttled down the e- carriers Oxygen is the final e- (H) acceptor forming H2O Proteins shuttle H+ across the membrane The greater the gradient the more potential E H+ are passed through ATP synthase which catalyzes the formation of about 34 ATP

7.5 Anaerobic Respiration 2 forms of anaerobic respiration Alcoholic fermentation: anaerobic respiration in which pyruvic acids form ethyl alcohol Performed by yeasts and bacteria Releases CO2 Ethanol is toxic to the organisms who produce it – if too concentrated

7.5 – con’t Lactic Acid Fermentation: anaerobic fermentation in which pyruvic acids form lactic acids Used to make cheese and yogurt Occurs in muscle cells – causing pain and fatigue No CO2 is released