Higher Human Biology Unit 1 Human Cells KEY

Higher Human Biology Unit 1 Human Cells KEY AREA 7: Cellular Respiration

Human Cells Learning Intentions KEY AREA 7 – Cellular Respiration 1. Role of ATP 2. Metabolic Pathways of Cellular Respiration 3. Regulation of Cellular Respiration Pathways

7 a) Role of ATP Cellular respiration is a series of metabolic pathways that releases energy from food and generates a high energy compound called adenosine triphosphate (ATP) ATP is composed of adenosine and three inorganic phosphate (Pi) groups Energy is released from ATP when the bond attached to the terminal phosphate is broken by enzyme action ATP releases energy and breaks down to form Adenosine diphosphate (ADP) and inorganic phosphate (Pi) ADP + Pi ATP (this reaction is called Phosphorylation)

7 b) Role of ATP is very important as it acts as the link between catabolic energy releasing reactions (e. g. respiration) and anabolic energy-consuming reactions (e. g. protein synthesis) There is a rapid turnover of ATP in a cell ATP is continuously made at the same time as it is being used up, so there is no need for humans to have a vast store of ATP Phosphorylation is an enzyme controlled process by which a phosphate group is added to a molecule Phosphorylation also occurs when the phosphate and energy are transferred from ATP to the molecules of a reactant in a metabolic pathway, making them more reactive

7 c) Metabolic Pathways of Cellular Respiration Cellular respiration is a series of metabolic pathways that releases energy from food and generates a high energy compound called adenosine triphosphate (ATP) There are 3 stages involved in Cellular Respiration: Stage 1 – Glycolysis (occurs in the cytoplasm of a cell) Stage 2 – Citric Acid Cycle (occurs in the central matrix of mitochondria) Stage 3 – Electron Transport Chain (occurs in the inner membrane of mitochondria)

7 d) Glycolysis is the breakdown of glucose to pyruvate under the control of enzymes 1. Energy investment phase • 2 ATP are required for the phosphorylation of glucose and intermediates 2. Energy payoff phase • 4 ATP are produced during the breakdown of the final intermediate into pyruvate 3. Net gain of 2 ATP per molecule of glucose 4. Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH 5. No oxygen is required for Glycolysis

7 e) Glycolysis

7 f) Citric Acid Cycle 2 nd Stage of Respiration a) Formation of Citrate 1. This stage only occurs in aerobic conditions (aerobic respiration) 2. Pyruvate is broken down to an Acetyl Group that combines with Coenzyme A (Acetyl Coenzyme A) 3. Acetyl Coenzyme A + Oxaloacetate Citrate b) The Citric Acid Cycle 4. Citric Acid Cycle involves many enzyme controlled steps which results in: - Release of Carbon Dioxide - Generation of ATP - Dehydrogenase enzymes remove H+ ions and electrons and pass them to NAD to make NADH - Regeneration of Oxaloacetate

7 g) Citric Acid Cycle

7 h) Electron Transport Chain 1. The hydrogen ions and electrons from NADH are passed to the electron transport chain 2. The electron transport chain consists of a series of carrier proteins attached to the inner membrane of the mitochondria ATP synthesis 3. Electrons are passed along the electron transport chain releasing energy 4. This energy is used to pump hydrogen ions across the inner mitochondrial membrane 5. These ions then flow back through the membrane protein ATP synthase synthesising ATP 6. Oxygen combines with hydrogen ions and electrons to form water

7 i) Electron Transport Chain

Human Cells Questions KEY AREA 7 – Cellular Respiration 1. Testing Your Knowledge 1 Page 106 2. Quick Quiz Q’s 1 -3