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

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

7a) 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)

7b) Role of ATP 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

7c) 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)

7d) Glycolysis 1st Stage of Respiration Occurs in the cytoplasm of a cell Glucose  Pyruvate (enzyme controlled process) Energy investment phase (2 ATP are needed for Glycolysis) 1st Phosphorylation produces an intermediate which can continue to other metabolic pathways 2nd Phosphorylation is catalysed by phosphofructokinase and is an irreversible reaction which can only lead to Glycolysis pathway Energy payoff phase (4 ATP are produced) Net gain of 2 ATP per molecule of glucose Hydrogen ions are released from glucose by dehydrogenase enzyme H+ ions are passed onto NAD forming NADH No oxygen required for Glycolysis

7e) Glycolysis

7f) Citric Acid Cycle Citric Acid Cycle 2nd Stage of Respiration Occurs in the central matrix of mitochondia a) Formation of Citrate Oxygen is required (aerobic respiration) Pyruvate is broken down to an Acetyl Group that combines with Coenzyme A (Acetyl Coenzyme A) H+ ions are released and bind to NAD forming NADH Carbon Dioxide is released Acetyl Coenzyme A + Oxaloacetate  Citrate b) The Citric Acid Cycle Occurs in the central matrix of the mitochondria Citric Acid Cycle involves many enzyme controlled steps which results in:- - Regeneration of Oxaloacetate - Release of Carbon Dioxide - Generation of ATP Dehydrogenase enzymes remove H+ ions and high energy electrons and pass them to NAD to make NADH, and FAD to make FADH2

7g) Citric Acid Cycle

7h) Electron Transport Chain 3rd Stage of Respiration Occurs in the inner membrane of mitochondia The electron transport chain consists of protein molecules found attached to the inner membrane of the mitochondria NADH and FADH2 from Glycolysis and the Citric Acid pathways release high-energy electrons to the electron transport chain on the mitochondrial membrane and this results in the synthesis of the bulk of ATP ATP synthesis High energy electrons are used to pump hydrogen ions across a membrane and flow these ions back through the membrane synthesising ATP using the membrane protein ATP synthase Final electron acceptor is oxygen Oxygen combines with hydrogen ions and electrons to form water

7i) Electron Transport Chain

7j) Substrates for Respiration Fate Starch & Glycogen Broken down into Glucose and feed into the GlycolyticPathway Other Sugars (e.g. maltose, sucrose) – converted to glucose and feed into the Glycolytic Pathway Fats broken down into Fatty Acids & Glycerol. Glycerol feeds into the Glycolytic Pathway, and the Fatty Acids enter the pathway as Acetyl Coenzymes A for use in the Citric Acid Cycle Proteins Amino Acids are de-aminated forming intermediates that can enter the respiratory pathway as pyruvate, acetyl coA, or intermediates of the Citric Acid Cycle

7k) Regulation of Cellular Respiration Pathways The cell conserves its resources by only producing ATP when required As the rate of glycolysis and the citric acid cycle increases, ATP supply increases As the rate of glycolysis and the citric acid cycle decreases, ATP supply decreases If a cell produces more ATP than it needs, the high concentration of ATP inhibits phosphofructokinase, and slows down the rate of glycolysis When the concentration of ATP decreases, the enzyme is no longer inhibited and glycolysis speeds up The rate of glycolysis and the rate of the citric acid cycle are synchronised by the inhibition of phosphofructokinase by citrate If citrate accumulates, glycolysis slows down If citrate consumption increases, glycolysis increases the supply of acetyl groups to the citric acid cycle

7l) Regulation of Cellular Respiration Pathways

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