Higher Human Biology Human Cells Cellular Respiration 1

What do you know? �In Pairs �From N 5 Brain Storm what you know of respiration and put it on the sheets of A 2 paper. �Review with class 2

What are you going to learn? �More detail about the 3 different stages of cellular respiration including the names of the enzymes involved. �More detail about how ATP is synthesised. �About some alternative substrates for respiration. �About the regulation of the chemical pathways involved with respiration. 3

Introduction and ATP �Why is respirations so important to cells? �It regenerates ATP from ADP and Pi �How do they do that? �They take ‘food’ i. e. glucose and through a series of metabolic pathways release energy which used to regenerate ATP �What do cells use the energy rich ATP for? �Building proteins, cellular respiration etc. …. 4

ATP �Glucose is broken down, releasing hydrogen ions and electrons by dehydrogenase enzymes. �The electrons provide the energy to regenerate ATP from ADP + Pi. requires energy low energy ADP + Pi ATP high energy state releases energy state �The metabolic pathways for cell respiration are linked to many other pathways because they produce the energy needed for them as ATP. �ATP = adenosine triphosphate 5

ATP �ATP is the molecule that transfers energy between catabolic and anabolic metabolic pathways in cells. carbon dioxide and water (catabolic) glucose and oxygen ATP amino acids (anabolic) ADP + Pi protein �ATP is able to release energy by removing a Pi molecule. 6

ATP �ATP makes phosphate available to phosphorylate other molecules in a process called phosphorylation. �Phosphorylation is where a phosphate group is added to another molecule. HOW MUCH ATP? �ATP is continuously being used and regenerated. �This may occur at a rate equivalent to 400 g/h. �The store of ATP in the body is thought to remain at approximately 50 g at any one time. 7

What type of reactions need energy? 8

What do you know now? �What is the purpose of cellular respiration? �What is the primary substrate for respiration? �What is released from the substrate? �What are the enzymes called that do this? �What is regenerated in respiration? �What is phosphorylation? �What are catabolic reactions? �What are anabolic reactions? �Name examples of these reactions 9

Mitochondria 10

Cellular respiration �The three stages of cellular respiration are called �Glycolysis �Citric acid cycle �Electron transport chain TRIOS Sit in groups of 3 and number yourselves 1, 2, 3 1 s are glycolysis and sit table 1 2 s are citric acid cycle and sit at table 2 3 s electron transport system and sit at table 3 On A 2 paper summarise your section, use diagrams etc. Come back together and share your section, 1 then 2 then 3 11

Glycolysis �In cytoplasm �Splitting of glucose to form pyruvates �A series of enzyme controlled steps � 2 ATP used in energy investment phase � 4 ATP generated in energy pay off stage �Net gain of 2 ATP �Some H+ ions released by dehydrogenase in energy pay off stage carried by coenzyme molecule NAD to give NADH 12

Glycolysis 13

Phosphorylation in glycolysis �Occurs twice in glycolysis. �First phosphorylation occurs when phosphate is added to glucose producing an intermediate compound that can go into a number of metabolic pathways. �Second phosphorylation occurs with enzyme phosphofructokinase adds another phosphate. This is irreversible and leads to the production of pyruvate in the glycolytic pathway. �Pyruvate will progress into the citric acid cycle if oxygen is present. �Fermentation will occur if no oxygen is present. 14

Citric Acid Cycle �Occurs in the matrix of the mitochondria. �Pyruvate is broken down to an acetyl group. �Each acetyl group combines with Coenzyme A to give Acetylcoenzyme A. �Acetylcoenzyme A combines with oxaloacetate to produce citrate �Citrate goes through a series of enzyme mediated reactions to produce oxaloacetate. This produces CO 2, NADH, FADH 2 and ATP �Dehydrogenase enzyme removes hydrogen ions and high energy electrons which are passed to coenzymes NAD or FAD to produce NADH and FADH 2. �Both are used later in the electron transport chain. 15

Citric Acid Cycle 16

Electron Transport Chain �On inner membrane of the mitochondria. �Produces most of the ATP fro aerobic respiration. �High energy electrons are used to pump hydrogen ions across the inner membrane. �The flow of ions allows ATP synthase to rotate and catalyse the regeneration of ADP and Pi into ATP. �The final electron receptor is oxygen. �Oxygen combines with the hydrogen ions to produce water. �This produces 36 molecules of ATP 17

Electron transport chain 18

Substrates for Respiration �Glucose is the usual respiratory substrate used by cells from either the breakdown of starch or glycogen. �Other sugars can be used as these can produce glucose or other intermediates. �Proteins form amino acids when broken down. Deamination in the liver produces molecules that can be used either in glycolysis or the citric acid cycle as respiratory substrates. �Fats can be broken down to glycerol and fatty acids. These can be used as intermediates in glycolysis and the citric acid cycle respectively. 19

Glucose as the respiratory substrate starch maltose glycogen glucose sucrose fructose pyruvate 20

Protein as a respiratory substrate glucose protein Amino acids e. g. alanine pyruvate Amino acids e. g. leucine Acetyl coenzyme A Amino acids e. g. aspartic acid intermediate Citric acid cycle 21

Fat as a respiratory substrate glucose glycerol fat intermediate pyruvate fatty acids acetyl coenzyme A Citric acid cycle 22

Regulation of cellular respiration by feedback inhibition �Like many biochemical pathways cellular respiration is regulated by feedback inhibition �If ATP is not being used then the high concentration will inhibit the activity of phosphofructokinase which will slow down glycolysis. �If ATP concentration decreases the enzyme will no longer be inhibited and glycolysis will speed up. 23

Regulation of cellular respiration by feedback inhibition �A high concentration of citrate will inhibit phosphofructokinase but if the citrate concentration falls the enzyme will not be inhibited. Glycolysis will speed up supplying more acetyl groups for the citric acid cycle. �This feedback inhibition has the advantages of conserving resources, producing ATP when needed and not building up too many intermediate compounds. �So the inhibition of the phosphofructokinase synchronises the rates of glycolysis and citric acid cycle 24

What do I need to know? Glycolysis �Where does this stage occur? �What is glucose broken down to? �What is meant by the energy investment phase? �What occurs during step 1? �Where does the second phosphorylation occur? �What is the name of the enzyme that catalyses the second phosphorylation? �Is the second phosphorylation reversible/irreversible? �What occurs in the energy payoff phase? �What happens to the pyruvate produced? �How many ATP are produced during this phase? 25

What do I need to know? Citric acid cycle �Where does this stage occur? �What happens to the pyruvate? �What does the acetyl co. A combine with and what odes it produce? �A series of intermediates are produced, what controls theses reactions? �Why is carbon dioxide produce at this stage? �Why is it important that oxaloacetate is continually produced? �What are the names of the two coenzymes involved? �What do these coenzymes do? �What enzymes remove the hydrogens? �What else is generated at this stage? 26

What do I need to know? Electron transport chain �Where does this stage occur? �What is the electron transport chain? �What do NADH and FADH 2 do here? �What are the electrons used for? �What is the fate of the H+ ions? �What does the return flow of H+ ions cause to happen? �How is ATP synthesised? �What is the final electron acceptor? �What does the final electron acceptor combine with and what does this produce? �How many ATP molecules are generated in the Aerobic phase of respiration? 27

What do I need to know? Substrates �What are the possible substrates for respiration? �For each of the possible substrates state the following: �What must happen to them first? �Where in the cycle they enter? �In what circumstances are these substrates uesd? 28

What do I need to know? Regulation �Why does the production of ATP need to be regulated? �When would the supply of ATP increases/decrease? �What happens if the cell produces too much ATP? �Describe the mechanism of inhibition of the enzyme phosphofructokinase by citrate �How does the inhibition of phosphofructokinase by citrate synchronise the rate of both glycolysis and the citric acid cycle? 29