Key Area 1: Cellular respiration Glycolysis, Citric Acid Cycle, Electron Transport Chain Unit 2: Metabolism and Survival

Glycolysis CfE Higher Biology Metabolism and Survival In this series of reactions, the sugar _________ is broken down into __________. ________ control these reactions, which are called _____________. Glycolysis takes place in the __________ of the cell and _________ required oxygen.

Glycolysis CfE Higher Biology Metabolism and Survival This process requires the energy from 2 ATP molecules in order to start it. This is an energy investment as the ATP is used to phosphorylate intermediates in glycolysis. The series of reactions in glycolysis produces four ATP molecules resulting in a net gain of two ATP (energy payoff)

Glycolysis CfE Higher Biology Metabolism and Survival Glucose 6C Pyruvate 3C 2NAD 2NADH (reduced) 2 ATP 2 ADP + 2P i 4 ADP + 4 P i 4 ATP Energy investment phase Energy payoff phase To electron transport system if oxygen present Net gain of 2ATP molecules Anaerobic respiration if oxygen absent

Glycolysis CfE Higher Biology Metabolism and Survival Dehydrogenase enzymes have removed hydrogen ions and high energy electrons. These are passed to NAD or _______________________ which is a ____________, The reduced form of NAD is formed NADH. This NADH will be used to produce ATP later in respiration. Two NAD molecules are involved at this point producing two NADH

Glycolysis CfE Higher Biology Metabolism and Survival Where does glycolysis take place in the cell? What is net gain in ATP from one glucose molecules during glycolysis? Is glycolysis anabolic or catabolic? Why?

After glycolysis what's next? CfE Higher Biology Metabolism and Survival The pyruvate formed in glycolysis passes onto the CITRIC ACID CYCLE if Oxygen is present. Where does the Citric Acid Cycle occur?

Mitochondrion – the site of aerobic respiration CfE Higher Biology Metabolism and Survival Cristae – the site of electron transport chain Matrix – the site of the Citric Acid Cycle (Krebs Cycle)

2CO 2 Pyruvate Acetyl coenzyme A 3NAD FAD FADH 2 3NADH ADP + PiATP The Citric acid cycle NAD NADH 2CO 2 All the 2NADH 2 go to the electron transfer system Citrate Oxaloacetate Coenzyme A

CfE Higher Biology Metabolism and Survival CompoundNumber of carbons Pyruvate Acetyl coenzyme A Citrate Oxaloacetate CO 2

The Citric Acid Cycle 1.If oxygen is available pyruvate is broken down to carbon dioxide and an acetyl group. 2.Each acetyl group combines with coenzyme A to form acetyl coenzyme A. As this happens H ions are released and become joined to NAD forming NADH. 3.The acetyl group of acetyl coenzyme A combines with oxaloacetate to form citrate and enters the citric acid cycle. 4.After several enzyme-controlled steps oxaloacetate is regenerated. CfE Higher Biology Metabolism and Survival

The Citric Acid Cycle 5.During some of these steps dehydrogenase enzymes remove H ions along with associated high-energy electrons. These H ions and high- energy electrons are passed to the coenzyme NAD to form NADH. 6.Also a similar reaction occurs but the coenzyme is FAD which becomes FADH 2. 7.In addition, ATP is produced at one of the steps and carbon dioxide is released at two of the steps. This all occurs in the central matrix of the mitochondrion CfE Higher Biology Metabolism and Survival

Electron Transport Chain An electron transport chain consists of a group of protein molecules attached to the inner membrane of the mitochondria. There are many of these chains in a cell. 1.NADH and FADH 2, from glycolysis and the citric acid cycle release high-energy electrons and pass them to the electron transport chains. 2.The electrons begin in a high-energy state. As they flow along a chain of electron acceptors, they release energy. This is used to pump hydrogen ions across the membrane from the matrix side to the inter-membrane space to maintain a higher concentration of hydrogen ions. CfE Higher Biology Metabolism and Survival

CfE Higher Biology Metabolism and Survival 3.When the hydrogen ions flow back down the concentration gradient to the matrix they pass through molecules of ATP synthase. This drives this enzyme to synthesise ATP from ADP and P i. 4.Most of the ATP generated by cellular respiration is produced in mitochondria in this way. 5.When the electrons come to the end of the electron transport chain they combine with oxygen – the final hydrogen acceptor. At the same time, the oxygen joins to a pair of hydrogen ions to form water. In the absence of oxygen the electron transport chains do not proceed and ATP is not made at this stage.

CfE Higher Biology Metabolism and Survival

Substrates for respiration - carbohydrates glucosemaltose starch glycogen sucrose fructose pyruvate

Substrates for respiration - fats Fat Glycerol Fatty acids glucose intermediate pyruvate acetyl coenzyme A Citric acid cycle

Substrates for respiration - proteins Protein Amino acids glucose pyruvat e acetyl coenzyme A Citric acid cycle Amino acids intermediate urea deamination of amino acid to respiratory pathway intermediate

Absence of Oxygen CfE Higher Biology Metabolism and Survival In the electron transport chain, oxygen and water combine to form metabolic or respiratory water. If oxygen is not present to act as the final hydrogen acceptor, then the hydrogen cannot pass through the system and complete oxidation cannot occur.

Fermentation CfE Higher Biology Metabolism and Survival There is no oxygen present in anaerobic respiration and therefore no oxygen to act as the final hydrogen acceptor. Hydrogen cannot pass through the electron transport chain. This means that both the citric acid cycle and electron transport chain cannot take place. Glucose is only partially broken down and the only ATP produced is from glycolysis. This means that only 2 ATP are produced from one molecule of glucose that undergoes respiration.