Role of ATP in metabolism Energy Release Role of ATP in metabolism Mr G Davidson

Role of ATP in metabolism A.T.P – adenosine tri-phosphate is a molecule composed of adenosine and three phosphates. Energy is fixed into the molecule when the bond joining the terminal phosphate to the rest of the molecule is made. Friday, 18 January 2019 G Davidson

Role of ATP in metabolism The synthesis of A.T.P by the making of the bond is called phosphorylation and is achieved by linking inorganic phosphate to adenosine phosphate (A.D.P). This process occurs in the cells when an energy-rich compound such as glucose is broken down by enzymes during respiration. Friday, 18 January 2019 G Davidson

Adenosine Tri-Phosphate Adenosine di-phosphate Phosphate Adenosine tri-phosphate High energy bond Friday, 18 January 2019 G Davidson

Role of ATP in Metabolism Metabolism refers to the build up and break down of A.T.P in cells. It is usually thought of as a combination of A.T.P making reactions known as anabolism and A.T.P breaking reactions known as catabolism. Friday, 18 January 2019 G Davidson

Role of ATP in Metabolism These metabolic reactions are usually associated with the transfer of hydrogen from molecule to molecule. When a molecule gains hydrogen it is said to become reduced and if the molecule loses hydrogen it is said to become oxidised. Friday, 18 January 2019 G Davidson

Mitochondrion Structure The mitochondria are sausage-shaped organelles found in the cytoplasm, and when oxygen is present, aerobic respiration occurs here. The mitochondrion is surrounded by a double unit membrane, the inner membrane being folded into cristae which give it a larger surface area. Friday, 18 January 2019 G Davidson

Mitochondrion Structure Matrix Friday, 18 January 2019 G Davidson

Mitochondrion Structure The cristae protrude into the matrix which is a fluid filled cavity containing enzymes. The surface of the cristae are covered with many stalked particles which are the site of A.T.P production. Friday, 18 January 2019 G Davidson

Chemistry of Respiration Respiration occurs in all living cells, plant and animal, and involves chemical energy being released from food by the oxidation of glucose . There are two stages to respiration glycolysis which occurs in the cytoplasm of cells and Kreb’s (citric acid, tricarboxylic acid) cycle which occurs in the mitochondria. Friday, 18 January 2019 G Davidson

Respiration Occur in cytoplasm Friday, 18 January 2019 G Davidson

Glycolysis The first step in the release of energy from glucose is an anaerobic reaction called glycolysis which occurs in the cytoplasm. Glucose + Oxygen → Carbon Dioxide + Water + Energy C6H12O6 6O2 6CO2 6H2O A.T.P Friday, 18 January 2019 G Davidson

Glycolysis x2 x4 GLUCOSE (6C) ATP ADP + P NAD NADH2 PYRUVIC ACID (3C) Friday, 18 January 2019 G Davidson

Glycolysis The 6 carbon glucose is broken down by a series of reactions into 2 molecules of 3 carbon pyruvic acid. This process produces a net gain of 2 A.T.P molecules and hydrogen atoms which are accepted by N.A.D. The whole process of glycolysis does not require oxygen – it is only at the next stage that respiration is either aerobic or anaerobic. Friday, 18 January 2019 G Davidson

Kreb’s Cycle PYRUVIC ACID ACETYL-CO ENZYME A (2C) x2 OXALO-ACETIC CITRIC ACID (6C) 5C COMPOUND OXALO-ACETIC ACID (4C) NAD NADH2 CO2 ATP ADP + Pi x2 Friday, 18 January 2019 G Davidson

Kreb’s Cycle After glycolysis, Kreb’s cycle can only proceed if oxygen is present. The 3 carbon pyruvic acid moves into the matrix of the mitochondria where it is converted to 2 carbon acetyl co-enzyme A. This releases CO2 which is waste and hydrogen which joins the acceptor N.A.D.. Friday, 18 January 2019 G Davidson

Kreb’s Cycle The acetyl coA now joins the 4C compound oxalo-acetic acid to form 6 carbon citric acid. The citric acid is then broken down step by step by enzymes back to oxalo-acetic acid. These reactions release hydrogen, CO2 and energy. Friday, 18 January 2019 G Davidson

Cytochrome System ADP + Pi ATP NAD NADH2 Hydrogen carrier Water Oxygen From all stages NAD NADH2 Hydrogen carrier Water Oxygen Friday, 18 January 2019 G Davidson

Cytochrome System During both glycolysis and the Kreb’s cycle many compounds are oxidised by the removal of hydrogen. Friday, 18 January 2019 G Davidson

Cytochrome System This hydrogen never occurs as free atoms or molecules but is immediately used to reduce hydrogen acceptor molecules. The hydrogen is, in fact, passed through a series of acceptor molecules known as the Cytochrome system or “carrier chain”, before finally combining with oxygen to be released as water. Friday, 18 January 2019 G Davidson

Cytochrome System The movement of the hydrogen through the system is accompanied by A.T.P. production. The complete oxidation of one glucose molecule produces a total of 38 A.T.P. molecules. The hydrogen carrier system occurs in the cristae of the mitochondria. Friday, 18 January 2019 G Davidson

Studying Respiration The steps of respiration can be studied by stopping one or more of the reactions using inhibitors or metabolic poisons, e.g. salts of heavy metals such as lead and cyanide. Catechol oxidase is an enzyme which causes apple to turn brown in the presence of oxygen. Friday, 18 January 2019 G Davidson

Studying Respiration Lead nitrate is an inhibitor which prevents catechol oxidase from performing properly and therefore the apple does not turn brown. Another method of studying aerobic respiration is to measure the rate of oxygen uptake using devices known as respirometers. Friday, 18 January 2019 G Davidson

Studying Respiration These can be set up in various ways, but they nearly all use the same principle. A substance, usually a strong alkali like sodium hydroxide (NaOH) is placed in a sealed container along with a living organism. Friday, 18 January 2019 G Davidson

Studying Respiration The alkali absorbs any CO2 produced by the organism. The oxygen used up by the organism causes a reduction of volume and pressure of gas inside the container and this is measured in one of a number of ways. If the time elapsed during the experiment is also measured, then a value for the quantity of oxygen absorbed per unit of time can be measured. Friday, 18 January 2019 G Davidson

Studying Respiration Friday, 18 January 2019 G Davidson

Anaerobic Respiration This is respiration in the absence of oxygen. Some cells respire this way e.g. yeast to produce alcohol. This is anaerobic respiration in plants. Once the ethanol is produced the plant cells cannot reverse the process. Glucose pyruvic acid ethanol + CO2 Friday, 18 January 2019 G Davidson

Anaerobic Respiration Our own muscles can work without oxygen for short spells during vigorous exercise. However, the oxygen must be “paid back”, e.g. heavy breathing and panting after exercise. Friday, 18 January 2019 G Davidson

Anaerobic Respiration Glucose pyruvic acid lactic acid A build up of lactic acid leads to cramp which then prevents the muscle cells from doing any more. The body is then said to have an oxygen debt which has to be repaid to break down the lactic acid back to pyruvic acid, and therefore, this process is reversible. Friday, 18 January 2019 G Davidson