3.5.2 respiration

ATP

• outer membrane • inter membrane space • inner membrane • cristae • matrix • circular DNA • 70S ribosomes • phosphate granule

the first stage of aerobic and anaerobic respiration - it occurs in the cytoplasm and is an anaerobic process

• phosphorylation of glucose to glucose phosphate using ATP • production of triose phosphate • oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD

• glucose is made more reactive by the addition of two phosphate molecules (phosphorylation) • the phosphate molecules come from the hydrolysis of two ATP molecules to ADP • the hydrolysis of ATP provides the energy to activate glucose and lowers the activation energy for the following enzyme-controlled reactions

• the phosphorylated glucose molecule is hydrolysed to product two 3-carbon molecules called triose phosphate

• hydrogen is removed from each triose phosphate molecule and transferred to a hydrogen-carrier molecule called NAD to produce reduced NAD • enzyme-controlled reactions convert each triose phosphate molecule into a 3-carbon pyruvate molecule • in this process, two molecules of ATP are regenerated from ADP (so 4 ATP molecules produced in total)

2 molecules (4 are produced but only 2 are used in the initial phosphorylation of glucose)

pyruvate + reduced NAD -> ethanol + CO2 + oxidised NAD

pyruvate + reduced NAD -> lactate + oxidised NAD

• pyruvate can be converted to lactate or ethanol using reduced NAD • the oxidised NAD produced in this way can be used in further glycolysis (as it can’t continue to oxidative phosphorylation)

pyruvate from glycolysis enters the mitochondrial matrix by active transport

the mitochondrial matrix

• pyruvate is oxidised to acetate, producing reduced NAD in the process • acetate combines with coenzyme A to produce acetylcoenzyme A

• decarboxylation of pyruvate occurs producing CO2 • pyruvate is oxidised to acetate (2 carbon molecule) • coenzyme A binds to acetate so it can be delivered to the next enzyme in the correct orientation

• acetylcoenzyme A reacts with a 4 carbon molecule releasing coenzyme A and producing a 6 carbon moleucle which enters the Krebs cycle • in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost

• the 6 carbon molecule undergoes decarboxylation (produces CO2) and is oxidised by NAD (produces reduced NAD), which forms a 5 carbon molecule • the 5 carbon molecule undergoes decarboxylation and oxidation by NAD which forms a 4 carbon molecule, and ADP and Pi form an ATP molecule • the 4 carbon molecule is oxidised by FAD producing another 4 carbon molecule which is oxidised by NAD producing a 4 carbon molecule which can react with incoming acetylcoenzyme A

the cristae

synthesis of ATP via oxidative phosphorylation is associated with the transfer of electrons down the electron transfer chain and passage of protons across inner mitochondrial membranes and is catalysed by ATP synthase embedded in these membranes

• reduced NAD/FAD donate hydrogen atoms which split into protons/hydrogen ions and electrons • the electrons move down the electron transport chain and release energy as they pass between electron carriers • the energy is used to actively transport protons across the inner membrane from the matrix to the intermembrane space • proton channels associated with ATP synthase move the protons back across the membrane via facilitated diffusion • the proton motive force causes a conformational change in the channel proteins which enables ATP synthase to catalyse the condensation of ADP and Pi to ATP • oxygen acts as the terminal electron acceptor for electrons coming off the transport chain and combines with the electrons and protons as well to form water

• the process of protons diffusing through ATP synthase down the concentration gradient • this releases energy which converts ADP and Pi to ATP

the breakdown products of lipids and amino acids, which enter the Krebs cycle

• glycerol is a 3 carbon molecule which can be converted to pyruvate • fatty acids can be 2 carbon molecules which can be converted to acetylcoenzyme A

• the deamination of amino acids produces molecules with different numbers of carbon atoms • 3 carbon molecules can be converted to pyruvate • 4 and 5 carbon molecules can enter the Krebs cycle as intermediates