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2.8: Cell respiration Recap: structure of ATP P P P ribose guanine inorganic phosphate deoxyribose thymine organic phosphate nicotinamide cytosine adenine flavine ATP is a source of energy Energy is released when ATP spits and forms ADP. The energy from this split is immediately available. A lot of the energy produced by cells ends up as heat (environment) therefore the body needs a continual source of energy. Cell respiration ATP ADP Cell processes (active) Redox Reactions • Oxidation – Loss of electrons – Loss of hydrogen atoms OIL RIG • Reduction – Gain of electrons – Gain hydrogen atoms • If one substrate becomes oxidised another becomes reduced. Oxidation and reduction always occur together. Co-enzymes • During respiration, hydrogen atoms are removed from substrate molecules in oxidation reactions. • This is catalysed by dehydrogenase enzymes • Co-enzymes are required to activate the oxidation reactions in respiration – Hydrogen atoms becomes attached to co enzymes e.g. NAD NAD • Nicotinamide adenine dinucleotide (NAD) – Is reduced when it has accepted two hydrogen atoms with their electrons – Operates in glycolysis, link reaction, the Krebs cycle and the anaerobic pathways. Co-enzyme A • Function – To carry ethanoate (acetate) groups made in the link reaction, onto the Krebs cycle – To carry acetate groups made from fatty acids or amino acids onto the Krebs cycle Glycolysis • Ancient biochemical pathway • Glucose (6C) is broken down into two molecules of pyruvate (3C), with a net gain of 2 ATP molecules. • Occurs in the cytoplasm • Glycolysis does not require oxygen Glycolysis • Pathway has four stages: – Phosphorylation (movement of phosphate) – Splitting of hexose 1,6-bisphosphate – Oxidation of triose phosphate – Conversion of triose phosphate to pyruvate Products of Glycolysis • Net gain of two ATP molecules • Two molecules of reduced NAD • Two molecules of pyruvate Glycolysis video – detailed. • http://highered.mheducation.com/sites/007 2507470/student_view0/chapter25/animati on__how_glycolysis_works.html Recap: where in the cell? 1. Glycolysis 1. Phosphorylation 2. Oxidation 2. Link reaction 3. Krebs cycle 4. Oxidative phosphorylation Matrix Enzymes for Krebs cycle & Link reaction Outer membrane Creates cellular compartment Ribosome DNA Expression of mitochondrial genes Intermembrane space Protons pumped into space by ETC Cristae Increase SA for oxidative phosphorylation Inner mitochondrial membrane ETC and ATP synthase The Link reaction The Link Reaction • Pyruvate is actively transported into the matrix of the mitochondria. • Pyruvate is dehydrogenated and decarboxylated to acetate in a series of enzyme controlled reactions. • Enzymes (you do not need to name these!) – Pyruvate dehydrogenase – Pyruvate decarboxylase Main points of The Link reaction 1. NAD accepts the hydrogen ions 2. Co-enzyme A accepts acetate to form Acetyl CoA, to carry onto the Krebs cycle. 3. Carbon dioxide is released Recap: Krebs cycle Krebs Cycle • Takes place in the mitochondrial matrix • Main stages – Decarboxylation • Removal of Co2 – Dehydrogenation • reduction of NAD – Substrate-level phosphorylation • Production of ATP Krebs cycle • For each original glucose molecule there are two turns of the Krebs cycle. • Products – 6 reduced NAD – 2 reduced FAD – 4 carbon dioxide – 2 ATP – Although oxygen is not used up in these stages, they can not take place if it is absent – they are aerobic stages Krebs cycle video – detailed • http://highered.mheducation.com/sites/007 2507470/student_view0/chapter25/animati on__how_the_krebs_cycle_works__quiz_ 1_.html Products of Aerobic respiration Product per molecule of glucose Reduced NAD Reduced FAD CO2 ATP Glycolysis Link reaction Krebs cycle Products of Aerobic respiration Product per molecule of glucose Reduced NAD Glycolysis Link reaction Krebs cycle 2 2 6 Reduced FAD 0 0 2 CO2 0 2 4 ATP 2 0 2 The electron transport chain The electron transport chain 1. Hydrogen atoms released from NADH and FADH as they are oxidised 2. Hydrogen atoms split into protons and electrons 3. Electrons move along the electron transport chain, losing energy at each carrier 4. Energy is used to pump protons into intermembrane space forming an electrochemical gradient 5. Protons move down electrochemical gradient back to matrix via ATP synthase 6. Movement of protons drives synthesis of ATP from ADP and inorganic phosphate 7. Protons, electrons and oxygen combine to form water, the final electron acceptor ETC video - detail • http://highered.mheducation.com/sites/007 2507470/student_view0/chapter25/animati on__electron_transport_system_and_atp_ synthesis__quiz_1_.html Evidence for chemiosmosis 1. pH of intermembrane space is lower than pH of matrix – Proton gradient exists between intermembrane space and matrix 2. Artificial vesicles created with proton pump proteins resulted in ↓ pH in vesicle – Proton gradient can be used to synthesise ATP 3. Mitochondria in pH8 solution produced no ATP – Proton gradient can be used by mitochondria to make ATP 4. Uncouplers destroyed proton gradient in mitochondria – Proton gradient is required by mitochondria to make ATP