Transcript Slide 1
Wednesday, July 15, 2015 Unit 4: Respiration Title: Electron transport chain Learning Objectives: We are learning…. • Where does the electron transport chain take place? • How is ATP synthesised in the electron transport chain? • What is the role of oxygen in aerobic respiration? Starter: How many of each molecule is produced during the following stages of Aerobic Respiration? Molecule ATP GLYCOLYSIS 7 LINK REACTION 0 KREBS CYCLE 2 Carbon dioxide 0 2 4 Reduced NAD 2 2 6 Reduced FAD 0 0 2 Today we will focus on the electron transport chain. The chain is a series of electron carriers found in the inner mitochondrial membrane. The membrane is folded into cristae which provide a large surface area, accommodating thousands of copies of the transport chain in each mitochondria. How does the electron transport chain work? Each carrier in the electron transport chain is reduced as it picks up electrons and oxidised as it gives up electrons. Through a series of redox reactions small amounts of energy are released. This energy is used to form ATP. In aerobic cellular respiration the final electron acceptor is oxygen. The following molecules are involved in the chain: NAD, FAD, FP (flavoprotein) CoQ (coenzyme Q), ATP The electron transport chain – step by step Reduced NAD and reduced FAD enter the chain with their hydrogen atoms attached. In the initial stages of the chain, hydrogen atoms are passed along the chain, but these later split into their protons and electrons. The protons (hydrogen ions) are actively transported across the inner mitochondrial membrane, accumulating in the space between mitochondrial membranes before diffusing back in to the matrix through protein channels (involves ATPase enzymes). The electron transport chain – step by step With the protons removed only the electrons pass from carrier to carrier. With each oxidation-reduction reaction the electrons lose energy (remember energy levels in light-dependent photosynthesis?) This energy is used to combine ADP with inorganic phosphate (Pi) to form ATP – phosphorylation. Some energy is released as heat. At the end of the chain the protons and electrons recombine, and the hydrogen atoms created link with oxygen to form water. But what if the newly formed hydrogen can’t combine with oxygen…..? The electron transport chain – step by step ATP is formed through each oxidation of a hydrogen atom – this is known as oxidative phosphorylation. The role of oxygen is to act as the final acceptor of the hydrogen atoms. If oxygen is absent, only anaerobic glycolysis can continue. Cyanide – the respiratory inhibitor The transfer of hydrogen atoms to oxygen at the end of the electron transport chain is catalysed by the enzyme cytochrome oxidase. This enzyme is inhibited by cyanide, so cyanide prevents the removal of hydrogen atoms at the end of the respiratory chain. In these circumstances the hydrogen atoms accumulate and aerobic respiration ceases. Cyanide – the respiratory inhibitor Energy yields – electron transport chain Reduced FAD 2 (from Krebs) Reduced NAD 2 (from Glycolysis) 2 (from 2x link reaction) 6 (from 2x Krebs) 1.5 X 2 = 3 ATP 2.5 X 10 = 25 ATP 3 ATP + 25 ATP = 28 ATP Add this to the 4 ATP made directly in glycolysis and krebs and you have 32 ATP altogether! Main Activity: Complete the worksheet ‘cellular respiration’ Plenary: Complete the exam question DNP inhibits respiration by preventing a proton gradient being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed • less ATP was produced • more heat was produced • the uptake of oxygen remained constant. Explain how DNP caused these changes. (3) 1. Less/no proton/H+ movement so less/no ATP produced; 2. Heat released from electron transport / redox reactions/ energy not used to produce ATP is released as heat; 3. Oxygen used as final electron acceptor/combines with electrons (and protons) How successful were we this lesson? Learning Objective We were learning….. Back