1. electron transport chain

ELECTRON TRANSPORT CHAIN

• throughout stages of respiration so far, many coenzymes (NAD and FAD) have been reduced as they accepted H

• these coenzymes are transported to ETC at cristae where they release this H and reoxidised

• H atoms split into protons (H+ ions) and electrons

• electrons passed along a series of electron carriers embedded in inner membrane of cristae and release energy which powers production of ATP- known as ‘oxidative phosphorylation’ because it depends on presence of O2

ELECTRON CHAIN TRANSPORT- DIAGRAM

ELECTRON CARRIERS- NAD

• each carrier is at lower energy level than one before

• electrons from reduced NAD are accepted by next carrier in chain, then passed along chain

• energy released by the electrons as they move down energy levels is used to drive ATP synthesis

• scientists believe its likely to be 5 ATP molecules synthesized for every 2 reduced NAD that is reoxidised

ELECTRON CARRIERS-FAD

• coenzyme FAD is associated with second carrier in chain

• scientists believe its likely to be 3 ATP molecules synthesised for every 2 reduced FAD that’s reoxidised

ELECTRON CARRIERS

• cytochromes are protein pigments w/ an iron group

• cytochrome oxidase is an enzyme

• both these carriers are reduced and oxidised as they accept then lose electrons

FINAL ELECTRON ACCEPTOR

• O2 accepts electrons at end of chain

• O2 also accepts H+ ions

• so O2 is reduced and water is formed

CHEMIOSMOSIS

• proposed by Peter Mitchell

• theory suggests that energy provided by electrons is used to actively transport H+ ions (protons) in matrix across inner membrane into intermembrane space

• now a conc gradient between intermembrane space and matrix

• also pH gradient and electrochemical gradient

• so protons want to diffuse back into matrix

• but bc inner membrane is generally impermeable to protons, only way they can move down the gradient is through special pores that span inner membrane

PORES

• these pores (or channels) are part of stalked particles embedded in inner membrane

• stalked particles are associated with ATPase enzyme

• as H+ ions flow through channels down their electrical, pH and conc gradients, they drive rotation part of enzyme and join ADP + Pi to form ATP

ETC EVIDENCE

• if you break open cells to isolate mitochondria, mitochondria will produce ATP if supplied with glucose and oxygen

• electron microscopes show inner mitochondrial membrane to be covered in stalked particles that greatly increase SA for enzyme action

• stalked particles and membranes associated with them that have been separated from rest of mitochondria are shown to be capable of ATP synthesis