Electron Transport Chain

Question 1

What is the electron transport chain?

Answer 1

A series of protein carriers on the inner membranes of mitochondria and chloroplasts that release energy from electrons and incorporate it into ATP.

Question 2

Describe respiration in relation to the electron transport chain.

Answer 2

hydrogen atoms from glucose breakdown are transferred by dehydrogenase to NAD and FAD and carried to inner membrane of mitochondria - electrons and protons from hydrogen have different pathways but because they both move down the ETC the system is often described as carrying H+ - for every 2 protons delivered by NADH, 3 ATP is made - when FAD delivers 2 protons, 2 ATP is made.

Question 3

Where is the energy for the proton pump and ETC derived from?

Answer 3

Oxidation reactions ie electron loss. Phosphorylation is the addition of a phosphate group, so synthesising ATP by adding P to ADP using energy derived from phosphorylation is called oxidative phosphorylation.

Question 4

Briefly describe photosynthesis in relation to the ETC.

Answer 4

Groups of pigments and proteins called photosystems transfer excited electrons to electron acceptors and to series of protein carriers on thylakoid membranes - protons from water and electrons are transferred to NADP and then glycerate phosphate in a pathway which synthesises carbohydrates - the energy that powers the proton pumps and ETC in the chloroplast is derived from light - therefore it is called photophosphorylation

Question 5

Briefly describe ATP synthase.

Answer 5

• occurs in all bacteria, archaea and eukaryotes
• It is a nano-machine
• as protons diffuse down the electrochemical gradient through it, the energy released causes the rotor and stalk to rotate.
• The mechanical energy from this rotation is converted into chemical energy as a phosphate ion, added to ADP to form ATP in the catalytic head
• it takes 3 protons to move the rotor through 120 degrees releasing 1 ATP molecule