Oxidative phosphorylation

What is oxidative phosphorylation?

• Process where energy carried by electrons from reduced coenzymes is used to make ATP

• formation of ATP by the addition of a Pi to ADP in the presence of oxygen

What is the purpose of oxygen in oxidative phosphorylation?

it is the final electron acceptor

Where does oxidative phosphorylation take place?

in the inner mitochondrial membrane (cristae)

What is teh chemiosmotic theory of oxidative phosphorylation?

• energy released from ETC is used to pump protons against conc gradient

• into intermembrane space

• protons diffuse back into matrix through ATP synthase enzyme

How many molecules of ATP does one NAD molecule produce when entering the ETC?

2.5 molecules of ATP

How many molecules of ATP does one FAD molecule produce when entering the ETC?

1.5 molecules of ATP

What is the total ATP yield from the electron transport chain?

28 ATP

What is the overall yield of ATP from respiration of one molecule of glucose?

32 ATP

What is the overall yield of ATP from substrate level phosphorylation?

4 ATP

• 2 in glycolysis

• 1 per turn of the Krebs cycle - 2 turns

What is the overall ATP yield from oxidative phosphorylation?

28 ATP

• 5 ATP from 2 NADH produced in glycolysis

• 5 ATP from 2 NADH produced in link reaction

• 15 ATP from 6 NADH produced in Krebs

• 3 ATP from 2 FADH₂ produced in Krebs

What is the first step of the electron transport chain?

• NADH —> NAD + 2H⁺ + 2e^-

• electrons are accepted by the 1st electron carrier in the ETC

What is the second step in the ETC?

• electrons are passed from carrier to carrier

• as the electrons are moved energy is released

• coenzymes use energy to pump H⁺ from the matrix into the intermembrane space

What is the third step in the ETC?

• the electrons combine with H⁺ and oxygen to form water

• 2e^- + 4H⁺ + O₂ —> 2H₂O

• oxygen is the final electron acceptor

What is the fourth step in the ETC?

• FADH₂ —> FAD + 2H⁺ + 2e^-

• electrons released enter the ETC at complex ii

• they are passed along carriers and eventually combine with oxygen and protons to make water

What is the fifth step of the ETC?

• protons are pumped into intermembrane space during ETC

• they build us as they are unable to diffuse through the lipid part of the membrane

What is the final step of the ETC?

• protons diffuse back into the matrix

• through channels associated with ATP synthase enzymes

• causes the rotation of part of the enzyme which joins ADP and Pi to make ATP

• this is called chemiosmosis

What are some pieces of evidence for chemiosmosis?

• potential difference across the membrane - more neg on matrix side

• when headpiece of ATP synthase removed no ATP is produced

• when outer membrane is removed no ATP produced

• pH is lower in intermembrane space than matrix

• enzymes involved in the link reaction and Krebs cycle are found in matrix

• enzymes involved in ETC and OP are embedded in the inner membrane

• oligomycin blocks flow of protons - when present no ATP is generated

What conclusions can be drawn from the evidence for chemiosmosis?

• ETC and OP involve the inner mitochondrial membrane

• intermembrane space allows build up of protons and therefore an electrochemical gradient

• ATP synthase enzymes are responsible for generating ATP

• it is the flow of H⁺ across the membrane that provides the energy to generate ATP