Making ATP (F1 8/12)

Question 1

LO’s

Answer 1

1. Describe the process of oxidative decarboxylation
2. Describe the function of the Krebs cycle
3. Describe ATP production by the electron transport chain and oxidative phosphorylation
4. Describe the effects on ATP production when the electron transport chain is inhibited (e.g. cyanide, carbon monoxide poisoning)
5. Describe the function of uncoupling proteins in thermogenesis

Question 2

Glucokinase vs Hexokinase

Answer 2

• Glucokinase works in the liver to convert gluose to glucose-6-phosphate, and then to other molecules, like triglycerides and glycogen. This means that as glucose concentration increases, so does glucokinase activity.
• Hexokinase works in all other tissues to convert gluose to glucose-6-phosphate for energy. It only works at low glucose concentrations, so that excess glucose is converted by glucokinase into stored energy like glycogen.

Question 3

Fructose Metabolism

Answer 3

• Unlike glucose, which is metabolized widely in the body, fructose is metabolized almost completely in the liver, where it is directed toward replenishment of liver glycogen and triglyceride synthesis.
• First, fructose is phosphorylated into fructose phosphate by the fructokinase enzyme.
• Then, fructose phosphate is hydrolysed by adolase B to DHAP and glyceraldehyde.
• DHAP and glyceraldehyde are then converted to glyceraldehyde 3 phosphate which can be made into pyruvate.
• Essential fructosuria (fructose in urea) is caused by mutations in the fructokinase enzyme.
• Heradatory Fructose Intolerance is caused by a mutation in the Adolase- B enzyme.

Question 4

Oxidative Decarboxylation/ Link Reaction

Answer 4

1. Pyruvate enters mitochondria
2. Pyruvate converted to acetyl coA by pyruvate dehydrogenase complex.
3. Acetyl coA can be used in the Krebs cycle or as a building block for fatty acids.
4. It generates NADH and CO2
5. Pyruvate + CoA + NAD+ = Acetyl coA + CO2 + NADH
6. Catalysed by pyruvate dehydrogenase complex

Question 5

How is oxidative decarboxylation/ the link reaction regulated?

Answer 5

• The enzyme which cataylses the conversion of pyruvate + CoA + NAD+ = Acetyl CoA + NADH + CO2 is Pyruvate Dehydrogenase Complex.
• PDH complex is inactivated by pyruvate kinase. Pyruvate kinase adds a phosphate group to PDC, which stops it working. It does this when cell energy levels are high, indicated by high ATP, NADH, acetyl coA levels.
• PDH complex is activated by PDH phosphatase when energy levels are low. It takes phosphate off PDH complex, sppeding up oxi.car. PDH phosphatase activates PDH complex, when skeletal muscle is exercising and so intracellular calcium levels are high.

Question 6

The Krebs Cycle

Answer 6

• Provides energy for the majority of ATP production.
• Happens in the mitochondrial matrix (mitochondrial cytoplasm).
• When cell energy levels are low, ADP and calcium levels are high. This speeds up/up-regulates the krebs cycle.
• When NADH and ATP levels are high, the Krebs cycle is down regulated.

1. Acetyl coA enters the krebs cyle and loses its coA to become citrate. During the cycle, each acetyl coA produces 3xNADH and 1xFADH2 and GDP.

Question 7

Oxidative Phosphorylation

Answer 7

• Take electrons from NADH and FADH2 and use them to make ATP.
• Takes place on the inner membrane of the mitochodria.
• There are four membrane protein complexes on the inner membrane that form the electron transport chain.
  
  • Complex 1 is NADH hydrogenase. This complex accepts electrons from NADH.
  • Complex 2 is succinate dehydrogenase. Accepts the electrons from FADH2.
  • Complex 3 is cytochrome bc1.
  • Complex 4 is cytochrome c oxidase.
• There are also two mobile charge carriers: Co enxyme q and cytochrome c.
• The final electron acceptor is oxygen. Oxygen drags the electrons along the chain because it is a very stron acceptor.
• When the electrons are moved across the chain, some energy is spilt, like buckets of water being passed along. This allows the proteins to move protons from the matrix/cytoplasm of the mitochondria to the inter membrane space.
• There is a high concentration of protons in the intermembrane space and low conc in the matric. This gradient is called Proton Motive Force.
• This drives protons back into the matrix using ATP synthase/ Complex 5. This allows ADP to become ATP.

Question 8

ATP yeild per stage of respiration?

Answer 8

36 ATP/ glucose molecule overall:

• Glycolsis: 2 ATP from phosphate level phosphorylation, and 2 NADH, which wil go on to make 6 ATP. However, energy is required to move NADH to mitochondria from cytosol so actually only makes 4 ATP.
• Oxidative Decarboxylation: Per glucose makes 2 NADH, which will go on to make 6 ATP.
• Krebs Cycle: makes 2 ATP from substrate level phosphorylation, and makes 6 NADH and 2 FADH2 per glucose, which will go on to make 22 ATP.

Question 9

Inhibitors of Oxidative Phosphorylation

Answer 9

• CO and CN stop the transfer of electrons from complex 4 to oxygen. ATP production ceases, and cell death ocurs.
• Oligomycin stops protons moving through compex 5, so no electrochemical gradient, no ATP.
• Dinitrophenol allows protons to pass through the inner membrane, without having to use ATP synthase. No ATP made.

Question 10

What is Uncoupling Proton Thermogenesis?

Answer 10

• Uncoupling proteins are protein channels or transporters. They cause a proton leak, as cause protons to bypass complex 5/ ATP synthase, move through uncouplinng proteins instead and produce heat. So cause uncoupling.
• Thermogenin/ UCP1 generates heates in brown adipocytes in humans.
• This process in known as non-shivering thermogenesis.

Question 11

In oxidative phosphorylation, how much ATP does each NADH and FADH2 give?

Answer 11

1 NADH = 3 ATP

1 FADH2 = 2 ATP