The Link Reaction & Kreb's Cycle & Oxidative Phosphorylation

Question 1

What are the 2 steps in the formation of acetate in the Link Reaction?

Answer 1

• Decarboxylation

- Dehydrogenation/oxidation

Question 2

Is there any ATP produced in the Link Reaction?

Answer 2

No

Question 3

What is formed from pyruvate in the Link reaction?

Answer 3

• Acetate

Question 4

How is acetate formed from pyruvate in the link reaction?

Answer 4

• Decarboxylation: Removal of a carbon
• CO2 removed as waste product
• Dehydrogenation: 2Hs are removed and taken up by NAD to produce reduced NAD

Question 5

How is acetate turned into acetyl coA?

Answer 5

Combines with co enzyme A [CoA]

Question 6

How many carbons does acetate contain?

Answer 6

2

Question 7

How many carbons does acetyl coA contain?

Answer 7

2

Question 8

How many carbons does pyruvate contain?

Answer 8

3

Question 9

Where does the link reaction occur?

Answer 9

Mitochondrial matrix

Question 10

How many times does the link reaction happen per glucose and why?

Answer 10

Twice because 2 pyruvate molecules produced from each

Question 11

What are the products of the Link reaction per glucose?

Answer 11

• 2x acetyl coA
• 2 reduced NAD
• 2 Co2

Question 12

What are the products of the Link reaction per glucose and where do they go?

Answer 12

• 2x acetyl coA: Kreb’s cycle
• 2 reduced NAD: co-enzyme for ATP production in oxidative phosphorylation
• 2 CO2: waste product

Question 13

Where does the Kreb’s cycle happen?

Answer 13

Mitochondrial matrix

Question 14

How many times does the Kreb’s cycle happen per pyruvate and therefore glucose?

Answer 14

• Once per pyruvate

- Twice per glucose

Question 15

Describe what happens in the Kreb’s cycle - 10

Answer 15

• Acetyl CoA combines with 4C compound to form 6C compound.
• Co-enzyme A is released and goes back to the link reaction to be used
• 6c Compound is converted to a 5 carbon intermediate compound
• Decarboxylation occurs and Co2 is produced
• Dehydrogenation occurs so H2 is removed
• Reduces NAD to reduced NAD
• 5C compound is converted to a 4 C compound
• Dehydrogenation and decarboxylation occur to produce 1x reduced FAD and 2x reduced NAD
• ATP is produced from direct transfer of a phosphate group from 5 intermediate carbon compound to ADP - substrate level phosphorylation
• 6C compound has now been concerted to 4C compound
• Combines with Acetyl CoA again

Question 16

What happens in the Link Reaction overall?

Answer 16

• Acetyl coA combines with a 4 carbon compound to form 6 carbon compound which is then recoverted into 4 carbon compound
• Co enzymes are formed to be used in oxidative phosphorylation

Question 17

What are the products of the Link Reaction and where do they go?

Answer 17

• 1x co enzyme A : reused in link reaction
• 1x reduced FAD and 3x reduced NAD : co enzymes for oxidative phosphorylation for ATP production
• 1x 4 carbon compound reused in cycle
• 2xCO2 : released as waste product

Question 18

Where does oxidative phosphorylation?

Answer 18

Inner membrane of cristae of mitochondria

Question 19

How is the structure of cristate adapted for odixative phosphorylation?

Answer 19

Increases surface area for maximum efficiency

Question 20

What is the electron transport chain formed from?

Answer 20

A series of proteins bound to the inner mitochondrial membrane

Question 21

Explain oxidative phosphorylation

Answer 21

• First protein in the ETC oxidises reduced FAD and reduced NAD to FAD and NAD
• Hydrogen atoms produced
• H atoms are split into H+ ions and electrons that bind to the protein
• Electrons move down ETC passing from one electron to carrier to the next, losing energy as they do
• This is a series of redox reactions as carrier is oxidised/reduced
• This energy is used by electron carriers to pump H+ ions across from the matrix across the inner mitochondrial membrane into intermembrane space
• Rest lost as heat
• Concentration of protons in intermembrane space is higher than matrix
• Forms steep electrochemical gradient across membrane
• H+ ions diffuse down electrochemical gradient through hollow protein channel in ATP synthase back into matrix
• This movement drives the synthesis of ATP from ADP and Pi catalysed by ATP synthase : chemiosmosis
• The final protein in the ETC donates an electron pair to an oxygen atom in the blood
• This is the final proton and electron acceptor and so is reduced to form water

Question 22

How does ATP synthase catalyse the formation of ATP? 2

Answer 22

• H+ ions change the enzyme active site,

- Enables ADP and Pi to bind to it

Question 23

What do metabolic poisons target?

Answer 23

The electron carriers in oxidative phosphorylation

Question 24

What are the consequences of metabolic poisoning? 7

Answer 24

• Carriers can’t pass on electrons
• Stops them moving down ETC
• Stops chemiosmosis
• Reduced NAD and reduced FAD no longer oxidised
• No FAD and NAD regenerated for Kreb’s cycle
• Kreb’s Cycle stops
• ATP synthesis in cell is highly reduced

Question 25

How many ATP molecules made by each reduced FAD?

Answer 25

2

Question 26

How many ATP molecules made by each reduced NAD?

Answer 26

3

Question 27

How many ATP molecules made in per glucose molecule in the Kreb’s Cycle?

Answer 27

2

Question 28

How many ATP is estimated to be produced by each glucose?

Answer 28

38

Question 29

Why is the theoretical yield of glucose being 38 not entirely accurate?

Answer 29

Some protons are used in the exchange of ADP and ATP between matrix and cytoplasm

Question 30

Define “chemiosmosis”

Answer 30

Energy in a chemical gradient established by electron movement used to generate ATP

Question 31

What is the evidence for chemiosmosis?

Answer 31

• H+ gradient across inner membrane corresponds to a pH gradient that can be measured
• Isolated ATP synthase enzymes can produce ATP using proton gradient even if no electron transport occurring
• Chemicals blocking ETC inhibit proton gradient formation, stops ATP synthesis