The Link Reaction & Kreb's Cycle & Oxidative Phosphorylation Flashcards
What are the 2 steps in the formation of acetate in the Link Reaction?
- Decarboxylation
- Dehydrogenation/oxidation
Is there any ATP produced in the Link Reaction?
No
What is formed from pyruvate in the Link reaction?
- Acetate
How is acetate formed from pyruvate in the link reaction?
- Decarboxylation: Removal of a carbon
- CO2 removed as waste product
- Dehydrogenation: 2Hs are removed and taken up by NAD to produce reduced NAD
How is acetate turned into acetyl coA?
Combines with co enzyme A [CoA]
How many carbons does acetate contain?
2
How many carbons does acetyl coA contain?
2
How many carbons does pyruvate contain?
3
Where does the link reaction occur?
Mitochondrial matrix
How many times does the link reaction happen per glucose and why?
Twice because 2 pyruvate molecules produced from each
What are the products of the Link reaction per glucose?
- 2x acetyl coA
- 2 reduced NAD
- 2 Co2
What are the products of the Link reaction per glucose and where do they go?
- 2x acetyl coA: Kreb’s cycle
- 2 reduced NAD: co-enzyme for ATP production in oxidative phosphorylation
- 2 CO2: waste product
Where does the Kreb’s cycle happen?
Mitochondrial matrix
How many times does the Kreb’s cycle happen per pyruvate and therefore glucose?
- Once per pyruvate
- Twice per glucose
Describe what happens in the Kreb’s cycle - 10
- 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
What happens in the Link Reaction overall?
- 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
What are the products of the Link Reaction and where do they go?
- 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
Where does oxidative phosphorylation?
Inner membrane of cristae of mitochondria
How is the structure of cristate adapted for odixative phosphorylation?
Increases surface area for maximum efficiency
What is the electron transport chain formed from?
A series of proteins bound to the inner mitochondrial membrane
Explain oxidative phosphorylation
- 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
How does ATP synthase catalyse the formation of ATP? 2
- H+ ions change the enzyme active site,
- Enables ADP and Pi to bind to it
What do metabolic poisons target?
The electron carriers in oxidative phosphorylation
What are the consequences of metabolic poisoning? 7
- 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
How many ATP molecules made by each reduced FAD?
2
How many ATP molecules made by each reduced NAD?
3
How many ATP molecules made in per glucose molecule in the Kreb’s Cycle?
2
How many ATP is estimated to be produced by each glucose?
38
Why is the theoretical yield of glucose being 38 not entirely accurate?
Some protons are used in the exchange of ADP and ATP between matrix and cytoplasm
Define “chemiosmosis”
Energy in a chemical gradient established by electron movement used to generate ATP
What is the evidence for chemiosmosis?
- 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
