Citric Acid Cycle Flashcards
What is the citric acid cycle?
Breakdown of fuel molecules into carbon dioxide and water
Carbon molecules in cycle:
C2 + C4 = C6
C6 -> C5 -> C4
What’s produced in the cycle?
2x CO2
1x GTP
3xNADH
1x FADH2
What eventually happens to the FADH2 produced in the cycle?
Hydrogen combines with oxygen and forms water
This process is coupled to ATP synthesis
What does FAD stand for?
Flavin Adenine Dinucleotide
What is FAD formed from?
Vitamin riboflavin
Deficiency of riboflavin:
Lesions of mucous membranes
Where does citric acid cycle take place?
Mitochondrial MATRIX
How is pyruvate broken down to form C2?
Pyruvate broken down into Acetyl CoA by pyruvate dehydrogenase
NAD+ is converted to NADH and CO2 is released
Acetyl CoA is broken down into Acyl unit (2 carbon)
What is CoA?
Nucleotide
Contains vitamin B5
What must happen first in the cycle in regards to acyl group (C2)?
Condensation with oxaloacetate (C4)
Citrate is formed (C6)
What then happens to citrate in cycle?
Dehydrogenation
NADH and CO2 formed
C5 formed
What must happen to C5 in cycle?
Dehydrogenation
NADH and CO2 formed
CoA is needed to form C4
What then happens to C4?
- GTP formed and CoA is released
- FADH2 is formed
- NADH is formed
- Oxaloacetate is formed - cycle starts again
Where does oxidative phosphorylation take place?
Macromolecular assemblies in inner mitochondrial membrane
What essentially is oxidative phophorylation?
H+ and electrons are taken from fuel molecules by NAD+
They are passed down chain of electron-carrying molecules until passed to oxygen
Respiratory chain:
Electron transport chain
How many complexes in Respiratory chain?
4 large complexes linked by electron shuttles
What feeds electrons into respiratory chain?
NADH and FADH2
What’s complex 1 in respiratory chain?
NADH-Q reductase
Where does complex 1 send electrons?
To Q which then sends electrons to complex 3
What’s complex 2 in respiratory chain?
FADH2 in flavoproteins
Where do electrons from FADH2 go to?
To Q which then sends electrons to complex 3
What’s complex 3?
Cytochrome reductase
Where do electrons from complex 3 go to?
To Cyt C and then passed onto complex 4
What’s complex 4?
Cytochrome oxidase
Where do electrons on complex 4 go to?
Combine with oxygen
What does Q stand for?
Ubiquinone
Respiratory chain order:
NADH —> NADH-Q reductase —> Q —> Cytochrome reductase
FADH2 —>
Cytochrome Cytochrome
Reductase —> Cyt c —> oxidase ——-> O2
Inhibitors of respiratory chain:
Rotenone - insecticide
Antimycin A - Antibiotic
Carbon monoxide and cyanide
What’s important about electrons being passed from one complex to another in the chain?
Energy is released and used more efficiently
What does the respiratory chain generate?
H+ ion (pH) gradient across inner mitochondrial membrane due to movement of electrons
What’s the electrochemical gradient across inner mitochondrial membrane used for?
To drive ATP synthesis by ATP synthase
How is ATP synthase different to sodium-potassium ATPase pump?
Work in opposite directions
Na/K pump uses ATP to generate ion gradient
ATP synthase uses ion gradient to generate ATP
How much ATP does oxidation of NADH produce?
2.5
How much ATP does oxidation of FADH2 produce?
1.5
Overall net yield from citric acid cycle:
4 ATP
2 NADH - cytoplasm (breakdown of pyruvate)
8 NADH - mitochondria
2 FADH2
Note: cycle happens twice per glucose
Overall net yield from glycolysis:
2 ATP
2 NADH
Overall yield of ATP from breakdown of glucose?
32
4 ATP 25 ATP (from 10 NADH x 2.5) 3 ATP (from 2 FADH2 x 1.5)
