Energy Production - TCA cycle Flashcards
WHere does the TCA cycle take place?
Mitochondria
What is the main substances needed by the pathway?
The pathway requires NAD+, FAD and oxaloacetate.
What is the main function of the TCA cycle?
The main function of the pathway is to break the C-C bond in acetate (as acetyl~CoA) and oxidise the C-atoms to CO2.
The H+ and e- removed from acetate are transferred to NAD+ and FAD.
Can this reaction take place in the absence of oxygen?
No
Why are there no known genetic defects in the pathway?
It would be lethel
What is the role of pyruvate dehydrogenase (PDH) in the TCA cycles?
Pyruvate transported from cytoplasm across mitochondrial
membrane
PDH is a large multi-enzyme complex (5 enzymes) that converts pyruvate Acetyl coA which is used in the TCA cycle
What activates and inhibits PDH?
activated by: Pyruvate CoASH NAD+ ADP Insulin dephosphorylation
inhibited by: acetyl-CoA NADH ATP citrate phosphorylation
How does PDH work?
It converts pyruvate to acetyl coA via irreversible loss of Co2
The different enzyme activities require various cofactors (FAD,
thiamine pyrophosphate and lipoic acid).
B-vitamins provide
these factors, so reaction is sensitive to Vitamin B1 deficiency.
Reaction is irreversible, so is a key regulatory step and pyruvate therefore cannot be formed from Acetyl CoA
What disease does PDH deficiency lead to?
Lactic acidosis
How is the TCA cycle regulated?
It’s oxidative - requires oxygen
It’s s ingle pathway
It is activated and inhibited by various molecules
Pyruvate is converted to Acetyl coA in an irreversible reaction
It is regulated by energy availability - increase in NADH succinyl-CoA and ATP leads to inhibition and increase in ADP leads to activation
How many cycles of the TCA cycle are there?
2 cycles for every glucose entering glycolysis
Which enzymes in the cycle regulate the TCA cycle?
a-ketoglutarate dehydrogenase
- - NADH, ATP,
succinyl-CoA
Isocitrate dehydrogenase
- One of the early irreversible steps of the TCA cycle (catalysed by isocitrate dehydrogenase) is allosterically inhibited by the high-energy signal NADH and activated by the low-energy signal ADP.
Which precursors for biosynthesis
does the TCA cycle produce?
Fatty acids
Amino acids
Haem synthesis
Glucose
Describe the roles of the tricarboxylic acid cycle (TCA cycle) in
metabolism.
• Mitochondrial
• Central pathway in the catabolism of sugars, fatty acids, ketone
bodies, amino acids, alcohol
- Strategy - to produce molecules that readily lose CO2
- Breaks C-C bond in acetate (acetyl~CoA); carbons oxidised to CO
- Oxidative producing NADH and FADH
- Some energy as GTP ( ATP) produced directly
- Produces precursors for biosynthesis
- Does not function in absence of O
• Intermediates act catalytically - no net synthesis or degradation of
Krebs cycle intermediates alone
List the end-products of glycolysis under aerobic and anaerobic conditions in red blood cells and skeletal muscle.
-
