BGM1002/L22 Citric Acid Cycle Flashcards
Why are metabolic pathways tightly regulated? (4)
To link supply with demand
To allow cells to respond to environmental change
To maintain a constant internal environment
To enable different tissues to interact
Give 4 ways in which glycolysis is controlled.
Rate-limiting enzymes
Enzymes at start or branch in pathways
Conformational change
Covalent modification
Compartmentalisation of enzymes/substrates
Give an example of conformational change in glycolysis regulation.
Allosteric control - non-covalent binding/release of effector molecule
Give an example of covalent modification of enzymes.
Phosphorylation of kinase
How would enzymes at the start of a pathway be regulated?
Control activity (fast)
Control synthesis (slow)
Where does glycolysis occur?
Cytosol
What is the role of adenylate kinase?
Turn 2 ADPs into ATP and AMP
Name an allosteric activator for phosphofructokinase.
Fructose-2,6-bisphosphate
How does pH affect glycolysis?
When acidic intermediates accumulate, pH falls and inhibits glycolysis
Name an inhibitor of phosphofructokinase.
Citrate
Where does the citric acid cycle occur?
In mitochondria
Give an example of compartmentalisation of substrates.
Glucose breakdown can only occur if insulin promotes uptake of glucose by a cell
What enzyme converts pyruvate into Acetyl CoA?
Pyruvate dehydrogenase
What is the byproduct of oxidative decarboxylation?
CO2
What does pyruvate dehydrogenase require? (2)
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase
What vitamins are required for the citric acid cycle? (3)
B1
Riboflavin
Niacin
Give 3 symptoms of vitamin B1 deficiency.
Loss of appetite
Lassitude
Numbness of limbs and extremities
Atropy
Where is thiamine found?
Grain husks
Meat
Name 2 types of vitamin B1 deficiency.
Beri-Beri
Wernicke-Korsakoff encephalopathy
Give 3 fates of pyruvate.
Citric acid cycle
Converted to fatty acids
Converted to amino acids
Converted to lactate
Converted to ethanol
How is pyruvate converted to amino acids?
During anabolic growth, amination to non-essential amino acids occurs
How is pyruvate converted to lactate?
Under anaerobic conditions, NAD+ regenerated
In step 6, NAD+ converts to NADH via lactate dehydrogenase
What enzyme converts pyruvate into lactate?
Lactate dehydrogenase
How is pyruvate converted to ethanol?
Under anaerobic conditions to regenerate NAD+
What is the purpose of the Krebs cycle?
Harvest high-energy electrons from carbon fuels
What are the products of one Krebs cycle?
3NADH
FADH2
2CO2
GTP
Give the intermediates of the Krebs cycle, starting from pyruvate. (7)
Pyruvate
Acetyl CoA
Citrate
Isocitrate
A-ketoglutarate
Succinyl CoA
Oxaloacetate
Why is the Krebs cycle described as amphibolic?
Involves both catabolism and anabolism
What are the products of the Krebs cycle from 2 pyruvates?
4CO2
6NADH
2FADH2
2GTP
What enzyme converts citrate to isocitrate?
Aconitase
What enzyme converts isocitrate to a-ketoglutarate?
Isocitrate dehydrogenase
What enzyme converts a-ketoglutarate to succinyl CoA?
a-ketoglutarate dehydrogenase complex
What enzyme converts succinyl CoA to succinate?
Succinyl CoA synthetase
What enzyme converts succinate to fumerate?
Succinate dehydrogenase
What enzyme converts fumarate to malate?
Fumarase
What enzyme converts malate to oxaloacetate?
Malate dehydrogenase
What enzyme converts oxaloacetate to citrate?
Citrate synthase
Give a pneumonic to remember the intermediates of the citric acid cycle.
Organic Acid Chemistry Is a Kangaroo Science Subject For Me
What enzyme can produce oxaloacetate directly from pyruvate?
Pyruvate carboxylase
Why is the citric acid cycle described as amphibolic?
It contains both catabolic and anabolic reactions
