TCA cycle + Urea cycle

Question 1

Role of TCA cycle

Answer 1

1. Energy production from acetyl co-A produced from fatty acid, protein and carbohydrate
2. Biosynthesis

• ATP synthesis through 4 oxidative reactions
• common ground for interconversion of fuels to metabolites

Question 2

Interconversion of pyruvate and enzymes involved

Answer 2

Pyruvate – alanine transaminase – alanine
Pyruvate – lactate dehydrogenase –lactate
Pyruvate – pyruvate decarboxylase – oxaloacetate
Pyruvate – pyruvate dehydrogenase – acetyl co-A

Question 3

enzymes, coenzymes and vitamin involved in Pyruvate dehydrogenase complex

Answer 3

Enzymes: Pyruvate dehydrogenase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase

Co-enzymes: thiamine pyrophosphate, CoA, NAD+, FAD, Lipoamide

Vitamin: riboflavin, nicotanamide, pantothenic acid, thiamine

Question 4

TCA cycle substrate, product and ATP yield

Answer 4

Substrate - oxaloacetate and acetyl co A
Product: oxaloacetate
per mole of acetyl co - A
3 NADH, FADH2, GTP
Yield: 30-32 moles of ATP per mole of glucose

Question 5

Cataplerosis and anaplerosis

Answer 5

Cataplerosis: TCA cycle intermediates are used in biosynthesis of fuels
Anaplerosis: building up of TCA cycle intermediates

Question 6

Regulator of TCA cycle

Answer 6

Pyruvate dehydrogenase
Isocitrate dehydrogenase

Question 7

Urea cycle

Answer 7

is important for disposal of excess nitrogen in form of urea.

1. Ornithine + carbamoyl P – ornithine transcarbamoylase – Citrulline
2. Citrulline + Asparate (from TCA cycle or other AA) –argininosuccinate synthase – arginino succinate
3. Argininosuccinate – argininosuccinase –arginine + fumarate (goes to TCA cycle)
4. arginine – arginase – Ornithine + Urea (soluble, non-toxic)

Question 8

Glucogenic vs Ketogenic AA

Answer 8

This depends on at which point the carbon from AA enters TCA cycle.
Glucogenic: AA entering from alfa-ketoglutarate, succinate, fumarate, oxaloacetate and pyruvate point are used in glucose synthesis so they are glucogenic AA
Eg: alanine and others

Ketogenic: AA entering at acetyl Co-A or acetoacetyl Co-A point are involved in ketone bodies synthesis so they are ketogenic AA Eg: Leucine and lysine

Both ketogenic and glucogenic: aromatic AA (tyrosin, tryptophan and phenylalenine)

Question 9

Essential vs non-essential AA

Answer 9

Essential : not synthesized in the body and required from diet
Non-essential: synthesized in the body

Question 10

Metabolic source of non-essential AA

Answer 10

Alanine - Pyruvate
Serine - 3 phosphoglycerate
Tyrosine - from phenylalanine
Cysteine - serine but requires S from methionine
Glycine - serine
aspratic acid, arginine, glutamine, proline - TCA cycle

Question 11

Three mechanism for removal of Nitrogen from AA

Answer 11

Transamination
Oxidative deamination
Non-oxidative deamination