Intro to metabolism

Question 1

What is catabolism?

Answer 1

Reactions which break down molecules
-releases energy
-oxidise subsrate

Question 2

What is anabolism?

Answer 2

Reactions which build up molecules
-use energy
-reduce substrate

Question 3

Why is ATP typically used as an energy source in reactions?

Answer 3

P-O bond is strong, so when it is broken to release the γ phosphate, energy is released
-negative charges of phosphates repel eachother so when one is broken off, free energy is released

Question 4

What is the importance of carbon dioxide in reactions?

Answer 4

-CO2 is very stable
-CO2 escapes very readily from rxn site, maintains low conc so pulls rxn to right (law of mass action)
-when CO2 is produced, tend to end up with more molecules than started with, meaning entropy is favourable

∴rxns which release CO2 tend to be energetically favourable

Question 5

Where do carbon atoms in metabolic flux come from?

Answer 5

Humans obtain C from food -ultimately from photosynthesis
-plants fix CO2

Anapleurotic reaction of pyruvate conversion to OAA (using ATP) also fixes CO2 (done in humans)
-tops up TCA cycle

Question 6

Where do oxygen atoms in metabolic flux come from?

Answer 6

water or 02

Question 6

Where do hydrogen atoms in metabolic flux come from?

Answer 6

water

Question 7

Where do nitrogen atoms in metabolic flux come from?

Answer 7

Humans obtain N from food -ultimately from N2 fixation
-plants and bacteria convert N2 to ammonia, nitrates and nitrites

We then convert ammonia to glutamate by reacting it with α-ketoglutarate

Question 8

What are threshold enzymes?

Answer 8

Enzymes which bring key elements (C, N, H, O) into biosynthetic pathways
-highly controlled
-high affinity for substrate
-non-constitutive (regulated by cell, obtain elements as needed)
eg. pyruvate carboxylase (C), glutamate dehydrogenase (N)

Question 9

What is metabolic flux?

Answer 9

Molecule turnover
Atom conservation