Metabolism

Question 1

What is metabolism?

Answer 1

A network of chemical reactions carried out by living cells

Question 2

What are metabolites?

Answer 2

Small molecules that are intermediate in the biosynthesis or degradation of biopolymers

Question 3

2 main classes of metabolic pathways

Answer 3

Catabolic pathways = complex molecules broken down to release energy stored in chemical bonds

Anabolic pathways = complex molecules made from simpler ones to store energy in chemical bonds

Question 4

Single vs multi step pathways

Answer 4

• Multistep enzyme pathways release energy in smaller units so it can be used by cells
• Each reaction needs one enzyme
• Similar in all organisms but inside specific organelles in eukaryotes
• Regulated by key enzymes that cane be inhibited or activated

Question 5

Characteristics of metabolic pathways

Answer 5

1. Highly regulated —> allow response to environmental changes and avoid futile cycles
2. Often irreversible & no backing up
3. Have a flow of materials that depends on supply of substrates, removal of products (prevents accumulation) and pathway of enzyme activities

Question 6

What are the mechanisms of regulation?

Answer 6

• feedback inhibition
• feed-forward activation
• inhibition or activation from other pathways
• modulation of individual regulatory enzymes

Question 7

What is feedback inhibition?

Answer 7

Product of a pathway controls the rate of its own synthesis by inhibiting an earlier step

Question 8

What is feed-forward activation?

Answer 8

A metabolite early in the pathway activates an enzyme further down the pathway

Question 9

Describe modulation of individual regulatory enzymes

Answer 9

• allosteric inhibitors or activators cause a change in conformation and activity
• enzyme activity can be rapidly and reversibly altered by covalent modifications of the enzyme
• e.g. protein phosphorylation

Question 10

What is a coupled reaction?

Answer 10

The sum of two coupled reactions

One endergonic (does not happen on its own) and the other exergonic (happens on its own)

Question 11

What are autotrophic organisms?

Answer 11

Obtain supplies of free energy from the energy of sunlight (photosynthesis) and energy of chemical reactions (e.g. mineral sources or thermal vents)

Question 12

What are heterotrophic organisms?

Answer 12

Obtain supplies of free energy from the breakdown of complex organic molecules in other organisms

Heterotrophes (lion, zebra, bugs) need autotrophes (grass) to survive

Question 13

What is ATP?

Answer 13

All organisms use ATP for transferring free energy between reactions

In the human body, 2.3 kg of ATP is formed and consumed every day

Question 14

Interconversion between ATP and ADP

Answer 14

ATP + AMP <—> 2ADP

• Adenylate kinase interconverts adenine nucleotides at near equilibrium
• When ATP is hydrolysed rapidly in the cell, ADP levels increase and this reaction will convert some ADP back into ATP
• When the reaction moves to the left, AMP concentrations rise. This is a low energy state
• AMP acts as a metabolic signal to increase the rate of some catabolic reactions

Question 15

What are NDPs?

Answer 15

Nucleotide diphosphate kinases (NDPs) convert ATP to any other nucleotide triphosphates