Metabolic regulation

Question 1

Why is metabolic regulation required ?

Answer 1

• human body requires energy to function
• body does not have a constant external supply of energy
• energy intake is intermittent but energy expenditure is continuous
• energy needs to be stored and released when required

Question 2

Give some examples of when there may be a sudden requirement for energy consumption

Answer 2

• exercise can increase metabolic rate up to 20x more than at resting level
• severe illness can increase metabolic rate

Question 3

What is metabolic regulation ?

Answer 3

• covers the distribution and storage of nutrients after meals
• includes the delivery to and utilisation in tissues and cells
• it works at a molecular level by the modulation of enzyme activities

Question 4

How is metabolism regulated ?

Answer 4

• levels and accessibility of substrates and enzymes
• amounts of metabolic enzymes
• modulation of catalytic activities of enzymes

Question 5

What determines the number of enzyme molecules available ?

Answer 5

• production of transcription factor by external factors
• stability of mRNA species
• rate of translation
• rate of protein degradation

Question 6

What is allosteric regulation ?

Answer 6

It is when a small molecule binds away from the enzyme active site and has a non covalent interaction changing the conformational structure of the protein

Question 7

What is an allosteric effector or modulator ?

Answer 7

ligands which bind to the allosteric site

Question 8

What is positive allosteric regulation ?

Answer 8

When the allosteric effector binds allowing the substrate to bind better and faster
- the allosteric effector will be an activator

Question 9

What is negative allosteric regulation ?

Answer 9

When the allosteric effector binds meaning the substrate can’t bind and reaction slows down
- the allosteric effector will be an inhibitor

Question 10

How do regulatory enzymes work ?

Answer 10

• enzymes have more than one allosteric site and several regulatory sites
• each site will selectively bind a ligand
• the conformational change of the active site will reflect the summation of signals

Question 11

Describe adenylate control

Answer 11

• ATP has high energy and is used for ion transport etc
• this will turn it into ADP and AMP which have low energy
• these are used as metabolic fuels to make ATP

Question 11

What is the role of adenylate kinase ?

Answer 11

turns ADP into ATP and AMP

Question 12

How are high levels of ATP maintained ?

Answer 12

Electron transport and oxidative phosphorylation maintain high levels of ATP compared to ADP and AMP
ATP > ADP&raquo_space; AMP

Question 13

What can energy charges range from ?

Answer 13

energy charges range from 0 which is all AMP to 1 which is all ATP

Question 14

What is the significance of energy charges ?

Answer 14

• ATP generating pathways are inhibited by a high energy charge
• ATP utilising pathways are stimulated by a high energy charge

Question 15

What happens when ATP levels are high ?

Answer 15

If ATP levels are high then ATP generating pathways are catabolic e.g. glycogenolysis and glycolysis

Question 16

What happens when ATP levels are low ?

Answer 16

If ATP levels are low then ATP generating pathways are anabolic e.g. gluconeogenesis and lipogenesis

Question 17

What is covalent modification ?

Answer 17

It is the modification of existing protein structure as it is a quicker process than changing the levels of enzyme

Question 18

What are the different types of covalent modification ?

Answer 18

• adenylation
• methylation
• phosphorylation (most common)

Question 19

What is the role of phosphatase ?

Answer 19

It will hydrolyse phosphate groups and remove them

Question 20

Which amino acids can be phosphorylated ?

Answer 20

• serine
• tyrosine
• thyronine
  because the hydroxyl side chains are replaced by phosphate groups

Question 21

What are the consequences of changing the conformation of a protein ?

Answer 21

• changes the Vmax or Km of the enzyme
• changes the sensitivity to the substrate
• changes the sensitivity to inhibitors or activators