ENZYMES II

Question 1

how to control metabolic reaction?

Answer 1

1 ) cells regulate their chemical reaction through the use of enzymes
2 ) cells couple link reactions tgt, driving energy -requiring endergonic reaction with the energy released by exergonic reaction
3 ) cells synthesize energy-carrier molecules like ATP that capture energy from exergonic reactions and transport them to endergonic reactions

Question 2

what are the five ways to control enzyme activity?

Answer 2

• regulation of the rate of enzymes synthesis and degradation
• proteolytic activation
• feedback inhibition
• non-covalent allosteric modulation
• covalent modification

Question 3

what is regulation of the rate of enzymes synthesis and degradation?

Answer 3

level of induction/repression of the gene encoding the enzymes and the rate of degradation of the mRNA produced from that gene affects rate of synthesis

Question 4

what is proteolytic activation?

Answer 4

• cell may synthesize an enzyme in an inactive form and activate it only when needed
• several enzymes are synthesized as larger inactive precursor forms called proenzymes or zymogens in which activation of zymogens involves irreversible hydrolysis of one or more peptide bonds

Question 5

what is feedback inhibition?

Answer 5

• activity of enzyme is inhibited by its product or by subsequent product produced further along the pathway hence preventing the buildup of intermediates and unnecessary use of metabolites and energy
• rate of reactions can be altered by effectors (inhibitors/activators)
• end product in branched metabolic pathways will bind to the enzyme at the control point (allosteric enzymes)

Question 6

what is non-covalent modulation?

Answer 6

• binding to an effector molecule to a regulatory/allosteric site of an allosteric enzymes will induce a conformational change in the enzyme, altering the affinity of the active site for the substrate
• modulation can be activation or inhibition

Question 7

what is covalent modification?

Answer 7

activity of many enzymes is altered by the reversible making and breaking of a covalent bond between the enzymes and a small non-protein group
- phosphorylation is catalysed by protein kinases whereas dephosphorylation is catalysed by protein phosphatase

Question 8

what is Vo , Km and Vmax?

Answer 8

Vo : initial velocity
Vmax : maximum velocity
Km : conc. of substrate needed for half Vmax

Question 9

how do you derive Vo?

Answer 9

[Vmax][S]/[Km+S]

Question 10

how do you drive Km?

Answer 10

[K2+K3]/[K1]

Question 11

what is irreversible enzyme inhibition?

Answer 11

inhibitors which bind irreversibly to an enzyme often form a covalent bond to an amino acid residue at/near the active site and permanently inactive the enzyme

Question 12

what is reversible enzyme inhibition?

Answer 12

1 ) Competitive inhibition
- competes with the substrate molecules to bind to the active site of the enzyme
- Km increase while Vmax remains unchanged
2 ) Non-competitive inhibition
- can bind to either E or ES complex
- bind reversibly at a site other than the active site and causes a change in the overall 3D conformation of the enzyme leading to a decrease in catalytic activity
- Km unchanged and Vmax decrease
3 ) Uncompetitive inhibition
- binds only to ES complex
- Km and Vmax both decrease