Enzymes

Question 0

What is the function of the active site?

Answer 0

Small part of the enzyme to which the substrate will bind i.e. it is the site of the chemical reaction

Question 1

List 6 features of enzymes

Answer 1

Highly specific, remain unaltered at the end of the reaction, don’t affect equilibrium, increase rate (or velocity) of reactions, all enzymes are proteins (very few RNA ones which aren’t) and they may require cofactors e.g. Zn

Question 2

Why are most active sites clefts or crevices?

Answer 2

This conformation allows exclusion of water thus it doesn’t interfere with the reaction. For reactions which require water this is obviously different.

Question 3

Briefly explain the two models of enzymatic reactions

Answer 3

Lock and key - enzyme is lock and substrate is key Induced fit hypothesis - binding of the substrate to the enzyme changes conformation slightly

Question 4

What do the y intercept, x intercept and gradient of the slope tell you on a Lineweaver-Burk plot?

Answer 4

X intercept - -1/Km Y intercept - 1/Vmax Slope - Km/Vmax

Question 5

Name the two main forms of enzyme regulation

Answer 5

Substrate/product concentration Changes in enzyme conformation

Question 6

What shape is the V vs [S] graph for allosterically controlled enzymes?

Answer 6

Sigmoidal - caused by positive co-operativity

Question 7

What is the most important type of modification for regulation?

Answer 7

Phosphorylation - P groups are added to hydroxyl groups on serine, threonine or tyrosine.

Question 8

What do kinases do?

Answer 8

Catalyse the reaction of attachment of phosphate groups

Question 9

What do proteases do?

Answer 9

Catalyse the removal of phosphate groups

Question 10

How are zymogens activated?

Answer 10

Removal of part of the polypeptide chain - many proteases are produce like this

Question 11

What do endogenous inhibitors do?

Answer 11

Regulate protease activity e.g. pancreatic trypsin inhibitor binds trypsin and stops activity

Question 12

What is the function of trypsin?

Answer 12

Activating pancreatic proteases. It’s the ‘master’ regulator

Question 14

How is the rate of enzyme synthesis usually regulated?

Answer 14

By increasing or decreasing the rate of transcription of mRNA

Question 15

List the major regulatory mechanisms that control enzyme activity

Answer 15

Allosteric, substrate and product concentration, covalent, proteolytic and altering amount of enzyme

Question 16

Give some examples of zymogens

Answer 16

Stomach - pepsinogen - pepsin Pancreas - trypsinogen - trypsin Pancreas - proelastase - elastase

Question 17

When is the intrinsic pathway for blood clotting activated?

Answer 17

Damaged membrane of blood cells promotes binding of factor XI

Question 18

When is the extrinsic pathway for blood clotting activated?

Answer 18

Trauma releases tissue factor (factor III)

Question 19

Draw out the blood clotting cascade

Answer 19

Question 20

What mechanisms are used in regulation of clot formation and breakdown?

Answer 20

Concentration of zymogens, digestion by proteases, specific inhibitors, fibrinolysis

Question 21

Briefly describe the steps in blood clotting

Answer 21

Inactive zymogens present at low concentration, amplification of initial signal, localisation of clotting factors, feedback activation by thrombin and termination of clotting

Question 22

Which way would an activator shift a graph of V vs [S]?

Answer 22

Left

Question 23

Which way would an inhibitor shift a graph of V vs [S]?

Answer 23

Right

Question 24

What is haemophilia caused by?

Answer 24

A defect in factor VII