Module 2: Enzymes

Question 1

What is an enzyme?

Answer 1

Tertiray globular protein that is a biological catalyst, which can speed up reactions by lowering activiation energy

Question 2

How do enzymes show specificity?

Answer 2

Have a specific shape so the substrate has a specific shape for the enzyme active site

Question 3

Define catabolism

Answer 3

Break down complex molecules into smaller ones, releasing energy in metabolic pathways

Question 4

Define anabolism

Answer 4

Build up molecules from simple ones - components synthesised and assembled into cells to form tissues, organs and whole organisms

Question 5

Define metabolism

Answer 5

Almost all reactions in living organisms are catalysed by enzymes

Question 6

Define intracellular enzymes. Give an example

Answer 6

Catalyse reactions in a metabolic pathway within cells e.g. catalase to break down hydrogen peroxide into oxygen and water to prevent accumulation and therefore poisoning of the body.

Question 7

Define extracellular enzymes. Give examples

Answer 7

Secreted from cells and used outside of cells e.g. trypsin (protease) catalyses the break down of proteins into small peptide chains, which can then be broken down into amino acids by other proteases. Prouced by the pancreas and released into the small intestines. The amino acids released are absorbed by the intestine lining.

Starch broken down partially into maltose by amylase - produced by salivary glands and pancreas - mouth and small intestines. Maltase breaks the maltose down into glucose in the small intestines.

Question 8

Why is the active site of an enzyme so important? What would happen is it changed shape?

Answer 8

Provides a complementary shape for the substrate molecule. Without the specific shape reactions would not take place, because the substrate would not fit into the active site, and so an ESC would not form, and no product would form

Question 9

Define activation energy

Answer 9

The energy needed for a reaction to start

Question 10

What do enzymes do to the activation energy? Why?

Answer 10

Lower activation energy providing an alternative route in order to increase the rate of reaction

Question 11

What is the lock and key mechanism?

Answer 11

The enzyme active site is complementary to the shape of the substrate, and the substrate fits into the active site perfectly, like a key has a specific shape to a lock - specificity. Temporary bonds form between the R-groups of the active site and the substrate

This forms and enzyme substrate complex where the substrate reacts and forms products in an enzyme product complex

Question 12

What is the induced-fit hypothesis?

Answer 12

The active site changes shape slightly when the substrate reacts with the enzyme. Means the binding is more effective. R-groups of amino acids give a precise conformation. Strain put on the substrate due to binding, weakening bonds in the substrate, lowering the activation energy

Question 13

What interaction occurs between the substrate and enzyme to help the reaction along?

Answer 13

R-groups of enzyme active site and substrate interact to form temporary bonds, which puts strain on the bonds within the substrate, helping the reaction along.

Question 14

What is the effect of temperature on an enzyme?

Answer 14

Slow reaction at low temps = molecules have low KE, so fewer collisions between enzyme and substrate
Higher temps = more collisions occur and with more KE to break bonds in the substrate. Optimum temp occurs here and product is formed quickly and efficiently
Highest temps = molecules vibrate too much breaking the H bonds within the enzyme - denaturation - changes specific 3D shape of active site so no longer complementary with substrate - tertiary structure altered

Question 15

What is the effect of pH on enzyme activity?

Answer 15

Change from optimum reduces rate of reaction
H ions interact with R groups of amino acids
Breaks H and ionic bonds at active site
pH very different from the optimum will denature enzyme changing the specific 3D shape of the enzyme active site - no longer complementary

Question 16

How can the pH of a reaction be maintained?

Answer 16

Use of a buffer

Question 17

How does subsrate concentration affect enzyme activity?

Answer 17

As substrate conc. increases initial rate of reaction increases - more substrate available to bind with active site
At high substrate conc. all enzyme active sites are occupied - more substrate added has no effect - enzyme working at Vmax - plateau in graph occurs

Question 18

How does enzyme conc. affect enzyme acivity?

Answer 18

Same as with substrate concentration - active sites available initially so increased rate of reaction - more product produced - directly proportional
All active sites full so Vmax reached and reaction graph plateaus as rate can no longer increase
Adding more substrate would increase rate of reaction again

Question 19

What is the temperature coefficient (Q10)?

Answer 19

Measure of how much the rate of reaction increases with a 10 degree increase in temperature

Question 20

What is the typical Q10 for enzyme controlled reactions?

Answer 20

2 - means rate doubles with every 10 degree increase

Question 21

Define cofactor

Answer 21

Non-protein molecule that is either part of the enzyme structure or forms a temporary association with it. Help ensure the reaction occurs at the same rate.

Question 22

Define prosthetic group

Answer 22

Non-protein groups or cofactors that are permanently bound to the enzyme

Question 23

Give an example of a prosthetic group

Answer 23

Zinc ions (Zn2+) form part of the structure of carbonic anhydrase - necessary for the metabolism of carbon dioxide

Question 24

Define coenzymes

Answer 24

Organic non-protein molecules that bind temporarily to the active site

Question 25

What happens to coenzymes during a reaction?

Answer 25

Chemically changed and need to be recycled to their original shape

Question 26

Give an example of coenzymes

Answer 26

Water soluble vitaminse.g. B3 used to synthesis NAD so H atoms can be transferred between molecules in respiration to form NADH

Question 27

Give an example of a cofactor

Answer 27

Chlorine (Cl-) helps form the correctly shaped active site in amylase for the breakdown of starch

Question 28

Describe competitive inhibition

Answer 28

The inhibitor has a similar shape to the substrate molecule and competes for the active site Inhibitor binds to an enzyme active site before a substrate molecule can This blocks the substrate from the active site The substrate is unable to bind with the active site so no ESC, and no product can form This reduces the rate of reaction

Question 29

How can the effects of competitive inhibtion be reversed?

Answer 29

Increasing substrate concentration

Question 30

Describe non-competitive inhibition

Answer 30

Inhibitor binds to another site in the enzyme called the allosteric site This distorts the shape of the active site so substrate is unable to bind to the active site The inhibitor may bind permanently or temporarily- determines whether reversible or not No ESC formed, so no product - decrease rate of reaction

Question 31

Give an example of a competitive inhibitor

Answer 31

Statins work against enzymes in the synthesis of cholesterol. This can reduce blood cholesterol conc. decreasing the risk of heart disease

Question 32

Give ans example of a non-competitive inhibitor

Answer 32

Organophosphates used in insecticides and herbicides inhibit acetyl cholinerterase - used for nerve impulses. Can lead to muscle cramps, paralysis and even death if ingested

Question 33

Define inactive precursor enzymes

Answer 33

Enzymes produced in an inactive form as they may cause damage in the place produced, and are only activated under certain conditions

Question 34

What has to happen to precursor enzymes?

Answer 34

A change in tertiary structure particularly the active site. Adding a cofactor allows this

Question 35

What is a precursor protein called before activation by a cofactor?

Answer 35

Apoenzyme

Question 36

What is a precursor enzyme activated by a cofactor called?

Answer 36

Holoenzyme

Question 37

What are proenzymes or zymogens?

Answer 37

Chacnegs in tertiray structure from another enzyme e.g. protease can change the conditions e.g. pH or temp. activating a precursor enzyme

Question 38

Describe end-product inhibition

Answer 38

As an enzyme converts substrate to product the rate of reaction is lowed down or inhibited The end product binds to an allosteric site Prevents further substrate binding As product levels fall the enzyme can become active again This can prevent too much product forming at once and only on demand - negative feedback