enzymes

Question 1

Induced fit theory

Answer 1

the enzyme shape changes to for the profile of the substrate i.e. it is flexible and can mould itself around the shape of the substrate causing strain on the substrate molecule distorts a particular bond and consequently lowers the A.E.

Question 2

Lock and key theory

Answer 2

Enzymes has an active site of a specific shape (1)the substrate that is complementary (1)binds to the active site (for a fraction of a second)(1)

Question 3

What happens when an enzyme is denatured

Answer 3

Heat about OPTIMUM breaks HYDROGEN BONDS (1)causing TERTIARY STRUCTURE to unfold (1)active site CHANGES SHAPE (1)substrate can no longer bind to ACTIVE SITE (1)fewer E-S COMPLEXES form

Question 4

how does pH adversely affect enzyme activity?

Answer 4

IONIC BONDS break in TERTIARY structure (1) active site changes shape, substrate can’t bind to ACTIVE SITE (1)charges on AMINO ACIDS in active site affected (1)fewer E-S COMPLEXES form

Question 5

Competitve inhibition

Answer 5

Inhibitor has a SIMILAR shape to substrate (1)Binds competitively to the active site (1)has a complementary shape (1)less E-S COMPLEXES form

Question 6

Non-competitve inhibition

Answer 6

Inhibitor binds somewhere other than the active site(1)causing conformational damage in the shape of the active site (1)substrate can no longer bind (1)less E-S COMPLEXES FORM

Question 7

How is starch digested in the body?

Answer 7

SALIVARY AMYLASE (1) breaks down STARCH to MALTOSE (1)MALTASE breaks down MALTOSE to GLUCOSE (1) by HYDROLYSIS (1) enzymes CATALYSE the breakdown of the GLYCOSIDIC bond (1)

Question 8

The enzyme tyrosine kinase (TK) is found in human cells. TK can exist in a non-functional and a functional form. The functional form of TK is only produced when a phosphate group is added to TK. Addition of a phosphate group to the non-functional form of TK leads to production of the functional form of TK.Explain how.

Answer 8

1. (Phosphate) changes shape of TK/changes shape of enzyme/changes the active site;2. Active site forms/becomes the right shape/can bind to substrate/complementary to substrate/E-S complex can form;

Question 9

Induced fit and lock and key are two models used to explain the action of enzymes. Describe the induced fit model of enzyme action.

Answer 9

Active site / enzyme not complementary; Active site changes (shape) / is flexible;(Change in enzyme allows) substrate to fit / E-S complex to form;

Question 10

Describe one way that the lock and key model is different from the induced fit model.

Answer 10

Active site does not change (shape) / is fixed (shape) / is rigid does not wrap around substrate / (already) fits the substrate / is complementary (before binding);

Question 11

Does the activation energy have to be higher or lower than the combined kinetic energy for a reaction to take place?lower

Answer 11

lower

Question 12

How do you lower the activation energy of reactions?

Answer 12

By adding enzymes to the reaction

Question 13

Define activation energy

Answer 13

The minimum amount of energy needed to get a reaction going.

Question 14

what is meant by the term turnover ?

Answer 14

the number of substrate molecules that can act upon a single molecule of the enzyme in one minute.

Question 15

Why is the induced fit hypothesis better than the lock and key mechanism?

Answer 15

The induced fit theory takes into account the change in shape with the active site of an enzyme

Question 16

Why is the activation energy low when enzymes catalyse a reaction?

Answer 16

Little energy is needed to bring the 2 substrate molecules together.

Question 17

explain why the rate of reaction is so slow below 10 degrees

Answer 17

Molecules have less kinetic energy so they move more slowly and are less likely to collide and react.

Question 18

What would the rate of reaction if some of the enzymes and substrates were frozen and then warmed to 40 degrees?

Answer 18

freezing does not denature the enzyme so the rate of reaction would be unaffected

Question 19

What happens to enzymes as the temperature rises beyond the optimum temperature?

Answer 19

The atoms wihin the enzymes gain kinetic energy and vibrate so rapidly that the weak bonds that maintain the tertiary structure break and he molecule can unravel causing the active site to change shape therefore denaturing the enzyme

Question 20

why do most enzymes denature in strongly acidic or alkaline solutions?

Answer 20

The H+ in an acid and the OH- in an alkaline are attracted to the charges on the amino acid they interact with them and disrupt the bonds that maintain the molecules 3D shape destroying the active site.

Question 21

what would increasing the concentration of enzymes or substrate do to the rate of reaction?

Answer 21

This would increase the rate of reaction up to a maximum when all the active sites are occupied.

Question 22

what do competitve inhibitors do?

Answer 22

Block the active site so the rate of reaction is slower.

Question 23

Do competitive inhibitors attach permenantly to the active site?

Answer 23

No and neither does it damage the enzyme

Question 24

what do non-competitve inhibitors do?

Answer 24

Change the shape of the active site and prevent substrate binding.

Question 25

Do inhbitors attach to the active site?

Answer 25

No but to a different part of the enzyme.

Question 26

Are the substrate and the non-competitve inhibitor the same shape?

Answer 26

No as it does not bind to the active site so does not need to be the same shape

Question 27

proteases breaks down protein molecules into amino acids- explain how proteases in washing powders help to remove protein stains such as blood or egg from clothes?

Answer 27

protein consists of large molecules and are not soluble in water proteases breaks down the protein into amino acids which is soluble in water and can therefore be washed away

Question 28

Hexosaminidase only breaks down gangliosides. It does not break down other lipids. Explain why this enzyme only breaks down gangliosides.

Answer 28

Active site has a(Complementary / specific) structure and shape whichonly fits / binds to gangliosides;Forms enzyme-substrate complexes;which means it cannot bind with other substances

Question 29

Methotrexate is a drug used in the treatment of cancer. It is a competitive inhibitor and affects the enzyme folate reductase.Explain how the drug lowers the rate of reaction controlled by folate reductase.

Answer 29

Methotrexate / drug is a similar shape / structure to substrate;Binds to / fits / is complementary to active site;Less substrate binds / less enzyme-substrate complexes formed;

Question 30

Methotrexate only affects the rate of the reaction controlled by folate reductase. Explain why this drug does not affect other enzymes.

Answer 30

Methotrexate / drug is only similar shape to specific substrate / only fits this active site;

Question 31

Induced fit and lock and key are two models used to explain the action of enzymes. Describe the induced fit model of enzyme action.

Answer 31

Active site / enzyme not complementary; Active site changes (shape) / is flexible;(Change in enzyme allows) substrate to fit / E-S complex to form;

Question 32

Describe one way that the lock and key model is different from the induced fit model

Answer 32

Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around substrate / (already) fits the substrate / is complementary (before binding)

Question 33

Aspirin is a very useful drug. One of its uses is to reduce fever and inflammation. Aspirin does this by preventing cells from producing substances called prostaglandins. Prostaglandins are produced byan enzyme-controlled pathway. Aspirin works by inhibiting one of the enzymes in this pathway. Aspirin attaches permanently to a chemical group on one of the monomers that make up the active siteof this enzyme.The enzyme that is involved in the pathway leading to the productionof prostaglandins is also involved in the pathway leading to theproduction of thromboxane. This is a substance that promotes blood clotting. A small daily dose of aspirin may reduce the risk ofmyocardial infarction (heart attack).Use information from the passage and your own knowledge to answer the following questions.Name the monomers that make up the active site of the enzyme

Answer 33

amino acids

Question 34

Aspirin is an enzyme inhibitor. Explain how aspirin prevents substrate molecules being converted to product molecules

Answer 34

1. Occupies/blocks/binds to active site2. Substrate will not fit / does not bind / no longer complementary to / enzyme-substrate complex not formed;