Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that act as biological catalysts

Question 2

What is the purpose of enzymes?

Answer 2

Increase the rate of reactions without being affected or use up

Question 3

Conditions of successful reactions with catalysts

Answer 3

1) Molecule, water and complementary enzyme must successfully collide to form a enzyme substrate complex
2) The free energy of the products must be less than the free energy of the substrates
3) Many reactions need a threshold amount of energy to start the reaction

Question 4

What is the activation energy?

Answer 4

The minimum energy required to start a reaction

Question 5

How do enzymes work?

Answer 5

They lower the activation energy by bending and stressing the bonds of the active site during the formation of enzyme substrate complexes . Allows reactions that happen at high temperatures to work at lower temperatures

Question 6

Catalysed reaction examples: Digestion

Answer 6

Large complex molecules broken down into small simple molecules before absorption and assimilation

Question 7

Enzyme structure

Answer 7

Proteins with specific tertiary structures which gives them a specific 3D shape

Question 8

What is the specific area of an enzyme key to its function?

Answer 8

The active site, the rest of the enzyme is to hold it in the correct shape via hydrogen, ionic and disulphide bonds

Question 9

What allows substrates and active sites to bind together?

Answer 9

Active sites have unique shapes complementary to only one substrate

Question 10

when an enzyme active site binds to a substrate…

Answer 10

the substrate is held in the active site due to temporary bonds formed between the substrate and amino acids in the active site. It is these bonds that bend and stress to lower activation energy

Question 11

What is the induced fit model?

Answer 11

That the active site is not fully fixed in shape and that the substrate induces a change in the active site making it more complimentary

Question 12

How is this change caused?

Answer 12

By the vending and stressing of bonds but once the substrate leaves the active site returns to its previous shape

Question 13

How to measure the rate of enzyme-controlled reactions

Answer 13

1)The formation of products
2) Disappearance or breakdown of the substrate

Question 14

Calculating the rate of reaction

Answer 14

Change in measurement/ Time taken

Finding the gradient of the line

Question 15

Factors affecting enzyme controlled reactions

Answer 15

•Temperature
•pH
•Substrate concentration
•Enzyme concentration

Question 16

Affecting the enzyme controlled reactions

Answer 16

Anything that’s alters the shape of the active site or the number of successful collisions will affect the number of enzyme substrate complexes formed and therefor the rate of reaction

Question 17

How does substrate and enzyme concentration affects the rate of reaction?

Answer 17

More enzyme substrate complexes will be formed

Question 18

How does the temperature affect the rate of reactions?

Answer 18

Every enzyme has an optimum so as the temp increases the enzyme and substrate has more kinetic energy, therefore move around more and are more likely to collide and form ESC

Question 19

What else does temperature rises cause?

Answer 19

Causes hydrogen and ionic bonds between the R groups break, changing the tertiary structure and the active site which is no longer complementary so fewer ESC formed. Enzyme denatures

Question 20

What does denaturation cause?

Answer 20

a permanent change in the tertiary structure. Once this change happens it will never work again

Question 21

What is the effect of pH on the rate of reaction?

Answer 21

The active site changes shape and the substrate will no longer be complementary. No ESC formed so rate of reaction decreases either side of the optimum

Question 22

What is pH?

Answer 22

A measure of hydrogen ion concentration

Question 23

pH calculated by?

Answer 23

-Log ^10 H+)

Question 24

Concentration values

Answer 24

A H+ conc of 10^-19 has a pH of 9, a conc of 10^-2 has a pH of 2. Small changes in pH is a large chnage is H+ concentration

Question 25

What happens with pH changes?

Answer 25

Change H+ can break the hydrogen and ionic bonds between -NH and the -C=O groups of the amino acids in the tertiary structures

Question 26

Effect of low substrate concentration

Answer 26

As substrate concentration increases, the rate of reaction increases then levels off. Initial rate is slow when concentration is low because not all active sites are saturated. Substrates is a limiting factor.

Question 27

Effect of high substrate concentration

Answer 27

As the substrate concentration increases, the active sites are filled and the rate of reaction increases due to more ESC forming. Substrates is no longer the limiting factor. When the rate of reaction levels off, there is a high concentration of substrate and no further increase in rate since enzymes can’t form anymore ESC as all active sites are filled/saturated. Concentration of enzyme is now the limiting factor

Question 28

Why do reactions plateaus?

Answer 28

Substrates have been used up so no more to react

Question 29

Effects of low enzyme concentration

Answer 29

As the enzyme concentration increases the rate of reaction increases and then levels off (fixed substrate concentration). Rate of reaction is low when there is a low enzyme concentration because all active sites of enzyme are saturated. Enzyme concentration is limiting factor

Question 30

Effect of high enzyme concentration

Answer 30

As the enzyme concentration increases, there are more active sites available for substrate to bind to so rate of reaction increases, due to more ESC forming. When rate of reaction levels off there is a high concentration of enzyme, there is no further increase in rate of reaction since enzyme cannot form ESC as there are more active sites than substrates

Question 31

What is an inhibitor?

Answer 31

Substances which decrease the rate of reactions

Question 32

Common inhibitors

Answer 32

Drugs that are enzyme inhibitors as they stop them from speeding up biochemical processes

Question 33

What are competitive inhibitors?

Answer 33

They have a similar shape to the substrate which bind to the active site of a specific enzyme and block the active site to prevent enzyme substrate complexes forming

Question 34

What happens to competitive inhibitors once they leave the active site?

Answer 34

As they are not permanently bound to the active site so when it leaves a substrate can bind

Question 35

Why do competitive inhibitors reduce the rate of reaction?

Answer 35

Fewer enzyme substrate complexes form so fewer products are formed. Some products stay formed because not all active sites are occupied by the inhibitors

Question 36

What are non-competitive inhibitors?

Answer 36

They change the shape of the active site so that it is no longer complementary to the substrate

Question 37

Where do non-competitive inhibitors bind to?

Answer 37

A site known as the allosteric site which is away from the active site

Question 38

Why do non-competitive inhibitors reduce the rate of reactions?

Answer 38

Fewer enzyme substrate complexes form so fewer products are formed as a result

Question 39

What type of inhibitor is similar to substrate?

Answer 39

Competitive

Question 40

What type of inhibitors is different to substrate shape?

Answer 40

Non-competitive

Question 41

Competitive inhibitor graphs

Answer 41

It is the difference between the number of inhibitor molecules and number of substrate molecules that dictate the inhibitors effect on the rate of reaction. Adding more substrate means there’s a higher probability the substrate will enter the active site compared to an inhibitor. Reaction will still be reduced but eventually all substrate will be broken down

Question 42

What does increasing substrate concentration do to competitive inhibitors?

Answer 42

It can overcome the competitive inhibitors

Question 43

Non-competitive inhibitor graphs

Answer 43

Changing the shape of the active site reduces the number of active sites available for substrates to bind to (It’s like lowering the enzyme concentration) so adding more substrates won’t speed up the rate of reaction and it is always lower than the rate of reaction with a competitive inhibitor

Question 44

What does increasing the substrate concentration do to non-competitive inhibitors?

Answer 44

It cannot overcome non-competitive inhibitors