Enzymes

Question 1

What type of molecule are enzymes?

Answer 1

Globular proteins

Question 2

What do enzymes act as?

Answer 2

Catalysts

Question 3

What do enzymes do and how do they do it?

Answer 3

Speed up reactions by lowering activation energy

Question 4

What shape do enzymes have and why do they have it?

Answer 4

Specific 3D shape due to the sequence of amino acids in the primary structure

Question 5

What specific region is functional in in an enzyme?

Answer 5

Active site

Question 6

What is the molecule called that an enzyme can act on?

Answer 6

Substrate molecule

Question 7

What do the enzyme and substrate fit together to form?

Answer 7

Enzyme substrate complexes

Question 8

What model explains enzyme action?

Answer 8

Induced fit

Question 9

What are the the 5 main stages of induced fit?

Answer 9

1. Active site forms as the enzyme and substrate interact
2. The proximity of the substrate leads to a change in the enzyme which forms the functional active site
3. The enzyme is flexible and moulds itself around the substrate and its general shape alters in the presence of a substrate
4. As it changes shape it puts strain on the substrate molecule which distorts bonds in the substrate to lower the activation energy needed to break the bond
5. Colliding with a substrate is a change in the enzymes environment and so its shape changes due to induced fit.

Question 10

What are the two ways to measure enzyme catalysed reactions?

Answer 10

1. Formation of products of the reaction

2. Disappearance of the substrate

Question 11

Why is the initial rate of reaction on a product time graph so quick?

Answer 11

Lots of substrate and no product at first so the enzyme and substrate molecules randomly collide and the substrate molecules easily bind to empty active sites and make many successful collisions forming many enzyme substrate complexes. The active sites are filled and substrate is broken down into products.

Question 12

Why does the product time graph begin to curve/ level off and get slower then stop?

Answer 12

Substrate decreases and product increases so it is more difficult for substrate molecules to bind as there are fewer substrate molecules and product gets int he way. It takes longer for the substrate to be broken down so rate of formation slows. Then all substrate is used up no new product can be formed.

Question 13

How do you measure rate of change from a curve on a graph?

Answer 13

Draw a tangent and work out the gradient.

Question 14

How do you work out the gradient?

Answer 14

Rise divided by run

Question 15

How do you find the rate of reaction?

Answer 15

1 divided by time.

Question 16

Why does temperature initially increase the rate of reaction?

Answer 16

More kinetic energy and vibrations so more successful collisions between the enzyme and substrate molecules which increases the number of enzyme substrate complexes.

Question 17

Why is the rate of reaction the highest at the optimum temperature for the enzyme?

Answer 17

Maximum amount of kinetic energy so maximum number of successful collisions and max amount of enzyme substrate complexes are formed

Question 18

Why does the rate of reaction decrease after the enzymes optimum temperature?

Answer 18

Decrease in kinetic energy so the number of successful collisions decreases as well as the number of enzyme substrate complexes. The hydrogen bonds break which denatures the protein so the active site changes shape and the reaction slows and stops.

Question 19

What is the effect of small changes in ph on an enzyme?

Answer 19

Small reversible changes causing inactivation

Question 20

What effect do extreme changes in ph have on an enzyme?

Answer 20

Permanent reversible changes as the hydrogen and ionic bonds are broken which denatures the protein so the active site changes shape and the substrate is no longer complementary.

Question 21

Why is the intial rate of reaction quick when you increase the substrate concentration?

Answer 21

More substrate is available so there is a greater chance of successful collisions so more enzyme substrate complexes are formed. When it reaches the max rate of reaction all the active sites are filled.

Question 22

Why does the effect of substrate concentration graph level off? And what is the point called where it begins to level off? How do you make it go up again?

Answer 22

The point of saturation there is excess substrate and not enough enzyme so the substrate concentration has no effect. To make it go up again add more enzyme.

Question 23

Why does enzyme concentration increasing initially increase the rate if reaction?

Answer 23

Increased number of enzymes proportionally increases rate of reaction as more enzyme substrate complexes are formed.

Question 24

Why does the enzyme concentration graph level off? How do you increase it again?

Answer 24

If the substrate is already being used as rapidly as it can be by the enzyme molecules or if the enzyme is in excess it wont continue to increase. To increase it again add more substrate.

Question 25

What shape are competitive inhibitors?

Answer 25

Similar molecular shape to the substrate

Question 26

What do competitive inhibition do?

Answer 26

Bind to active sites

Question 27

If substrate concentration increases what happens to the effect of the competitive inhibitor?

Answer 27

Decreases

Question 28

What happens when a competitive inhibitor leaves an active site?

Answer 28

Another molecule can take its place

Question 29

If the competitive inhibitor has a greater concentration will it take longer or shorter for all the substrate molecules to fill the active sites?

Answer 29

Longer

Question 30

Where do non competitive inhibitors bind to?

Answer 30

A binding site that is not the active site

Question 31

What do non competitive inhibitors do to active sites and what does that mean for substrate molecules?

Answer 31

Alter the shape of the active site so substrate molecules can no longer occupy them

Question 32

What effect does increased substrate concentration have on a non competitive inhibitor? Is the max rate of reaction ever reached?

Answer 32

No effect and the max rate of reaction is never reached.