Biological Molecules: Many proteins are enzymes

Question 1

How do enzymes work to speed up a reaction?

Answer 1

They lower the activation energy required to start a reaction

Question 2

What determines the shape of an enzyme’s active site?

Answer 2

Its tertiary structure

Question 3

Explain the induced fit model:

Answer 3

• Enzyme’s active site and substrate have a similar shape but are not completely complementary
• When the substrate starts to bind, the active site changes shape to become complementary
• This puts stress on the substrates bonds making them easier to break, lowering the activation energy

Question 4

How does an increasing enzyme concentration impact the rate of reaction if there are excess substrates?

Answer 4

• Increase reaction (linear)
• There will be more active sites and sufficient substrates

Question 5

How does an increasing enzyme concentration impact the rate of reaction if there is limited substrates?

Answer 5

• Increase reaction partially then level off
• There will be more active sites (increase at the start)
• But then an insufficient amount of substrate (level off)

Question 6

How does an increasing substrate concentration impact the rate of reaction if there are excess enzymes?

Answer 6

• Increase reaction (linear)
• There will be more substrates and sufficient enzymes

Question 7

How does an increasing substrate concentration impact the rate of reaction if there are limited enzymes?

Answer 7

• Increase reaction partially then level off
• There will be more substrates (increase at the start)
• But then an insufficient amount of enzymes (level off)

Question 8

How do competitive inhibitors impact the rate of reaction if there are an increasing number of substrates?

Answer 8

• Initial decrease (Competitive inhibitor binds to enzyme and so prevents other substrate molecules from doing so)
• Maximum rate of reaction is reached (competitive inhibitors only temporarily bind to the enzyme)

Question 9

How do non-competitive inhibitors impact the rate of reaction if there are an increasing number of substrates?

Answer 9

• Decreases (maximum) rate of reaction

Question 10

How does temperature affect rate of reaction?

Answer 10

• Increase up to optimum temperature
• Rapid decrease after optimum temperature

Question 11

How do high temperatures after the optimum temperature slow down enzymes and the rate of reaction?

Answer 11

• Break hydrogen bonds
• Changes tertiary structure
• Changes active site
• Reduces frequency of enzyme-substrate complex forming

Question 12

How do changes in pH slow down enzymes and the rate of reaction?

Answer 12

• Breaks hydrogen and ionic bonds
• Changes tertiary structure
• Changes active site
• Reduces frequency of enzyme-substrate complex forming

Question 13

How do enzymes speed up the rate of chemical reactions?

Answer 13

Lower the activation energy needed for the reaction to start.

Question 14

Give the two reasons why forming an enzyme-substrate complex lowers the activation energy:

Answer 14

1) The enzyme will hold two substrate molecules together, reducing repulsion so they can bond more easily.
2) Enzymes put strain on the substrates bonds when catalysing, so the substrate breaks up more easily.

Question 15

What are the two enzyme models?

Answer 15

• Lock and key model
• Induced fit model

Question 16

Explain the process of the lock and key model:

Answer 16

• Enzyme and substrate fit like a ‘lock and key’
• Substrate and active site have a complementary shape

Question 17

Why is the lock and key model not a full explanation?

Answer 17

Evidence shows that the enzyme-substrate complex changes shape slightly to complete the fit.

Question 17

Explain the process of the induced fit model:

Answer 17

• Substrate binds to enzymes active site
• Enzymes active site changes slightly so enzyme-substrate complex is completed.

Question 18

Why are enzymes only able to catalyse one specific substrate?

Answer 18

Only one complementary substrate will fit into the active site.

Question 19

An enzymes active site is determined by its ________.

Answer 19

Tertiary structure

Question 20

An enzymes tertiary structure is determined by its _______.

Answer 20

Primary structure.

Question 21

What determines an enzymes primary structure?

Answer 21

Genes

Question 22

What are the two ways of measuring the rate of a reaction?

Answer 22

1) Measuring how fast a product is made.
2) Measuring how fast a substrate is broken down.

Question 23

How does pH affect rate of reaction?

Answer 23

• Increase up to optimum pH
• Rapid decrease after optimum pH

Question 24

What are enzyme inhibitors?

Answer 24

Molecules that bind to an enzyme and inhibit a reaction.

Question 25

Inhibition can either be _______ or ________.

Answer 25

Competitive or non-competitive.

Question 26

What do competitive inhibitors do?

Answer 26

Compete with substrate molecules to bind to the enzymes active site.

Question 27

Competitive inhibitors have a _______ shape to that of substrate molecules.

Answer 27

Similar

Question 28

When competitive inhibitors bind to an enzyme, a reaction ____ take place.

Answer 28

Doesn’t

Question 29

What do non-competitive inhibitors do?

Answer 29

Bind to the enzyme away from its active site, causing the active site to change shape so its complementary substrate can no longer fit.

Question 30

What are the two types of enzyme inhibitors?

Answer 30

Competitive
Non-competitive