Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts which are globular proteins, that can be used to break down or built up substrates.

Question 2

Describe the relationship between the enzyme and the substrate

Answer 2

They have a complimentary active site, which creates a enzyme-substrate complex.

Question 3

What are anabolic reactions?

Answer 3

Building up reaction (synthesis)

Question 4

What is a catabolic reaction?

Answer 4

Breaking down reaction (digestion)

Question 5

How do enzymes speed up reactions?

Answer 5

It lowers the activation energy

Question 6

What factors affect the rate of reaction?

Answer 6

• Concentration of enzymes
• Temperature
• pH

Question 7

When do catalysts work best?

Answer 7

In a high concentration at optimum temperature and at optimum pH.

Question 8

What different types of enzymes are there?

Give examples

Answer 8

• Extracellular enzymes
  (lipase, carbohydrase, protease, amylase, maltase)
• Intracellular enzymes
  (catalase)

Question 9

Where are enzymes found?

Answer 9

Mouth
Pancreas
Stomach
Salivary glands

Question 10

What is the function of enzymes?

Answer 10

Digestion and synthesis

Question 11

Where can enzymes be found?

Answer 11

Mouth, small intestines, stomach

Question 12

Where are enzymes produced?

Answer 12

Salivary glands, pancreas

Question 13

How do enzymes catalyse reactions?

Answer 13

Lower the activation energy

Question 14

What are inhibitors?

Answer 14

Molecules that prevent enzymes from carrying out their normal function

Question 15

Describe competitive inhibition

Answer 15

• Molecules that have a similar shape to the substrate of an enzyme can fit into the active site.
• This blocks the substrate from entering the active site, preventing the enzymes from catalysing the reaction.
• The enzyme can’t carry out its function and is ‘inhibited’
• By reducing the number of available active sites, the reaction is slowed.

Question 16

What are the three types of enzyme inhibitors?

Answer 16

• Competitive inhibition
• Non-competitive inhibition
• End-product inhibition

Question 17

What is the effect of a competitive inhibitor on rate of reaction?

Answer 17

It slows the rate of reaction, however it doesn’t change the v-max of the enzyme

Question 18

What are examples of competitive inhibitors?

Answer 18

• Statins are competitive inhibitors of an enzyme used in the synthesis of cholesterol
• Aspirin irreversibly inhibits the active site of COX enzymes, preventing the synthesis of prostaglandin particles and thromboxane, the chemicals responsible for producing pain and fever.

Question 19

What is a non-competitive inhibitor?

Answer 19

The inhibitor binds to the enzyme at a location other than the active site.

• This alternative site is called an “allosteric site”
• The binding of the inhibitor causes the tertiary structure of the enzyme to change, meaning the active site changes shape.
• The active site is no longer a complimentary shape to the substrate so it is unable to bind to the enzyme.
• The enzyme can’t carry out its function and it is said to be inhibited.

Question 20

Does a non-competitive inhibitor compete for an active site?

Answer 20

No, it binds to an allosteric site

Question 21

What is the effect of a non-competitive inhibitor on the rate of reaction?

Answer 21

Increasing the concentration of enzyme or substrate will not overcome the effect of a non-competitive inhibitor.

Question 22

Are non-competitive inhibitors permanently bound?

Answer 22

No, some may be irreversible

However, Proton pump inhibitors (PPIs) are used to treat long-term indigestion. They irreversibly block an enzyme system responsible for secreting hydrogen ions into the stomach.

Question 23

What is end-product inhibition?

Answer 23

It is a term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it. This acts as a negative-feedback control mechanism for the reaction.

Question 24

What is end-product inhibition an example of?

Answer 24

Non-competitive reversible inhibition

Question 25

What is a cofactor?

Answer 25

“Helper molecule”

They are non-protein molecules that need to be present to ensure that an enzyme-controlled reaction can take place.

Question 26

What is an Apoenzyme?

Answer 26

An enzyme that requires a cofactor but don’t have one

Question 27

What is a Holoenzyme?

Answer 27

An enzyme that requires a cofactor and is in possession of one.

Question 28

What are prosthetic groups?

Answer 28

Prosthetic groups are cofactors - required by certain enzymes to carry out their catalytic function.
- they are tightly bound and a permanent feature of the protein.

Question 29

What is an example of a prosthetic group?

Answer 29

Zinc ions (Zn2+) form an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.

Question 30

What is the difference between cofactors and coenzymes?

Answer 30

These helper molecules are components called cofactors. However, if the cofactor is an organic molecule, it is called a coenzyme.

Question 31

How do we obtain inorganic ion cofactors?

Answer 31

Via the diet as minerals, including iron, calcium, chloride and zinc ions.

Question 32

What is an example of inorganic ion cofactors?

Answer 32

The enzyme amylase, which catalysed the breakdown of starch, contains a chloride ion that is necessary for the formation of a correctly shaped active site.

Question 33

Where are coenzymes derived from?

Answer 33

Vitamins, a class of organic molecules found in the diet.

E.g. vitamin B3 is used to synthesise NAP (nicotinamide adenine dinucleotide), a coenzyme responsible for the transfer of hydrogen atoms between molecules involved in respiration. Coenzymes also bind temporarily to the active site. They are also usually changed by the reaction.

Question 34

What is an inactive precursor enzyme?

Answer 34

An enzyme that isn’t active, due to the lack of a cofactor. It is therefore known as a Apoenzyme, however after activation by a cofactor, it is then known as a Holoenzyme.