Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that speed up the rate of reaction. They catalyse at cellular cells (e.g respiration) and for the organism as a whole (digestion in mammals) but are not used up.

Question 2

How can enzymes affect the structure in an organism?

Answer 2

They’re involved in the production of collagen

Question 3

How can enzymes affect the functions of organisms?

Answer 3

Through processes e.g respiration and photosynthesis

Question 4

What is the definition of metabolism?

Answer 4

The total sum of chemical reactions which can be described as enzyme driven, this includes:

• respiration
• protein synthesis
• digestion
• photosynthesis
• DNA replication

Question 5

Why must enzymes be in an aqueous environment?

Answer 5

It allows both the enzyme and the substrate the ability to move and therefore collide with one another allowing for enzyme-substrate complexes

Question 6

What does it mean if an enzyme action is intracellular?

Provide an example

Answer 6

-made and retained inside the cell
Example of this include: -catalase enzyme breaks down hydrogen peroxide into harmless oxygen and water so that cells aren’t killed

Question 7

What does it mean if an enzyme action is extracellular?

Provide an example

Answer 7

-carries out function outside the cell
An example includes: -amylase works outside the cells in saliva to catalyse the hydrolysis of starch
-Trypsin is produced by pancreatic cells and released into the small intestine

Question 8

What is the structure of an enzyme?

Answer 8

• Globular protein: has a 3D, almost spherical shape + water soluble due to positioning of hydrophilic R group
• Has an active site: which has a very specific shape where the complementary substrate binds to

Question 9

Describe and explain the lock and key model as a mechanism of enzyme action

Answer 9

-lock and key suggests that the substrate fits perfectly into the active site as they have a specific and complementary shape to one another. When the substrate bonds to the active site, and enzyme substrate complex is formed. The products of the reaction are then released and it is now an enzyme-product complex. The enzyme is now free to bind with another substrate molecule.

Question 10

Describe and explain the induced fit model as a mechanism of enzyme action

Answer 10

(This is the new model)
The active site on the enzyme is initially not the correct shape in which to fit the substrate. As the substrate approaches the active site, the site changes and results in being the perfect fit, forming an enzyme substrate complex. After the reaction has taken place and the products have been released (enzyme-product complex) the active site returns to its normal shape.

Question 11

What effect does an increase in temperature (from 10 to 30 c) have on the rate of a reaction?

Answer 11

Kinetic energy is increased which increases the number of successful collisions, therefore more enzyme-substrate complexes are formed and the rate of reaction increases

Question 12

What is meant by optimum temperature?

Answer 12

When enzyme activity is at its highest

Question 13

What happens when the temperature is raised too high (40 to 60 c) on the rate of a reaction?

Answer 13

The increase of energy means vibrations are produced which break the bonds that hold the enzyme together. This means the enzyme denatures, meaning there is now an irreversible change to the shape of the active site, and so enzyme activity and rate of reaction decreases

Question 14

What does the temperature coefficient show in a reaction?

Answer 14

It shows how much the rate of the reaction changes when the temperature is raised by 10 degrees

Question 15

What is the formula for the temperature coefficient?

Answer 15

Q10 = rate at higher temperature / rate at lower temperature

Question 16

What is meant by optimum pH?

Answer 16

The pH the enzyme works best at

Question 17

What happens as you move away from the optimum pH on a graph?

Answer 17

The enzyme begins to denature (the H+ and OH- ions found in acids and alkalis break the ionic and hydrogen bonds that hold the enzymes tertiary structure together, resulting in it changing shape. Therefore enzyme activity decreases.

Question 18

Explain the effect of having few substrate molecules on rate of reaction.

Answer 18

Few substrate molecules mean there are many active sites free and able to be reacted, and so an increase in substrate concentration will increase the rate of reaction

Question 19

Explain the effect of having more substrate molecules on rate of reaction.

Answer 19

When there are more substrate molecules, all the active sites are engaged in catalysts. This therefore produces the maximum rate of reaction

Question 20

Explain the effect of having an excess of substrate molecules on rate of reaction.

Answer 20

An excess of substrate molecules means all active sites are engaged in catalysis and so an increase in substrate concentration will not change the rate of reaction

Question 21

What is an inhibitor?

Answer 21

A substance which slows the rate of reaction down on an enzyme- controlled reaction

Question 22

What is a competitive inhibitor?

Answer 22

A molecule which has a similar shape to the substrate of an enzyme, allowing for it to bind to the active site and block it and therefore stop the reaction. This is called an enzyme-inhibitor complex

Question 23

What is a non-competitive inhibitor?

Answer 23

An inhibitor which binds to another site on the enzyme called the allosteric site. This still causes the active site to change shape so that the substrate molecule can no longer fit, but it does not compete with the substrate.

Question 24

What is end product inhibition?

Answer 24

• A process whereby the final end product in a metabolic pathway acts as a regulator.
• when the amount of end product is high, it binds non-competitively to an enzyme in the pathway, blocking further production of itself.
• When the amount of end product fails, inhibition ends and the pathway restarts

Question 25

Why are some medical drugs classed as enzyme inhibitors?

Answer 25

• An antiviral drug uses a reverse transcriptase inhibitor to prevent viral DNA from replicating
• penicillin inhibits transpeptidase which forms the protein to synthesis bacterial cell walls

Question 26

What does a metabolic poison does and give an example of an inhibitor involved in respiration?

Answer 26

• they interfere with metabolic reactions in cells

- an example is cyanide which is a non competitive inhibitor of cytochrome C oxidase

Question 27

What is an organic cofactor (coenzyme) and what is it’s purpose?

Answer 27

• an organic, non-protein molecule which binds to certain enzyme in order to make them work
• the presence of cofactors may help the formation of the enzyme substrate complex (e.g certain ions)
• some cofactors change the charge distribution on the surface of the substrate or enzyme. This makes the temporary bonds in the enzyme substrate complex easier to form
• they may act as carriers moving chemical groups between enzymes
• an example are vitamins
  -e.g chloride ions are cofactors for the enzyme amylase

Question 28

What are prosthetic groups?

Answer 28

• the name given to a cofactor when it’s tightly bound to an enzyme
• they’re a permanent part of the enzymes active site and contribute to the final 3D shape and other properties of proteins e.g charge
  -e.g zinc ions are the prosthetic group for carbonic anhydrase

Question 29

Why are some enzymes released in an inactive form?

Answer 29

the active enzyme could cause damage to the cells producing them or the tissues where they are released + allows the location and conditions where the enzyme is active to be tightly regulated