Enzymes and Metabolism

Question 1

What is a catalyst

Answer 1

A chemical which speeds up the rate of a chemical reaction, remains unaltered by the reaction and lowers the activation energy

Question 2

What catalyst breaks down hydrogen peroxide

Answer 2

Manganese dioxide breaks down hydrogen peroxide into water and oxygen

Question 3

What are 4 properties of enzymes

Answer 3

They are biological catalysts, they are found in all living cells, they are proteins and they are said to be specific

Question 4

What is lock and key theory

Answer 4

The shape of an enzymes active site in complmentery (matches) to the shape of a molecule of its substrate.

Question 5

Explain the induced fit model

Answer 5

The active site of an enzyme is not a rigid structure, it is flexible and dynamic.

Question 6

What is an induced fit

Answer 6

-A induced fit occurs when the active site changes shape to better fir the substrate after the substrate binds.
-The substrate molecule(s) have a high affinity for the active site while the subsequent products have a low affinity allowing them to leave the active site.
-The induced fit of the active site lowers the activation energy, increasing the chance of the reaction being successful.

Question 7

Give an account of enzyme activity under the heading of induced fit

Answer 7

• The substrate binds to the active site of the enzyme.
• The shape of tyhe active site is complimentary to the shape of the substrate.
• The active site changes shape to better fit the substrate after it binds.
  -The induced fit of the active site lowers the activation energy, increasing the chance of the reaction being successful.
  -Substrates have a high affinity for the active site so are attracted to the ezymes. Products have a low affinity for the active site so are released from the enzyme.

Question 8

What factors affect enzyme activity

Answer 8

1) Temperature
2) Ph
3) Substrate concentration
4) Inhibitors

Question 9

How does temperature affect enzyme activity

Answer 9

Enzymes work faster as temperature increases.
The temperature enzymes work best at is called the OPTIMUM temperature.
The OPTIMUM temperature for most animal enzymes is 37°C.
After the optimum temperature the enzyme DENATURES (this means the enzymes active site has changed shape).

Question 10

What are metabolic pathways

Answer 10

Metabolism is the collective term for the many integrated and controlled pathways of enzyme catalysed reactions within a cell.

Metabolic pathways normally consist of several stages which are each regulated by specific enzymes
-the pathway can have reversible, irreversable and alternative steps,

Question 11

What catagories can metabolic pathways fall into

Answer 11

Anabolic reactions (synthesis) - Builds up large molecules from small molecules and requires energy.

Catabolic reactions (degredation) - breaks down larger molecules in smaller molecules and releases energy.

Question 12

Explain why altered genetic code fails to produce an enzyme

Answer 12

The protein/enzyme contains different amino acid(s)

Question 13

What three mechanisms can control metabolic pathways

Answer 13

Competitive inhibition, non-competitive inhibition and feedback/end product inhibition.

Question 14

What controls metabolic pathways

Answer 14

-Metabolic pathways are controlled by the prescence or abscene of particular enzymes and the regulation of the rate of reaction of key enzymes
-Control of these pathways is brought about by controlling enzymes action by feedback inhibition.
-Feedback inhibition occurs when the end-product in the metabolic pathway reaches a critical concentration.
-The end-product then inhibits an earlier ezyme, blocking the pathway (usually the first enzyme in pathway)
-This prevents further synthesis of the end-product and also prevents wasteful conversions.

Question 15

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Describe the effect of pH on an enzyme

Answer 15

-Each enzyme has a working range. Outside this range the enzyme is inactive.
-An enzyme has an optimum pH (enzyme is most active here)
-Either side of the optimum pH the enzyme does not work so well.

Question 16

Describe the effect of substrate concentration on enzyme action

Answer 16

-At low substrate concentration the reaction rate is low since there are too few substrate molecules to make maximum use of all active sites.
-Increasing substrate concentration increases reaction rate as more and more active site become involved
-Reaction rate levels off as there is further increase in substrate concentration since all active site have become involved (enzyme is saturated)

Question 17

What do inhibitors do and what are the two types

Answer 17

Inhibitors act by slowing down/ stopping the rate at which an enzyme controlled reaction can work.
The two types are competitive and non-competitive

Question 18

How do competitive inhibtors work

Answer 18

Competitive inhibitors bind at the active site, preventing substrates from binding. This effect can be overcome by increasing substrate concentration as it is less likely that the competitive inhibitor will be able to bind to an actove site instead of a substrate molecule.

Question 19

How do non-competitive inhibitors work

Answer 19

Non-competitive inhibitors bind away from the active site (allosteric site) to change the shape of the actie site (conformational change) to prevent the substrate from bidning. Non-competitive inhibitors can not be ovecome by increasing substrate concentraion as they do not compete for the enzymes active site.