Ocr As Biology - Enzyme Inhibition

Front 1

Enzyme activity can be inhibited. Name the two types of inhibition.

Back 1

Competitive and non-competitive.

Front 2

Explain how competitive inhibition works.

Back 2

• A competitive inhibitor have a similar shape to the substrate molecules.
• They compete with the substrate molecules to bind to the active site, but no reaction takes place.
• Instead they block the active site, so no actual substrates can bind.

Front 3

[competitive inhibition]

What are the effects of increasing inhibitor concentration?

What are the effects of increasing substrate concentration?

Back 3

• An increase in the inhibitor concentration means that more active sites on the enzyme will be used up, lowering the rate of reaction.
  
• An increase in the substrate concentration means that there is a higher chance of a substrate binding with an active site than an inhibitor. This increases the rate of reaction, up to a point.

Front 4

Explain how non-competitive inhibition works. Explain if they are competing with substrates. What effect would increasing the substrate concentration have?

Back 4

• Non-competitive inhibitors bind to enzymes away from their active sites, these sites are called allosteric sites.
• They cause the active site of the enzyme to change shape, which does not allow substrates to bind to it.
• They do not 'compete' with substrates as they are a different shape and bind to different areas.
• Increasing the substrate concentration wont make a difference to the rate of reaction - enzyme activity will still be inhibited.

Front 5

Inhibitors can be reversible or non-reversible. What factors determine this?

Back 5

• If the bond between the enzyme and inhibitor are strong, covalent bonds, the inhibitor cannot be removed easily and the inhibition is irreversible.
• If the bond between the enzyme and inhibitor are weaker hydrogen bonds or weak ionic bonds, the inhibitor can be removed and the inhibition is reversible.

Front 6

Some drugs and metabolic poisons are enzyme inhibitors.

Give two examples of medicinal drugs that are enzyme inhibitors.

Back 6

Medicinal drugs:

• Rerverse transcriptase inhibitors - an antiviral that inhibits the enzyme reverse transcriptase, which catalyses the replication of viral DNA. This stops the virus from replicating.
• Penicillin - inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall and prevents the cell from regulating osmotic pressure. This causes the cell to burst and the bacterium is killed.

Front 7

Some drugs and metabolic poisons are enzyme inhibitors.

Give three examples of metabolic poisons that are enzyme inhibitors.

Back 7

• Cyanide - an irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiration reactions. Cells that cant respire die.
• Malonate - inhibits succinate dehydrogenase which catalyses respiration reactions.
• Arsenic - inhibits the action of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions.

Front 8

What is a metabolic pathway?

Back 8

A metabolic pathway is a series of connected metabolic reactions. The product of the first reaction takes part in the second reaction and so on. Each reaction is catalysed by a different enzyme.

Front 9

What is product inhibition?

Back 9

When an enzyme is inhibited by the product of the reaction they catalyse.

Front 10

What is end-product inhibition?

Back 10

End-product inhibition is when the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway, breaking the chain and stopping the process.

Front 11

Is end-product inhibition reversible or irreversible?

Back 11

Reversible.

Front 12

Is product inhibition reversible or irreversible?

Back 12

Reversible.

Front 13

How is end-product inhibition a good way of regulation in the body? Give an example of end-product inhibition regulating in the body.

Back 13

• When too much of a substance (end-product) is made, that substance acts as an inhibitor to a previous enzyme that acts earlier in the pathway. This stops the end product from being produced.
• Product and end-product inhibition is reversible. So when the level of product starts to drop, the level of inhibition will also drop, causing the enzymes to function again and more product can be made. This is a constant cycle.
• An example of this is ATP inhibiting phosphofructokinase (phospho-fructo-kin-ase). Phosphofructokinase is enzyme involved in the metabolic pathway that breaks down glucose into ATP. A high level of ATP prevents more ATP from being created as it inhibits an enzyme that found earlier in the pathway.

Front 14

How can enzyme inhibition protect cells? Give an example.

Back 14

• Enzymes are sometimes synthesised as inactive precursors in metabolic pathways, to prevent them from causing damage to cells.
• For example, proteases (which break down proteins) are synthesised as inactive proteins to stop them damaging the cell that they are made in. Part of the precursor molecule inhibits action as an enzyme. Once this part is removed (via. a chemical reaction), the enzyme becomes active.