3- enzymes

What are enzymes?

Biological catalysts which increase the rate of a chemical reaction.

How do enzymes act as biological catalysts?

They increase the rate of a chemical reaction by lowering the activation energy of the reactions they catalyse.

What type of reactions can enzymes work on?

Anabolic and catabolic and intracellular and extracellular reactions.

What is the active site?

The area of the enzyme where the complementary substrate binds.

Enzymes are specific to substrates they bind to, as only one type of substrate fits into the active site of the enzyme.

What happens during the induced fit model of enzyme action?

The enzyme and substrate form a complex, the structure of the enzyme is distorted so that the active site of the enzyme moulds around the substrate.

How can the initial rate of a reaction of a gradient on a concentration-time graph be calculated?

By drawing a tangent and measuring the gradient at t=0.

What factors affect the rate of enzyme-controlled reactions?

• Enzyme concentration

• Substrate concentration

• Temperature

Explain how the enzyme concentration affects the rate of enzyme-controlled reactions?

The rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to.

However, increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates so substrate concentration becomes the limiting factor.

Explain how the substrate concentration affects the rate of enzyme-controlled reactions?

As the concentration of substrate increases, the rate of reaction also increases as more enzyme-substrate complexes are formed.

However, beyond a certain point, the rate of reaction no longer increases as enzyme concentration becomes the limiting factor.

Explain how the temperature affects the rate of enzyme-controlled reactions?

The rate of reaction increases up to the optimum temperature which is the temperature each enzyme works best at.

However, the rate of reaction decreases beyond the optimum temperature because enzymes become denatured as hydrogen bonds are broken within the protein, changing the shape of the enzyme’s active site so it is no longer complementary to the substrate.

What are inhibitors?

Substances which stop the enzyme from binding to its substrate, therefore controlling the progress of a reaction.

It can be reversible or irreversible.

What are the two categories of inhibition?

• Competitive inhibition

• Non-competitive inhibition

How do competitive inhibitors work?

An inhibitor molecule competes with the substrate for binding to the active site of the enzyme, therefore preventing the substrate from binding.

It can be reversed by increasing the substrate concentration.

How do non-competitive inhibitors work?

An inhibitor binds to the allosteric site of the enzyme and changes the shape of the enzyme. This decreases the reaction rate as the active site doesn’t fit the substrate and the substrate cannot bind to the enzyme.

It cannot be reversed by increasing substrate concentration.

What is end-product inhibition or feedback inhibition?

When the end-product of a multi-step reaction may act as an inhibitor to the enzyme which catalyses the initial stage of the reaction.