principles of science

Define the term substrate.

A molecule that gets acted upon by an enzyme.

Define the term product.

A molecule that is the result of a reaction.

Define the term reaction rate.

How fast a reaction occurs in terms of how much product is produced within a given time.

Define the term equilibrium constant.

A value that describe the ratio of products to reactants in a reversible reaction at equilibrium.

Define the term rate constant.

A value that describe the rate of a reaction.

Define the term activation energy.

The amount of energy required for molecules to have before they can react with each other.

Define the term induced fit.

This describes the model of enzyme action by which an enzyme has a complementary active site that is roughly the correct shape. When the enzyme joins with the substrate, the active site changes shape to fully fit the substrate, like a glove changing shape to fit a hand.

How does an enzyme assist reactions?

Enzymes stabilise the transition state, lowering its free energy and therefore lowering the activation energy of the whole reaction.

It does this in multiple ways:

• Proximity: by bringing substrates close enough together that they can react

• Orientation: orients substrates so they are in the best position to achieve transition state.

• Microenvironment: water molecules may inhibit reactions so the enzymes can provide a non-aqueous pocket for reactions to occur.

Describe the induced fit model of enzyme action.

• An enzyme has a specific tertiary structure, bringing amino acid residues close together to form the active site.

• The optimal conformation of the binding site is one that best complements the transition state of the reactants.

Describe cofactors and their purpose.

• Cofactors are non-protein compounds that bind with an enzyme in order for the enzyme to work.

• A whole enzyme (inc. cofactor) is called a holoenzyme. Without the cofactor, it is an apoenzyme.

• Cofactors can be prosthetic groups that bind tightly to the enzyme and are not modified during the reaction, or coenzymes (co-substrates), that bind loosely and reversibly and are modified during the reaction.

• Cofactors can be metal ions or organic molecules like vitamins.

• Many will bind near the active site to help facilitate the binding of the substrate.

Discuss Michaelis-Menten kinetics.

• This is the kinetics of a reaction where a substrate combines reversibly with an enzyme to form an enzyme-substrate complex, which then reacts irreversibly to form a product and regenerate the enzyme.

• This is represented by a hyperbolic graph of substrate concentration against rate of reaction.

• Reaction rate increases with substrate concentration, but then plateaus as all enzymes become saturated.

How is enzyme activity regulated?

• Temperature and pH:

  • As temperature increases, so does enzyme activity and therefore reaction rate. However, past the optimum temperature, the active site denatures and enzyme activity decreases and eventually stops.

  • As pH increases,