Many proteins are enzymes Flashcards – AQA A-Level Biology - (7402)

What are enzymes, and what are most made of?

Enzymes are biological catalysts; most are proteins.

How does an enzyme increase the rate of a reaction?

It lowers the reaction’s activation energy.

What happens to an enzyme as it catalyses a reaction?

It is not consumed.

Where do enzymes catalyse reactions in organisms?

Both inside cells and outside cells. These reactions contribute to structures and functions from cells to whole organisms.

What determines the shape and chemical properties of an enzyme’s active site?

The enzyme’s tertiary structure.

How does an enzyme’s active site give it specificity?

It binds complementary substrates, forming an enzyme–substrate complex and giving the enzyme specificity for particular substrates and reactions.

What happens to the active site during substrate binding in the induced-fit model?

It changes shape, improving the fit and helping catalysis.

How does the lock-and-key model represent an enzyme’s active site?

As a rigid shape already exactly complementary to the substrate.

How does enzyme concentration affect reaction rate when substrate is sufficiently available and other conditions are constant?

The reaction rate increases as enzyme concentration increases.

Why can increasing enzyme concentration increase the reaction rate?

More enzyme provides more active sites, allowing more enzyme–substrate complexes to form per unit time.

Why does adding more enzyme have less effect when substrate availability is limiting?

There is not enough substrate to supply all the active sites.

Why does increasing substrate concentration initially increase reaction rate at a fixed enzyme concentration?

Enzyme–substrate complexes form more frequently.

How does increasing substrate concentration affect active-site occupancy?

A greater proportion of active sites are occupied.

Why does adding more substrate eventually stop increasing the reaction rate at a fixed enzyme concentration?

The enzymes become saturated, so the rate reaches its maximum.

What must become available for the reaction rate to increase beyond the maximum reached when enzymes are saturated?

More enzyme.

What effect do enzyme inhibitors have on enzyme-controlled reactions?

They reduce the reaction rate.

How does a competitive inhibitor interact with an enzyme?

It binds to the active site, competing with the substrate.

How does increasing competitive inhibitor concentration affect competition for the active site?

It increases competition with the substrate.

Why can increasing substrate concentration reduce the effect of a competitive inhibitor?

Substrate is more likely to occupy the active site.

How does a non-competitive inhibitor reduce catalysis?

It binds at a site other than the active site and alters the enzyme, reducing catalysis.

How does increasing non-competitive inhibitor concentration affect inhibition?

It generally increases inhibition.

Why does increasing substrate concentration not overcome non-competitive inhibition?

The inhibitor does not compete with substrate for the active site.

What is an enzyme’s optimum pH?

The pH at which its reaction rate is highest under the conditions considered.

How can a change in pH disrupt an enzyme’s tertiary structure?

It alters the charges on groups in the enzyme, potentially disrupting interactions that maintain the structure.

How can a pH-induced change in an enzyme’s active site reduce its activity?

It can reduce substrate binding or catalysis.

What can extreme pH do to an enzyme?

It can denature the enzyme, causing a lasting structural change and loss of activity.

Why does an enzyme-controlled reaction usually speed up as temperature rises toward the optimum?

Molecules gain kinetic energy, increasing the frequency of successful enzyme–substrate collisions.

What happens to an enzyme’s tertiary structure above its optimum temperature?

Interactions maintaining the structure are disrupted, increasingly denaturing the enzyme.

Why does enzyme denaturation reduce the reaction rate?

The active site changes, so fewer enzyme–substrate complexes form.

What effect do low temperatures have on enzyme-controlled reactions and the enzyme’s structure?

They slow the reaction but do not normally denature the enzyme.

How is an investigation of an enzyme-controlled reaction designed to test an independent variable?

Change a named independent variable, measure the reaction rate and control other relevant conditions.

How can the rate of an enzyme-controlled reaction be determined from substrate or product measurements?

Measure the change in substrate or product over a measured time.

How should the measurement method be used across treatments in an enzyme investigation?

Use the same measurement method across treatments.

Why repeat measurements in an enzyme investigation?

To assess variability and identify anomalous results.

How can enzyme investigation results be presented to examine the effect of the independent variable on enzyme activity?

Plot reaction rate against the independent variable and interpret the pattern in terms of enzyme activity.