y3 biology chp4

enzymes

what are enzymes?

Enzymes are proteins that function as biological catalysts. They catalyse or speed up the rate of chemical reactions and remian chemically unchanged at the end of the reaction. They work by lowering activation energy of a reaction.

What are the reactions that enzymes can catalyse?

They can build up complex substances and break down complex substances

Explain the lock and key hypothesis

An enzyme has a specific three-dimensional shape which contains an active site. Only a substrate with a 3D shape complementary to that of the active site can fit into the enzyme to form an enzyme-substrate complex. Chemical reactions will then occur and the substrate is converted into products. The products will then detach from the active site. Once the products leave, the enzyme’s active site is free to bind to another substrate molecule. This means the enzyme can be reused and hence are required only in minute quantities. The enzyme remains unchanged at the end of the reaction.

What happens to enzymes at very low temperatures?

Enzymes are less active at very low temperatures. The kinectic energy is low at low temperatures. Hence, chances of substrate molecules colliding with enzymes are very low.

What happens to the enzymes as the temperature increases?

When the temperature increases, heat energy supplied to the enzyme and substrate molecules increases. This causes the molecules to collide more frequently as kinetic energy in enzymes and substrate molecules increases, this increases the rate of effective collisions. Thus, the rate of formation of enzyme-substrate complex increases, increasing the rate of formation of product to increase. Usually the enzyme is twice as active for every 10°C rise in temperature until optimum temperature is reached. The optimum temperature is the point when the rate of reaction is the highest and enzyme is most active.

what happens to enzymes beyond optimum temperature?

Beyond optimum temperature, enzyme activity decreases as polypeptide chains of enzyme molecules unfold as the high temperature breaks the bonds within the enzyme and changes its 3D shape. The active site is now lost and the enzyme is denatured. The substrate molecules can no longer bind to the enzyme molecules to form enzyme-substrate complexes, as the substrate can no longer fit into the enzyme’s active site.

What happens to organisims at prolonged exxposure to high temperature? Explain in terms of enzymes

Organisms may be killed by prolonged exposure to high temperatures. This is because enzymes in their cells are denatured and the chemical reactions proceed too slowly to mantain life.

What happens at optimum pH?

The rate of reaction is maximum at optimum pH. The optimum pH is the pH at which maximum rate of reaction occurs. This results in the highest number of enzyme-substrate complexes formed per unit time, which means the rate of treaction is at its maximum.

what happens when pH changes drastically?

Polypeptide chains of enzyme molecules unfold as ionic forces of attraction holding the chains together are overcome. The active site thus loses its specific three-dimensional shape. Substrate molecules can no longer bind to the enzyme molecules to form enzyme-substrate complex as they no longer have complementaty shape and so will not fit together. The enzyme loses its catalytic function and denatures.

How does the concentration of substrate affect the rate of reaction?

The rate of enzymatic reaction increases proportionally with increasing substrate concentration, assuming the other factors are kept constant.

Why will it reach a point when the rate of reaction no longer increases despite the substrate concentration continuing to increase?

This is because all active sites of enzyme molecules are bound to substrate molecules at any given time. When all the active sites of enzyme molecules are saturated, thge rate of reaction will remain constant. Adding more substrate molecules cannot affect the rate of reaction, therefore, it is no longer the limiting factor

What happens at low substrate concentration?

At low substrate concentration, the frequency of effective collisions between enzyme and substrate is low, hence the rate of forming enzyme-substrate complexes is low, thus, the rate of reactuon is low as number of products formed per unit time is low.

What happens at increasing substrate concentration?

As the substrate concentration increases, the chance of effective collisions between enzyme and substrrate increases. This increases the rate of forming enzyme-substrate complexes, hence the rate of reaction increases as number of products formed per unit time increases.

What happens if all available enzyme active sites are occupied?

Even though the substrate concentration continues to increase, all available enzyme active sites are occupied by a substtate. The rate of effective collisuions has reached itys maximum limit. Hence, the rate of forming enzyme-substrate complexes does not increase further and rate of reacrtion remains the same.

What becomes the limiting factor at higher substrate concentrations?

The number of active sites

Why does the rate of reaction change over time if no other variable is changed?

As time progresses, more substrates are used up and converted into products. Hence, there is lesser substrate, resulting in fewer effective collisions with the enzyme and substrate, causing fewere enzyme-substrate complexes to be formed which results in a lower rate of reaction over time.

What happens as the concentration of enzyme increases?

As enzyme concentration increases, more active sites are available, the frequency of effective collisions between the enzyme and substrate molecules increases. More enzyme-substrate complexes are formed and thus the rate of reaction increases.

What happens at very high enzyme concentrations?

At very high enzyme concentrations, if the concentration of substrate molecules is limiting, an increase in enzyme concentration would not result in any further increase in the rate of reaction. This is because there are insufficient substrate molecules to occupy all available active sites; hence the rate of reaction is now dependent on substrate concentration.

What happens at low enzyme concentration?

There is great competition for the active sites and the rate of reaction is low. As the enzyme concentration is low, fewer enzyme-substrate complexes form as the frequency of effective collisions with the enzyme and the substrate is low, resulting in a slower overall reaction rate as the rate of products formed over time is low.