EduNinja

[Maximum number: 6]

Saccharomyces cerevisiae is a unicellular fungus that is important in the brewing and baking industries.

Fig. 4.1 is a diagram of a transmission electron micrograph of S. cerevisiae.

Fig. 4.1

(a)

The hydrolysis of trehalose is catalysed by two different enzymes produced by S.cerevisiae, regulatory trehalase and non-regulatory trehalase.

A study was carried out to compare regulatory trehalase and non-regulatory trehalase extracted from S. cerevisiae.

The results of the study showed that:
- regulatory trehalase had a higher $\mathrm{K}_{\mathrm{m}}$ value (Michaelis-Menten constant) than non-regulatory trehalase
- the optimum pH of regulatory trehalase was pH 7.0-7.8
- the optimum pH of non-regulatory trehalase was pH 4.5-5.0.

[ 3 ]

(i)

Explain what is meant by a higher $\mathrm{K}_{\mathrm{m}}$ value.

[ 2 ]

any two from (higher $K_{m}$ enzyme)

has a lower affinity for its substrate ;
A binds substrate less easily needs a higher concentration of substrate to reach, $\mathrm{V}_{\text {max }} /$ maximum activity $/ \frac{1}{2} \mathrm{~V}_{\text {max }}$ ;
less likely to be saturated with substrate ;
variations in substrate have greater effect on rate of reaction ;

(ii)

Explain whether both types of trehalase, regulatory and non-regulatory, can be described as intracellular enzymes.

[ 1 ]

(b)

Saccharomyces boulardii is a strain of S. cerevisiae. It has been researched for its possible health benefits for some gut diseases.

Researchers investigating trehalase extracted from S. boulardii concluded that only one type of trehalase was present in the extract.

Fig. 4.3 shows the effect of pH on the activity of the trehalase extracted from S. boulardii.

Fig. 4.3

With reference to Fig. 4.3 and to the two different types of trehalase enzyme produced by S. cerevisiae, state and explain what can be deduced about the type of trehalase present in S. boulardii.

[ 3 ]

[Maximum number: 3]

Prostaglandins are small lipids produced in many tissues of the body. One role of prostaglandins is to cause inflammation at the site of an injury or infection. Inflammation is the normal first response of the immune system to injury or infection.

Cyclooxygenase (COX) is an enzyme that catalyses one of the steps in the reaction pathway for the formation of prostaglandins from phospholipids. The reaction pathway occurs in the smooth endoplasmic reticulum (SER) of cells. Part of the reaction pathway is shown in Fig. 1.3.

Fig. 1.3

Sometimes inflammation can have side-effects, such as pain. Aspirin is a drug that can be used to reduce these side-effects.

Aspirin reduces the catalytic activity of the COX enzyme by modifying the R-group of one of the amino acids.

Suggest how modifying the R-group of an amino acid in the COX enzyme can reduce the catalytic activity of the enzyme.

CAIE A-Level Biology AS 3 Enzymes Topic Practice

Question 1

Question (a)

Question (i)

Question (ii)

Question (b)

Question 2