Enzymes Questions and Answers

What is the temperature co-efficient of most enzyme-controlled reactions?

The diagram illustrates enzyme action.

Fig. 2.1 shows two types of enzyme inhibition. In one type, both the substrate and an inhibitor are able to bind directly to the enzyme's active site, so the inhibitor competes with the substrate for that site. What is this type of inhibition called?

Fig. 2.1 shows two types of enzyme inhibition. In the second type, the substrate still binds normally to the active site, but an inhibitor instead binds to a separate allosteric site on the enzyme, which changes the shape of the active site. What is this type of inhibition called?

In competitive inhibition, the inhibitor competes with the substrate for the enzyme's active site. At a sufficiently high substrate concentration, the reaction rate can eventually reach the same ___ as the uninhibited enzyme, because excess substrate molecules out-compete the inhibitor for the active site.

In an enzyme-catalysed reaction, the potential energy of the substrates at the start of the reaction is 50 kJ, and the maximum potential energy reached along the reaction pathway, with the enzyme present, is 68 kJ. Calculate the activation energy of this catalysed reaction, in kJ.

In a school practical, 2 cm3 of 2.0M hydrogen peroxide is added to 2 cm3 of an active (unboiled) yeast suspension in a test tube, and a glowing splint is immediately inserted into the tube above the mixture. What happens to the glowing splint?

In the same test (2 cm3 of 2.0M hydrogen peroxide added to 2 cm3 of active, unboiled yeast suspension), what is seen in the reaction mixture itself, separate from the glowing-splint test?

A yeast suspension is boiled for 5 minutes, then cooled under running tap water. Hydrogen peroxide is added and a glowing splint is inserted, exactly as was done with an unboiled sample. What is observed?

Name the enzyme present in yeast that is responsible for breaking down hydrogen peroxide into water and oxygen.

When catalase breaks down hydrogen peroxide in yeast, which gas is produced?

A yeast suspension that was boiled for 5 minutes and then cooled shows no bubbling and does not relight a glowing splint when hydrogen peroxide is added, unlike an unboiled sample of the same yeast suspension. Why?

In this investigation catalase activity was measured by timing how long it took manometer fluid to rise 5 cm in a boiling tube containing potato discs, buffer and hydrogen peroxide. After adding the hydrogen peroxide and replacing the bung, the tube was shaken gently. State the reason the tube was shaken.

In this investigation, catalase activity was tested in buffer solutions at pH3, 4, 5, 6, 7 and 8, so that the rate of the reaction could be compared across the different pH values. State why buffer solutions, rather than plain solutions of acid or alkali, were necessary for this investigation.

Catalase activity was measured over the pH range 3 to 8. As the pH rises from pH3 towards pH7, the rate of the reaction increases. What happens to the ionisable groups of catalase's active site as the pH rises over this range?

As the ionisable groups of catalase's active site are modified between pH3 and pH7, what specifically is disrupted, allowing the reaction rate to rise?

Between pH3 and pH7, disruption of the ionic bonding that maintains catalase's shape is linked to a rising reaction rate, without yet denaturing the enzyme. What effect does this disruption have on the active site over this range?

Above pH7 (towards pH8), the rate of the catalase reaction falls. What happens to catalase's ability to form enzyme-substrate (ES) complexes over this range?

Table 1.1 in this practical dilutes a 0.005 mol/dm3 glucose stock solution with distilled water to make five standards, keeping the total volume at 5 cm3. Row 1 mixes 1 cm3 stock with 4 cm3 water (0.001 mol/dm3); row 2 mixes 2 cm3 stock with 3 cm3 water (0.002 mol/dm3); row 3 mixes 3 cm3 stock with 2 cm3 water (0.003 mol/dm3). Following this same pattern, how many cm3 of the 0.005 mol/dm3 glucose stock and how many cm3 of distilled water are needed to make the 0.004 mol/dm3 standard?

Using the same 5 cm3-total dilution series as Table 1.1 (1 cm3 stock + 4 cm3 water = 0.001 mol/dm3, up to 3 cm3 stock + 2 cm3 water = 0.003 mol/dm3), how many cm3 of the 0.005 mol/dm3 glucose stock and how many cm3 of distilled water are needed to make the 0.005 mol/dm3 standard itself?

In a Benedict's test, five glucose standards from 0.001 to 0.005 mol/dm3 are each mixed with Benedict's solution and heated in a boiling water bath for 5 minutes. Which colour is expected for the LOWEST standard, 0.001 mol/dm3?

In a Benedict's test, five glucose standards from 0.001 to 0.005 mol/dm3 are each mixed with Benedict's solution and heated in a boiling water bath for 5 minutes. Which colour is expected for the HIGHEST standard, 0.005 mol/dm3?

In this practical, starch solutions A, B and C were each hydrolysed by solution P then tested with Benedict's solution. The expected results were: tube A, dark orange (concentration greater than 0.005 mol/dm3); tube B, green (0.001 mol/dm3); tube C, yellow (0.0025 mol/dm3). Ranking the three tubes from LOWEST to HIGHEST reducing sugar concentration, what is the correct order?

Starch solutions A, B and C were hydrolysed for 30 minutes by the same enzyme solution P, then tested for reducing sugar. Tube A (highest original starch concentration) produced the most reducing sugar; tube B (lowest original starch concentration) produced the least. Why does a solution with a higher original starch concentration produce more reducing sugar in the same fixed reaction time?