Explain the relationship between enzyme activity and concentration of the substrate.

Determine the Michaelis constant \({K_{\text{m}}}\) from the graph.

Describe why competitive inhibition may take place.

Explain the effect of competitive inhibition on \({V_{{\text{max}}}}\) and \({K_{\text{m}}}\).

On the graph of effect of concentration on rate of reaction on page 10, sketch the expected curve for non-competitive inhibition.

As [S] increases, more enzyme molecules can link with substrate molecules (and rate increases);

once all enzyme molecules are occupied/enzyme sites used up, rate cannot increase anymore/has no effect;

\({\text{0.7 (mmol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{)}}\);

Allow 0.6–0.8. If wrong units, then no mark.

inhibitor molecules are very similar to the substrate and the enzymes cannot distinguish them / are able to bind to/occupy the active sites / OWTTE;

same \({V_{{\text{max}}}}\);

at high [S], impact of inhibitor reduced / possible to reach same maximum rate;

the curve is less steep (than without inhibition) / the enzyme is less effective / OWTTE;

so \({K_{\text{m}}}\) higher (than without inhibition);

curve on graph levelling off below original line;

K_m should be approximately the same, V_max should be smaller.

Instead of explaining the relationship between enzyme activity and concentration of the substrate, many candidates just described the relationship indicated by the graph.

Many candidates were correctly able to describe why competitive inhibition may take place. On the other hand, others misinterpreted the question and wrote about the need for the inhibition.

Where they had to explain, in several cases it was not well answered.

When drawing the graph several candidates did not take into account that \({K_m}\) should be the same.