The graph shows the effect of changes in pH on the activity of the enzyme lysozyme. Describe the effect of pH on this enzyme.

Every enzyme acts best at a particular pH called optimum pH. The enzyme shows its maximum catalytic activity at this optimum pH. For lysozyme, the optimum pH ranges between 5 and 6 at which it will show its maximum catalytic activity in a solution. The maximum activity or optimum pH of lysozyme is pH 5. The activity of lysozyme gradually increases between pH 2 and pH 5, and decreases from pH 5 to pH 10. The activity of this enzyme becomes very low at pH 2 and pH 10.

The graph shows the effect of changes in pH on the activity of the enzyme lysozyme. Explain why pH affects the activity of the enzyme.

Enzyme is protein in nature. The pH is a measure of the amount of H+ ions in a solution that can react with the different R-groups of enzyme molecules leading to ionic bond breakage and alteration in the three-dimensional structure of the enzymes. This is called denaturation of enzymes that can significantly affect their functioning. Denaturation of enzyme occurs when the pH of the solution does not match the optimum pH required for a particular enzyme for its activity. pH is a measure of the hydrogen ion concentration; hydrogen ions are positively charged; The hydrogen ions can interact with the R groups of amino acids, and it affects ionic bonding or affects ionisation of R group. This phenomenon affects tertiary structure or 3D shape of enzyme, therefore, substrate may not fit active site.

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Biology for Cambridge International AS & A Level coursebook 2nd Edition Digital Access>Chapter 3 - Enzymes>EXAM-STYLE QUESTIONS>Q 1

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The diagram shows an enzyme and two inhibitors of the enzyme, X and Y. Which of the following describes the two inhibitors?

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Important Questions on Enzymes

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Biology for Cambridge International AS & A Level coursebook 2nd Edition Digital Access>Chapter 3 - Enzymes>EXAM-STYLE QUESTIONS>Q 2

In a reaction controlled by an enzyme, which of the following graphs shows the effect of substrate concentration on the rate of the reaction, assuming the reaction is allowed to go to completion?

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Biology for Cambridge International AS & A Level coursebook 2nd Edition Digital Access>Chapter 3 - Enzymes>EXAM-STYLE QUESTIONS>Q 3

The graph shows the progress of the digestion of starch by the enzyme salivary amylase. Why does the reaction slow down?

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Biology for Cambridge International AS & A Level coursebook 2nd Edition Digital Access>Chapter 3 - Enzymes>EXAM-STYLE QUESTIONS>Q 4

An enzyme with a high affinity for its substrate has a:

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Biology for Cambridge International AS & A Level coursebook 2nd Edition Digital Access>Chapter 3 - Enzymes>EXAM-STYLE QUESTIONS>Q 5

If methylene blue dye is added to a suspension of yeast cells, any living cells remain colourless. However, any dead cells are stained blue. This fact was used to carry out an investigation into the rate at which yeast cells were killed at two different temperatures (at high temperatures the yeast enzymes will be denatured). The results are shown in the diagram.

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