IB Biology SL B1.2 Proteins questions

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Type
Multiple choiceWritten
Difficulty
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Question 1

Paper 2Easy6 marks

A student exposes equal samples of the same enzyme to different conditions for 10 minutes. The student then measures the activity of each sample at pH 7 and 25 °C.

Conditions during exposureRelative enzyme activity afterwards (% of untreated control)
pH 7, 25 °C (untreated control)100
pH 7, 80 °C8
pH 2, 25 °C12
(a)

State three features of polypeptide chains that allow a wide variety of polypeptides to exist.

[3]
(b)

Use the results in the table.

(i)

Identify the exposure condition that resulted in the lowest enzyme activity.

[1]
(ii)

State the term for the change in protein structure that can be caused by high temperature or extreme pH, and state one effect of this change on enzyme function.

[2]

Question 2

Multiple choiceMedium1 mark

Two polypeptides each contain 80 amino acids and the same number of each amino-acid type, but the amino acids are in different orders. Which statement correctly links this difference to a possible effect of a large pH change or high temperature?

Show answer and explanation

Answer: B. Polypeptides with the same amino-acid composition can differ when their amino acids are in a different order. A large pH change or high temperature could cause denaturation, changing protein structure.

A: treats composition as sufficient to identify a polypeptide, overlooking amino-acid order.
C: confuses a change in protein structure with a change in amino-acid sequence.
D: assumes structure cannot change unless the amino-acid order changes.

Remember: amino-acid order distinguishes polypeptides, while denaturation changes protein structure.

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