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Proteins

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Question 6

Two enzymes, X\mathbf{X}X and Y\mathbf{Y}Y, are proteins with quaternary structure that catalyse the same reaction, but they have different amino acid sequences.

1.

Define the tertiary structure of a protein.

[1]
2.

Explain how two enzymes with different amino acid sequences can catalyse the same reaction.

[2]
3.

Scientists investigated the effect of temperature (25 ∘C25\ ^\circ\text{C}25 ∘C and 60 ∘C60\ ^\circ\text{C}60 ∘C) on the activity of enzymes X\mathbf{X}X and Y\mathbf{Y}Y.

Figure 1 shows their results.

Two line graphs side-by-side representing Figure 1. Both plots show concentration of substrate in arbitrary units on the y-axis, from 0.0 to 1.2, against time in minutes on the x-axis, from 0 to 20. The left graph is labeled "25 °C" and has three curves: a solid black line (Control) descending slowly from 1.0 to 0.05 at 15 minutes; a dashed black line (Enzyme X) dropping steeply to 0.05 by 2 minutes then flatlining; and a solid grey line (Enzyme Y) dropping steadily to 0.05 by 5 minutes then flatlining. The right graph is labeled "60 °C" and has three curves: the solid black Control curve descending slowly from 1.0 to 0.05; the dashed Enzyme X curve dropping steeply to 0.05 by 2 minutes; and the solid grey Enzyme Y curve overlapping almost exactly with the slow-descending Control curve. Key: Solid black line = Control, Dashed black line = Enzyme X, Solid grey line = Enzyme Y.

Describe what the scientists should place in the control tubes in this investigation.

[3]
4.

State three conclusions you can make from the results in Figure 1.

[3]

Proteins Questions

  1. A Level
  2. /Biology
  3. /Proteins

Practise AQA A Level Biology Proteins with exam-style questions for A Level Biology. 22 questions covering General properties of proteins and Many proteins are enzymes, matched to the AQA A Level Biology (7402) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.

Question bank