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IB Biology SL B1.2 Proteins Questions

Practise IB Biology SL B1.2 proteins through amino acid structure, peptide bonds, condensation reactions, dietary requirements and structure–function links.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • Identify an amino acid’s alpha carbon, amine group, carboxyl group, hydrogen and variable R-group, and relate protein composition to C, H, O, N and usually S.
  • Explain amino-acid condensation and peptide-bond formation, identify dipeptide or polypeptide products and water release, and distinguish condensation from hydrolysis.
  • Distinguish essential amino acids that must come from dietary protein from non-essential amino acids made by the body, and explain limiting supply and protein-deficiency consequences.
  • Explain how amino-acid type, number and order create a wide variety of polypeptide sequences and proteomes.
  • Explain how high temperature or unsuitable pH denatures proteins by changing their structure and reducing biological activity.

Covered syllabus points

B1.2.1—Generalized amino acid structureB1.2.2—Condensation reactionsB1.2.3—Dietary amino acidsB1.2.4—Infinite variety of peptide chainsB1.2.5—Effect of pH and temperature

Question 1

[Maximum number: 1]

The diagram shows the molecular structure of the amino acid leucine.

Figure for Question 1 — IB Biology SL

Draw a circle on the diagram to enclose the carboxyl group.

Question 2

[Maximum number: 2]

A short base sequence of mRNA and a table of the genetic code are shown below.
Sequence of mRNA
AUGAGCCGAAGGUAGCUG
Table of the genetic code

Table for Question 2 — IB Biology SL

Question (a)

(a)

The diagram shows a section of a polypeptide.

Figure for Question (a) — IB Biology SL
[ 2 ]

Question (i)

(i)

Annotate the diagram to show a peptide bond between two amino acids.

[ 1 ]

Question (ii)

(ii)

State the type of reaction that removes water while linking amino acids together to form polypeptides.

[ 1 ]

Question 3

[Maximum number: 2]

Some of the twenty amino acids that are linked together to make polypeptides in human cells are essential in the diet and others are not. Distinguish between essential and non-essential amino acids.

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