Home / A level Biology 2.3 Proteins – Exam style question – Paper 2

A level Biology 2.3 Proteins – Exam style question – Paper 2

A level Biology Paper 2 - All Chapters
Question

Collagen is a fibrous protein that is found in many tissues in animals.

(a) Describe the structure of a collagen molecule and the structure of a collagen fibre.

(b) Some amino acids in collagen can be modified to improve the stability of the protein. For example, the amino acid lysine can be modified to form hydroxylysine.

Fig. 2.1 shows a disaccharide bonded to the amino acid hydroxylysine in a collagen molecule. The disaccharide is made from two monosaccharides, which are indicated by the labels D and E in Fig. 2.1.

(i) Give the precise name of the monosaccharide labelled D in Fig. 2.1.

(ii) On Fig. 2.1, label the glycosidic bond with the letter G. Write your answer on Fig. 2.1.

(iii) On Fig. 2.1, draw a circle around the R group of hydroxylysine and label the circle with the letter R. Write your answer on Fig. 2.1.

(c) Osteogenesis imperfecta is a disease that results from a deficiency in collagen. Suggest how a named tissue or structure is affected in a person who has this disease.

▶️ Answer/Explanation
Solution

(a)

Collagen molecule:

  • Composed of three polypeptide chains wound into a triple helix structure.
  • Each chain has a repeating Gly-X-Y sequence (where X is often proline and Y is often hydroxyproline).
  • Stabilized by hydrogen bonds between the chains.

Collagen fiber:

  • Formed by cross-linking between multiple collagen molecules via covalent bonds.
  • Molecules are arranged in a staggered, parallel fashion, providing tensile strength.
  • Fibers are further organized into fibrils for structural support.

(b)(i) α-glucose (alpha-glucose)

Explanation: Monosaccharide D is identified as α-glucose based on its structure in the disaccharide.

(b)(ii) The glycosidic bond (G) should be labeled between the two monosaccharides (D and E).

Explanation: This bond connects the two sugar units in the disaccharide.

(b)(iii) The R group of hydroxylysine is NH2CH2CHCH2CH2 and should be circled and labeled “R”.

Explanation: The R group is the side chain specific to hydroxylysine.

(c) Bone tissue becomes brittle and prone to fractures.

Explanation: Collagen provides flexibility and strength to bones. In osteogenesis imperfecta, deficient collagen leads to fragile bones that break easily.

More A level Biology Paper 2 Question.................
Scroll to Top