Biology 9700 · AS & A Level · Transport of oxygen and carbon dioxide

Transport of oxygen and carbon dioxide — practice question

The enzyme carbonic anhydrase has been identified in a wide variety of organisms and functions as a catalyst in many tissues. Research has shown that the protein structure of the enzyme differs, and that the number and arrangement of introns and exons in the gene coding for the enzyme also differ. All carbonic anhydrase enzymes catalyse the same reversible reaction, shown in Fig. 4.1: $\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-$
(a)[2]

Using Fig. 4.1, name X and Y.

(b)[1]

Carbonic anhydrase enzymes may have different primary structures. Suggest how they are still able to catalyse the same reaction despite these differences.

(c)[3]

Eukaryotic protein-coding genes contain introns and exons. Outline the similarities and differences between introns and exons in genes that code for proteins such as carbonic anhydrase.

(d)[2]

Red blood cells contain two isoforms, CA1 and CA2. Suggest the location of CA1 and CA2 in red blood cells and explain your answer.

(e)[1]

Isoform CA6 is part of human breast milk. Mammary gland cells place CA6 into Golgi vesicles so that it can be released from the cells. Name the transport mechanism linked to CA6 secretion.

(f)[3]

In some epithelial cells in the eye, human CA isoforms help to form the clear fluid called aqueous humour. Excess enzyme activity may cause a dangerous rise in pressure inside the eye and lead to a condition known as glaucoma. Acetazolamide is a therapeutic drug used in the treatment of glaucoma. It acts as a reversible non-competitive inhibitor. Describe the mechanism of action of acetazolamide as a reversible non-competitive inhibitor of carbonic anhydrase.

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