A-LevelBiologyBiological molecules9700/12 · Oct/Nov 2024 · Q71 Mark
The table shows some information about the polypeptides that make up haemoglobin. α-globin: total number of amino acid residues in polypeptide chain: 141 position of amino acid cysteine in polypeptide chain: 104 β-globin: total number of amino acid residues in polypeptide chain: 146 position of amino acid cysteine in polypeptide chain: 93 and 112 Scientists studied the region of the β-globin polypeptide chain containing the amino acid cysteine at position 93. They found that: • this region faces outwards when no oxygen is attached to the haem group • this region faces inwards when oxygen is attached to the haem group • replacing cysteine with a different amino acid reduces the Bohr shift. What can be concluded from the information about cysteine in haemoglobin?
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AMore than 1% of the amino acids in one haemoglobin protein are cysteine.
BIn α-globin, there is a cysteine closer to the end of the polypeptide chain with an unreacted carboxyl group than in β-globin.
CThe replacement of the cysteine at position 93 in β-globin decreases the affinity of haemoglobin for oxygen at low pH.
DThe binding of oxygen to the haem group causes the region of β-globin containing cysteine at position 93 to become more hydrophilic.
✓ Correct answer
A: More than 1% of the amino acids in one haemoglobin protein are cysteine.
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