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Biomolecules: structure explains function

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What differs between the usual ring forms of alpha- and beta-glucose?

  1. The hydroxyl group at carbon 4 is reversed instead.
  2. Orientation of the hydroxyl group at carbon 1.
  3. The number of carbon atoms.
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Orientation of the hydroxyl group at carbon 1.

This small structural difference affects the polymers formed.

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Which feature helps cellulose perform a structural role?

  1. Many hydrogen bonds hold aligned chains together.
  2. It dissolves readily to produce many separate glucose molecules.
  3. Its chains contain only alpha-1,6 bonds.
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Many hydrogen bonds hold aligned chains together.

The microfibrils resist tension in plant cell walls.

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What makes a phospholipid suited to a membrane bilayer?

  1. Three fatty-acid tails give the molecule a polar head.
  2. Its tails are hydrophilic and face the water on both sides.
  3. A hydrophilic head and hydrophobic tails orient differently in water.
  4. Its saturated tails form kinks that keep the whole bilayer fluid at body temperature.
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A hydrophilic head and hydrophobic tails orient differently in water.

Heads face aqueous environments and tails form the interior.

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Which link is broken when a polypeptide backbone is hydrolysed?

  1. Only a hydrogen bond between side chains.
  2. Peptide bond.
  3. Glycosidic bond.
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Peptide bond.

Hydrolysis uses water to break the covalent -CO-NH- link.

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A polypeptide of 150 amino acids is completely hydrolysed. How many water molecules are used?

  1. 150
  2. 300
  3. 149
  4. 75
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149

A linear chain of 150 amino acids has 149 peptide bonds, and each hydrolysis uses one water molecule.

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Which statement about an alpha-helix is correct?

  1. It is the overall three-dimensional shape of one entire polypeptide.
  2. Hydrogen bonds between backbone groups stabilise its local coiling.
  3. Hydrogen bonds between R groups define the helical backbone.
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Hydrogen bonds between backbone groups stabilise its local coiling.

The peptide backbone remains intact while adopting this regular arrangement.

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Which effect most directly links altered pH to altered folding?

  1. The primary sequence alone sets folding, so charge changes cannot alter it.
  2. Changes in ionisation alter ionic interactions within the protein.
  3. Changing pH hydrolyses peptide bonds, so the chain breaks into amino acids.
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Changes in ionisation alter ionic interactions within the protein.

Altered charge can destabilise the conformation.

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Why is reversible binding essential?

  1. It keeps all four oxygen sites occupied even in oxygen-poor tissue.
  2. It allows haemoglobin to store oxygen inside red cells for later use by the cell itself.
  3. It allows oxygen loading and later unloading.
  4. It means oxygen forms permanent bonds with the polypeptide backbone.
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It allows oxygen loading and later unloading.

A transporter must deliver the substance it picks up.

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Which feature of haemoglobin does NOT help it transport oxygen?

  1. Each subunit has a haem group with Fe2+
  2. Hydrophilic R groups face outwards
  3. Peptide bonds join its amino acids
  4. Oxygen binds reversibly
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Peptide bonds join its amino acids

Every protein has peptide bonds. They do not explain oxygen transport, unlike haem, reversibility and solubility.

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Question 1 of 10

Explain a haemoglobin difference between species

5 marks

An invented high-altitude goose species has haemoglobin with a higher affinity for oxygen than a lowland goose species. Their beta chains differ at one position: the lowland species has an amino acid with a large hydrophobic R group, and the high-altitude species has one with a small R group. Explain how this single difference could raise oxygen affinity, and why a higher affinity helps at high altitude. [5]

Amino acid -> R group -> bonds -> tertiary -> quaternary -> affinity. Then link to low oxygen partial pressure.

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