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Biological molecules

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Which change breaks a glycosidic bond by hydrolysis?

  1. Adding water across the glycosidic bond
  2. Removing water from two glucose molecules
  3. Breaking only a hydrogen bond between chains
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Adding water across the glycosidic bond

Hydrolysis splits the covalent link using water.

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Which feature helps glycogen release glucose rapidly?

  1. Many chain ends from frequent branching
  2. Long unbranched chains with few terminal ends
  3. Beta-glucose chains packed into strong microfibrils
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Many chain ends from frequent branching

More terminal sites can be acted on by appropriate enzymes.

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A polysaccharide releases glucose very quickly when hydrolysed by an enzyme that acts only at chain ends. It is also insoluble. Which conclusion is best supported?

  1. It is made of beta-glucose units.
  2. It is highly branched, giving many chain ends.
  3. It is a long unbranched chain of glucose units.
  4. It is soluble in the cytoplasm.
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It is highly branched, giving many chain ends.

An end-acting enzyme works fastest when there are many ends, which branching supplies. Glycogen fits this.

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Complete hydrolysis of one triglyceride requires breaking how many ester bonds?

  1. Three, one for each fatty acid
  2. Two, one at each end of the glycerol
  3. One, linking the glycerol to all the fatty acids
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Three, one for each fatty acid

Three ester bonds attach the three fatty acids to glycerol.

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Which stabilises a typical alpha helix?

  1. Only disulfide bridges between four subunits
  2. Hydrogen bonds mainly between distant R groups
  3. Hydrogen bonds between backbone groups
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Hydrogen bonds between backbone groups

Regular backbone hydrogen bonding stabilises the helix.

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Which bond or interaction is NOT involved in maintaining the tertiary structure of a protein?

  1. Ionic bonds
  2. Glycosidic bonds
  3. Disulfide bridges
  4. Hydrophobic interactions
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Glycosidic bonds

Glycosidic bonds join sugars. Tertiary structure is held by hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions.

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How can changing pH alter a protein?

  1. By necessarily breaking every disulfide bridge
  2. By hydrolysing peptide bonds, which splits the chain into amino acids
  3. By changing R-group charges and disrupting ionic interactions
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By changing R-group charges and disrupting ionic interactions

This can change folding or binding-site properties.

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Why is haemoglobin soluble in water?

  1. Its haem groups contain iron ions, which carry a charge and so attract water.
  2. Its four chains are held together by covalent cross-links.
  3. Hydrophilic R groups on its outer surface form hydrogen bonds with water.
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Hydrophilic R groups on its outer surface form hydrogen bonds with water.

Hydrophobic R groups point inwards and hydrophilic R groups face outwards, so the molecule dissolves.

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Why is every third amino acid in a collagen chain glycine?

  1. Glycine's R group is small enough to fit in the centre of the triple helix.
  2. Glycine's polar R group makes collagen soluble, so it can travel in blood plasma.
  3. Glycine forms the covalent cross-links that join neighbouring collagen molecules into fibres.
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Glycine's R group is small enough to fit in the centre of the triple helix.

Its R group is a single hydrogen atom, so the three chains can pack tightly together.

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Question 1 of 8

Compare two glucose stores

4 marks

Compare amylose and glycogen as glucose stores, explaining a shared osmotic advantage and a difference in mobilisation. [4]

Give bond types, branching and a consequence.

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