Chapter 4 Self-test questions

. Which of the following statements about amino acids is correct?

Amino acids are classified according to the structures and properties of their side chains.

Amino acids are uncharged at neutral pH.

Amino acids in proteins are mainly in the D-configuration.

Twenty four amino acids are commonly used in protein synthesis.

. Which type of bonding is responsible for the secondary structure of proteins?

Disulphide bridges between cysteine residues.

Hydrogen bonding between the C=O and N-H groups of peptide bonds.

Peptide bonds between amino acids.

Salt bridges between charged side chains of amino acids.

. Which term below best defines the 'quaternary structure' of a protein?

The arrangement of two or more polypeptide subunits into a single functional complex.

The folding of the polypeptide backbone in three-dimensional space.

The interaction of amino acid side chains.

The sequence of amino acids in a polypeptide chain.
.

. Which of the following statements about collagen is correct?

Collagen contains a high proportion of hydroxylated proline residues.

Collagen is a globular, intracellular protein.

Post-translational modification of collagen involves vitamin A.

The structure of collagen consists of a superhelix of three á helices twisted together.

. Which of the following statements about haemoglobin is correct?

2,3-Bisphosphoglycerate (BPG) increases the affinity of haemoglobin for oxygen.

Deoxygenated haemoglobin has a higher binding affinity for protons than has oxyhaemoglobin.

Haemoglobin has a higher affinity for oxygen than does myoglobin.

One molecule of haemoglobin binds sixteen molecules of oxygen-four per subunit.

. Which of the following amino acids is mostly likely to disrupt an alpha helix?

Proline.

Leucine.

Glycine.

Valine.

. Which of the following most accurately describes how secondary structures in proteins are stabilized?

Through ionic bonds operating between oppositely charged amino acid side chains.

Through covalent bonds joining different parts of the peptide backbone.

Through hydrogen bonds between different amino acid side chains.

Through hydrogen bonds joining different parts of the peptide backbone.

. Which amino acid can form disulphide bonds?

Glycine.

Proline.

Glutamate.

Cysteine.

. Which of the following pairs of amino acids might contribute to protein conformation by forming electrostatic interactions?

Glycine and leucine.

Glutamate and lysine.

Phenylalanine and tyrosine.

Lysine and arginine.

. Which of the following best describes a protein domain?

The -helical portion of a protein.

A discrete region of polypeptide chain that has folded into a self-contained three-dimensional structure.

The -pleated sheet portion of a protein.

A feature that rarely occurs in globular proteins.

. As haemoglobin binds oxygen molecules, its affinity for oxygen increases, driving the binding of further oxygen molecules. Which term best describes this phenomenon?

Catalysis.

Saturation.

Allostery.

Isomerism.

. Which of the following statements correctly describes the behaviour of the haemoglobin protein in sickle-cell disease?

The haemoglobin protein dissociates into four subunits.

The haemoglobin protein lacks a haem group.

Neighbouring haemoglobin proteins aggregate together.

The haemoglobin protein possesses an iron atom in the Fe (III) form rather than the normal Fe (II) form.

Chapter 4 Self-test questions

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