Quiz 2

Question 1

It is through protein structure that genetic information is expressed

Answer 1

TRUE
-The 3-D structures and hence functions of proteins are dictated by their primary structures (or amino-acid sequences). These in turn are determined by the sequences of bases in the genes encoding the proteins. So, proteins are ‘gene products’, and it is through their synthesis, structure and activity that genetic information is used, or ‘expressed’.

Question 2

A protein having a net positive charge in solution at pH 7 will tend to move less readily towards the cathode (negative pole) as the pH increases

Answer 2

TRUE
-As the pH increases, [H+] decreases, and protons tend to dissociate from the protein. Its positive charge will diminish, and so it will move less readily towards the cathode.

Question 3

A linear chain of a polypeptide has a 5’ end and a 3’ end.

Answer 3

FALSE
-The polypeptide has two, chemically distinctly different ends, but these are an N terminus (with a free α-amino group) and a C terminus (with a free α-carboxyl group). 5’ and 3’ ends are characteristic of the polynucleotide chains of a nucleic acid.

Question 4

The body tends to move into positive nitrogen balance during pregnancy

Answer 4

TRUE
-As the body (and the developing foetus) grow in size during pregnancy, the nitrogen intake exceeds the nitrogen leaving the body. This is a state of positive nitrogen balance.

Question 5

Concerning skin. Keratin provides a barrier to UV radiation.

Answer 5

FALSE

-Melanin provides a barrier to UV radiation.

Question 6

Concerning enzymes: At ½ Vmax, the substrate concentration is equal to Km.

Answer 6

TRUE
-The maximum velocity that can be achieved depends on there being sufficient substrate available. By definition, Km is the substrate concentration at which half maximum velocity is achieved.

Question 7

The active form of human insulin contains two identical polypeptides

Answer 7

FALSE
-Active insulin contains two polypeptides, but they are not identical. They are products of the cleavage of a (larger) precursor polypeptide.

Question 8

The same chemical groups are involved in forming the bonds stabilising the beta-sheet as those involved in the bonds stabilising the a-helix.

Answer 8

TRUE

- In both cases, it’s the -NH and -C=O components of the polypeptide backbone.

Question 9

The appearance of sickle cell haemoglobin arises from a massive change in the primary structure of normal haemoglobin.

Answer 9

FALSE
-In fact, just one, particular amino-acid change, from glutamate to valine in a single position (5 in from the N terminus of the β chain of haemoglobin) is enough to change the three-dimensional structure of the molecule, and, potentially, its oxygen-carrying capacity. The amino-acid change is a result of a single base change on the DNA in the gene encoding the β chain. This type of change is known as a point mutation. In this case, it’s a T to A change, and that change coverts a particular DNA codeword that specifies glutamate to one that specifies valine.

Question 10

The deep fascia around muscles is composed of loose connective tissue.

Answer 10

FALSE
- It is composed of dense connective tissue in order to bind the muscle fibres into a cohesive bundle which can have a very defined action.

Question 11

In endocrine glands, ducts carry the hormones directly into blood vessels.

Answer 11

FALSE
-Hormones pass into blood vessels via the extracellular space not via ducts. The delivery of secretory products through ducts is associated with exocrine glands.

Question 12

Regarding electrical signalling by graded potentials: Graded potentials can signal stimulus intensity in their amplitude.

Answer 12

TRUE
-That is why they are called graded. You can think of a strong stimulus producing a large receptor (or generator) potential at a sensory receptor, or a lot of transmitter release evoking a large postsynaptic potential at a synapse.

Question 13

Concerning neurones: The dorsal root ganglia contain the cell bodies of efferent neurones.

Answer 13

FALSE
-The dorsal root ganglia contain the cell bodies of afferent neurones. Motoneurones, the classic example of an efferent neurone, have their cell bodies in the grey matter that forms the ventral horn of the spinal cord.

Question 14

Action potentials: Are transmitted along the membrane without decaying in amplitude

Answer 14

TRUE
-They are self-propagating. Depolarisation by the action potential depolarises the neighbouring section of membrane to threshold and stimulates more voltage-gated channels to open and generate a “new” all-or-none potential. The action potential will therefore continue to propagate itself without decaying so long as there are voltage-gated sodium channels in the membrane.

Question 15

Glutamate and glutamine are both genetically coded amino-acids

Answer 15

TRUE

-Both glutamate and glutamine appear in proteins.

Question 16

Concerning skin: The cells of the stratum spinosum are more superficial than the cells of the stratum granulosum

Answer 16

FALSE

-The cells of the stratum spinosum lie deeper than the cells of the stratum granulosum.

Question 17

A water-soluble protein, on denaturation, tends to come out of solution.

Answer 17

TRUE
- ‘Denaturation’ means loss of the 3-D structure of the active, ‘native’ protein. When this happens, previously hidden hydrophobic R groups are exposed to the water, and this may make the protein come out of solution.

Question 18

The major site of fatty acid catabolism in eukaryotic cells is the mitochondrion

Answer 18

TRUE
-β-oxidation occurs in the mitochondrion. This means that cells lacking mitochondria, like mature red blood cells, cannot use fatty acids as fuel molecules, and rely on hexose catabolism to generate ATP (by substrate phosphorylation).

Question 19

Cells of the keratinised stratified squamous epithelium that invests the skin are held together by junctions called dermatomes.

Answer 19

Dermatomes are areas of skin supplied by a single spinal nerve. Epithelial cells in the skin. Epithelial cells in the skin are held together by desmosomes.

Question 20

Concerning the nerve action potential: The depolarising phase is associated with a marked increase in permeability to Na+.

Answer 20

TRUE

-Depolarisation to threshold triggers voltage-gated Na+ channels, which are normally closed, to open.

Question 21

Concerning neurones: The spinal cord consists of grey matter surrounding the central white matter.

Answer 21

FALSE
-Grey matter (reflecting the preponderance of cell bodies) lies at the centre, and is surrounded by white matter (reflecting the tracts of myelinated axons).

Question 22

Glutamate and Glutamine are both genetically coded amino-acids.

Answer 22

TRUE

-Both glutamate and glutamine appear in proteins.

Question 23

Concerning enzymes: Cooperative effects between sub-unit components of a protein explain the substrate-binding behaviour of allosterically-affected enzymes.

Answer 23

TRUE
-Such co-operativity helps explain the sigmoid shaped curves often seen when initial reaction rate is plotted against substrate concentration for an allosterically affected enzyme.