Quiz 2 true or false

Question 1

Scurvy is caused by a defect in collagen metabolism.

Answer 1

TRUE
-Scurvy is caused by lack of dietary vitamin C necessary for the production of the enzyme that catalyses conversion of proline to hydroxyproline in collagen.

Question 2

Much of collagen primary structure consists of repeats of the 3-monomer structure ( - glutamate - X - proline - ).

Answer 2

FALSE

-Much of collagen’s primary structure consists of ( - glycine - X - proline - ) repeats.

Question 3

Once absorbed into intestinal cells, dietary free fatty acids are released into the blood for transport to other tissues.

Answer 3

FALSE
-The major products of fat digestion are free fatty acids and monoacylglycerols (monoglycerides) in which a fatty acid is still esterified to the -OH of the inner carbon of the glycerol. Once absorbed, these products of digestion are re-converted into triacylglycerols (triglycerides) and assembled, with proteins, into particles called chylomicrons for transport via the lymph to the blood.

Question 4

With regard to membrane potentials: Excitatory postsynaptic potentials are all-or-none potentials.

Answer 4

FALSE
-They are graded potentials which can vary, for example, according to the amount of neurotransmitter that is released . It is the summation of graded postsynaptic potentials that allows synaptic integration.

Question 5

Digestion of dietary protein begins in the mouth

Answer 5

FALSE
- ‘Digestion of dietary protein begins in the stomach, with the action of pepsin. Digestion of dietary polysaccharide begins in the mouth, when an amylase acts on starch.

Question 6

Fatty acids and acetyl CoA are not glucogenic

Answer 6

TRUE
-The pyruvate dehydrogenase-catalysed oxidative decarboxylation of pyruvate into acetyl CoA is virtually thermodynamically irreversible under the conditions occurring in cells. Further, there is no net synthesis of oxaloacetate (or any other gluconeogenic precursor) by metabolism through the citric acid cycle. Therefore, although net flow of carbon can occur from carbohydrates to fatty acids, the reverse (at least, in animal cells) is not possible.

Question 7

Regarding electrical signalling by graded potentials: Graded potentials are followed by a refractory period

Answer 7

FALSE

-Unlike action potentials, there is no concept of a refractory period for a graded potential.

Question 8

Concerning neurones. The main site of neurotransmitter release is the dendrite.

Answer 8

FALSE
-The main site of transmitter release is the presynaptic terminal. The dendrites are the main site for receiving information via synapses from other neurones. Neurotransmitter released from the presynaptic terminal evokes a postsynaptic potential (EPSP or IPSP) in the membrane of the dendrite. The sum of these potentials decides whether the cell will reach threshold and fire an action potential or not.

Question 9

Regarding basic pharmacology: The amino-acid sequence of G-protein coupled receptors has seven membrane spanning domains.

Answer 9

TRUE
-This is the family of metabotropic receptors. They are all built along the same lines and consist of a single amino acid sequence, which contains seven domains of lipophylic amino-acids that cross the cell membrane.

Question 10

Glutamine synthase catalyses the synthesis of glutamine from a-ketoglutarate and ammonium ion.

Answer 10

FALSE
-Glutamine synthase catalyses the synthesis of glutamine from glutamate and ammonium ion. When α-ketoglutarate and ammonium ion interact (a process catalysed by glutamate dehydrogenase), the product is glutamate (and water).

Question 11

Other than chylomicrons, low-density lipoproteins are the major transport system for triacylglycerols in the plasma.

Answer 11

FALSE

-The function of LDL particles is the transport of free cholesterol to peripheral tissues.

Question 12

The primary function of epithelia is to cover surfaces.

Answer 12

TRUE

-However most epithelia have one or more “secondary” functions.

Question 13

Tight junctions provide a strong bond between adjacent cells in an epithelial layer.

Answer 13

FALSE
-Desmosomes provide a strong bond between adjacent cells in an epithelial layer, tight junctions seal the gap between adjacent cells.

Question 14

Action potentials: Rely on the activity of voltage-gated Na+ channels.

Answer 14

TRUE
-Voltage-gated channels are triggered to open by depolarisation of the membrane to threshold. Once opened, these allow Na+ to flow in down its electrochemical gradient into the cell to cause the massive and sudden depolarisation of the cell.

Question 15

With regard to membrane potentials: The Nernst equation predicts the equilibrium potential for a single ion species.

Answer 15

TRUE
-Essentially, the Nernst equation says that the equilibrium potential for a particular ion depends on the concentrations of that ion inside and outside the cell. If you know these, you can predict what the equilibrium potential should be. Electrophysiologists find this very exciting. It is also of immediate relevance in explaining, for instance, the effect of increase plasma K+ concentration on the resting membrane potential.

Question 16

Transaminases require vitamin B2 as a cofactor.

Answer 16

FALSE
-Transaminases use as a cofactor pyridoxal phosphate, which is made from vitamin B6. (B2, incidentally, is riboflavin, essential in the diet for the production of FAD).

Question 17

Concerning skin: Tight junctions bind the cells of the epidermis together to give structural strength.

Answer 17

FALSE

-Desmosomes bind the cells of the epidermis together to give structural strength.

Question 18

In the zwitterion form, an amino-acid bears no charge.

Answer 18

FALSE
-The ‘zwitterion’ form of the amino-acid is the predominant molecular species present in aqueous solution at neutral pH values. In this form, both α-carboxyl and α-amino groups bear charge (as -COO- and -+NH3 respectively). This means that the amino-acid bears no net charge (unless the R group happens to be charged in this pH range).

Question 19

Hemidesmosomes attach epithelial cells to the basement membrane.

Answer 19

TRUE

-This forms part of the mechanism holding the epithelial cells onto the underlying connective tissue.

Question 20

Elimination of phenylalanine from the diet is a necessary treatment for a patient suffering from phenylketonuria.

Answer 20

FALSE
- Phenylketonuria results from a genetic defect in the enzyme which catalyses the hydroxylation of the amino-acid phenylalanine to produce another coded amino-acid, tyrosine. This causes high [plasma phenylalanine] and severe problems if untreated. Treatment involves restriction of dietary phenylalanine to amounts required for protein synthesis. Complete elimination of phenylalanine from the diet is not an option, since it is one of the essential amino-acids.

Question 21

Concerning skin: The ducts from eccrine sweat glands open onto the surface of the skin.

Answer 21

TRUE
-The ducts of eccrine (also known as merocrine) sweat glands open onto the surface of the skin, whereas those of apocrine sweat glands secrete into the hair follicle. Eccrine sweat glands are by far the most numerous and have a thermoregulatory function.

Question 22

Concerning enzymes: The presence of a non-competitive inhibitor does not alter the apparent Km (Michaelis constant) of an enzyme-catalysed reaction.

Answer 22

TRUE
-Non-competitive inhibitors essentially lower the concentration of active enzyme, by inactivating the enzyme. They therefore alter Vmax but generally have no effect on apparent Km.