Quiz 2 true or false

Question 1

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

Answer 1

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 2

‘Lipases’ is the general name for enzymes concerned with the synthesis of lipids (fats)

Answer 2

FALSE
-Lipases are enzymes that catalyse the hydrolysis of the ester links between fatty acids and glycerol. Hence, the function of several such enzymes is the release of fatty acids from triacylglycerols. The fatty acids so ‘mobilised’ can then be metabolised.

Question 3

A simple epithelium is one which contains cells of only one type

Answer 3

FALSE

-A simple epithelium contains only one layer of cells- those cells may be of the same or of different types.

Question 4

Action potentials: Encode stimulus intensity in their amplitude

Answer 4

FALSE

-They are all or none and can therefore encode stimulus intensity only in their frequency.

Question 5

Regarding electrical signalling by graded potentials: Graded potentials are only suited to signalling over short distances.

Answer 5

TRUE
-Graded (or decremental) potentials quickly decay as they travel along the membrane. To conduct electrical signals over any decent distance requires the use of a self-propagating action potential.

Question 6

When glutamate reacts with pyruvate, α-ketoglutarate and alanine are produced

Answer 6

TRUE
-The reaction described is a transamination. The α-amino-acid glutamate is converted into its corresponding α-keto-acid α-ketoglutarate, and the α-keto-acid pyruvate is converted into its corresponding α-amino-acid alanine.

Question 7

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

Answer 7

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 8

Regarding basic pharmacology: A second-messenger is chemical signal released from the presynaptic terminal after the orthodox neurotransmitter.

Answer 8

FALSE
-A second messenger is produced by an enzyme inside a cell following activation of cell-surface receptors by a neurotransmitter or hormone. The principle examples are cAMP, which is produced by adenylyl cyclase, and IP3 and DAG, which are produced by phospholipase C.

Question 9

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

Answer 9

FALSE

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

Question 10

Aspirin acts by inhibiting an enzyme concerned in the synthesis of leukotrienes.

Answer 10

FALSE
- Arachidonic acid is converted into prostaglandins and thromboxanes by one pathway, and into leukotrienes by another. The enzyme inhibited by aspirin participates in the former pathway.

Question 11

Pseudostratified columnar epithelia have two to three layers of cells with only the basal layer of cells attached to the basement membrane.

Answer 11

FALSE
-Pseudostratified columnar epithelia only appear to have two to three layers of cells but all the cells are attached to the basement membrane.

Question 12

Concerning neurones. Interneurones do not fire action potentials.

Answer 12

FALSE
-The distinguishing feature of interneurones is that they lie entirely within the central nervous system; apart from that, they follow all the rules that other neurones do.

Question 13

Regarding basic pharmacology: Receptors associated with JAK kinases have the intrinsic ability to phosphorylate a substrate.

Answer 13

FALSE
-This type of receptor has no enzymic activity itself. Instead, agonist binding to the receptor causes a conformational change that causes activation of an associated protein, the JAK kinase. Compare this with the receptor tyrosine kinases, which have their own intrinsic enzymic activity, and the G-protein coupled receptors, which must use a G-protein middle-man to regulate activity of a separate enzyme.

Question 14

The body tends to move into positive nitrogen balance during pregnancy

Answer 14

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 15

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

Answer 15

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 16

Concerning enzymes: The binding of an allosteric inhibitor to an enzyme is usually irreversible.

Answer 16

FALSE

-The binding is reversible. Remember that regulation needs to be rapid and reversible.

Question 17

Sickle-cell haemoglobin, in solution at pH 7, has a greater negative charge than does normal haemoglobin.

Answer 17

FALSE
-Since the mutation to produce sickle-cell haemoglobin causes the protein to be made with valine (an amino-acid with an uncharged R group) in a place normally occupied by glutamate (an amino-acid with a negative charge at pH 7), the mutant protein has a lesser negative charge than does normal haemoglobin.

Question 18

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

Answer 18

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 19

Regarding basic pharmacology: Each neurotransmitter typically acts on a single type of receptor.

Answer 19

FALSE

-Most neurotransmitters can act on several different receptors, producing a variety of effects.

Question 20

Metabolism of nitrogen into and through the urea cycle is accompanied by ATP synthesis.

Answer 20

FALSE
-Dephosphorylation of ATP (not its synthesis) occurs during metabolism through the urea cycle. The formation of carbamoyl phosphate from ammonium ion and carbon dioxide requires dephosphorylation of 2 ATP to produce ADP, and the conversion of citrulline to arginosuccinate during the cycle requires conversion of ATP to AMP. So, production of urea for excretion requires an input of energy.

Question 21

Regarding electrical signalling by graded potentials: Graded potentials have no threshold.

Answer 21

TRUE
-Action potentials are generated by voltage-gated channels, which must be depolarised to threshold for them to open. Graded potentials (for example an EPSP generated by a ligand-gated channel) do not require any voltage threshold to be reached.

Question 22

In liver, glutaminase catalyses the conversion of glutamate to glutamine.

Answer 22

FALSE
-Glutaminase catalyses the conversion of glutamine to glutamate. Plasma glutamine arises from the addition, in tissues, of ammonium ion to glutamate (in the glutamine synthase-catalysed reaction), so that nitrogen can be conveniently and safely transported from tissues to the liver for (eventual) excretion. On arrival, glutamine is reconverted to glutamate and ammonium ion. This process is catalysed by the liver enzyme glutaminase.

Question
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Question 23

Concerning enzymes: Isoenzymes (isozymes) are enzymes that catalyse more than one chemical reaction.

Answer 23

FALSE
-Isoenzymes are enzymes differing in their primary structure but catalysing the same reaction or set of reactions. Examples are the glucokinase and hexokinase enzymes, both of which catalyse conversion of glucose to glucose 6-phosphate, the different forms of lactate dehydrogenase and of creatine kinase.