Quiz 2 13/11/18

Question 1

In the α-helix, two amino-acids separated by four intervening amino-acids in the sequence are linked together.

Answer 1

FALSE
-There are 3 intervening amino-acids between the two interacting amino-acids. This was expressed in the lectures as a 1-5, 2-6, 3-7 etc bonding system.

Question 2

The Fe2+ ion in haemoglobin binds to the porphyrin ring of haem itself (four bonds), to the (α or β) polypeptide chain (one bond) and to diatomic oxygen (one bond).

Answer 2

TRUE

-The Fe2+ ion in haemoglobin has hexavalency, and binds as indicated in the statement.

Question 3

Adult human haemoglobin contains four polypeptides and one haem group, to which oxygen binds.

Answer 3

FALSE

-Haemoglobin contains four polypeptides and four haem groups, to each of which a molecule of oxygen can bind.

Question 4

The greater the number of double bonds in a fatty acid, the less soluble it is in water.

Answer 4

FALSE

-Haemoglobin contains four polypeptides and four haem groups, to each of which a molecule of oxygen can bind.

Question 5

In endocrine glands, the blood capillaries are lined by simple squamous epithelial cells with fenestrae.

Answer 5

TRUE

-The fenestrae allow for the easy passage of hormones from the secretory cells into the blood stream.

Question 6

Concerning neurones: Motor neurones exit the spinal cord via the ventral root.

Answer 6

TRUE

-Fine and handy since the cell bodies of the motor neurones are located in the ventral horn of the spinal cord.

Question 7

Action potentials: Are followed by a period where the membrane is less excitable.

Answer 7

TRUE
-The absolute and relative refractory periods occur because after the voltage–gated channels have opened they undergo a brief period of inactivation. They cannot be activated again until the membrane has repolarised and the channel been “reset”.

Question 8

Regarding basic pharmacology: A partial agonist is a drug that only activates specific sub-types of receptor.

Answer 8

FALSE
-A partial agonist is a drug that binds to a receptor and activates it, but not fully. The effects of partial agonists can be confusing. On its own, a partial agonist will produce a small response, but in the presence of a full agonist, it will reduce the response.

Question 9

Concerning skin: The epidermis of the skin is composed of dense regular connective tissue.

Answer 9

FALSE

-The epidermis of the skin is composed of a stratified squamous keratinising epithelium.

Question 10

Concerning enzymes: The Michaelis constant (Km) of an enzyme-catalysed reaction is numerically equal to the substrate concentration when the initial reaction rate is equal to ½ Vmax (the maximal rate of the reaction).

Answer 10

TRUE
-Incorrect. Km (the Michaelis constant) is indeed numerically equal to the substrate concentration when the initial reaction rate is equal to half Vmax. Carrying out experiments in which initial reaction rates occurring when different substrate concentrations are mixed with the same concentration of enzyme generates results that allow Vmax and Km to be estimated. The value of Km, under particular circumstances, is an indication of the affinity of an enzyme and substrate for one another.

Question 11

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

Answer 11

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

Question 12

Hemidesmosomes attach epithelial cells to the basement membrane.

Answer 12

TRUE

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

Question 13

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

Answer 13

FALSE

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

Question 14

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

Answer 14

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 15

Transport of aspartate from muscle to liver allows muscle pyruvate to be reconverted into liver glucose.

Answer 15

FALSE
- It is alanine transport that accomplishes this. Alanine transport not only provides safe movement of skeletal muscle nitrogen through the plasma for excretion, it also effectively allows the carbons of muscle glycolysis-produced pyruvate to be moved to the liver, where they can be used in gluconeogenesis.

Question 16

Concerning enzymes: An enzyme decreases the net free energy change that occurs when reactants are converted to products in a spontaneous reaction.

Answer 16

FALSE
-Spontaneous reactions occur with a decrease in free energy. They are not instantaneous, because their progress involves movement through transition states. These have free energies higher than those of the reactants and products. An enzyme acts as a catalyst by lowering the free energy of activation (activation energy) of a spontaneous reaction that is already progressing (perhaps, because of the transition state barrier, very slowly) towards (but not necessarily to reach) an equilibrium. An enzyme does not alter the overall free energy change that occurs when reactants are converted to products.

Question 17

Plasma ketone body concentration increases during starvation.

Answer 17

TRUE
- During starvation, fats are mobilised and fatty acids derived from them catabolised by β-oxidation in liver cell mitochondria. The capacity of the citric acid cycle to catabolise the acetyl CoA is soon exceeded, especially since oxaloacetate needed for acetyl CoA entry into the cycle is also required, under these circumstances, for gluconeogenesis. Excess acetyl CoA is therefore metabolised into ketone bodies, and these water-soluble molecules moved into plasma to act as fuel for many parts of the body.

Question 18

The primary function of epithelia is to cover surfaces.

Answer 18

TRUE

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

Question 19

Glutamate is one of the 20 genetically coded amino-acids.

Answer 19

TRUE
- ‘This genetically coded amino-acid plays a central role in the transfer of nitrogen atoms into and out of the biosphere, and, within the biosphere, in transferring N atoms to, between and from amino-acids. It has the R group -(CH2)2COO-.

Question 20

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

Answer 20

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 21

Concerning synaptic transmission and synaptic integration in the central nervous system: Autoreceptors are located on the presynaptic terminals of neurones.

Answer 21

TRUE
-Autoreceptors bind the same transmitter that the terminal releases. They are often of the g-protein coupled family and are ideally placed to perform a negative feedback role by inhibiting further release of transmitter.

Question 22

Ornithine and citrulline are non-coded, amino-acid intermediates of the urea cycle,

Answer 22

TRUE

-These molecules have the general structure of amino-acids, but are not among the 20 genetically coded molecules.