Test 18 (Biochemistry)

1. With regard to histones:

a. they are basic proteins

b. they are essential for the formation of stable DNA

c. mitochondria do not contain histones

d. in the chromosomes, the weight of the histones equal to that of the 
    DNA

e. the amino acid composition of histones show great variability 
    amongst different human races

answera.T   b.T   c.T   d.T   e.F
Histones are basic protein which bind with DNA to form chromosomes - a stable structure.
They are absent in the mitochondria.
The amino acid composition of histones is highly conserved even between distantly related species.
 

2. In the regulation of genes:

a. more than 90% of the base sequences in human DNA have not 
    known function

b. extrons are the part of the gene that code for amino acids found in 
    the final proteins.

c. introns usually begins with the nucleotide sequence GT

d. splicing cut out the mRNA coded by introns.

e. promoters are responsible for initiating gene transcription

answera.T   b.T   c.T   d.F   e.T
In the gene, the extrons represent the expressed sequence of the DNA whereas introns the intervening sequences. Introns usually begin with the nucleotide sequence GT and end with AG.
 
 

3. Thromboxane A₂(TXA₂):

a. is derived from the membrane phospholipid

b. requires lipoxygenase for its production

c. its production is decreased by non-steroidal anti-inflammatory 
    drugs

d. causes platelet aggregation

e. causes vasodilatation

answera.T   b.F   c.T   d.T   e.F
It is formed from membrane phospholipid through the action of cyclo-oxygenase.
It causes platelet aggregation and vasoconstriction.
 

4. In the lens:

a. the capsule is made up of type IV collagen

b. most metabolism is carried out in the anterior pole

c. hexokinase is a rate-limiting enzyme in carbohydrate metabolism

d. anaerobic glycolysis is the main source of energy

e. pentose phosphate pathway metabolizes 30% of the available 
    glucose

answera.T   b.T   c.T   d.T   e.F
Epithelium is found in the anterior pole where metabolism is carried out.
Pentose phosphate pathway metabolizes 5% of the glucose in the lens.

a

5. The following are true about the oxidation of glucose:

a. glycolysis produces 3% of the energy ultimately obtained from 
    glucose

b. the first stage of glycolysis involves phosphorylation of glucose to 
    1,6-fructose biphosphate.

c. glycolysis occurs within the mitochondria

d. glucose enters the Kreb's cycle as pyruvate

e. the Kreb's cycle generates 36 ATP molecules.

answera.T   b.T    c.F   d.T   e.T
Complete oxidation of glucose usually involves two steps: glycolysis and the Krebs cycle.
Glycolysis yields 2 ATP molecules whereas the Krebs cycle yields 36 ATP molecules.