Test 91    (biochemistry)

1. Purines:

a. include guanine

b. are metabolized to uric acid

c. are mainly synthesized in the liver

d. are used in the formation of ATPs

e. are made from amino acids

Answera.T   b.T  c.T  d.T  e.T
Adenine and guanine are purines.
They are essential for the formation of nuclei acids, coenzymes and ATPs

2. Vitamin B12:

a. is a fat soluble protein

b. is essential for the metabolism of folic acid in 
    the humans

c. is attached to a glycoprotein in the circulation

d. its deficiency is characterized by hypersegmentation
    of the neutrophils

e. its deficiency causes blindness

Answera.F   b.T   c.T  d.T  e.T
Vitamin B12 is a water soluble vitamin.
Its deficiency is associated with poor maturation 
of the nucleus which is manifested by the presence
of hypersegmented nuclei seen in neutrophils.
Subacute combined degeneration of the cord is
a feature of severe vitamin B12 deficiency and optic atrophy can occur.

3. Ascorbic acids:

a. are present in high concentration in the adrenal cortex
    and the eye.

b. stress reduces the body concentration of ascorbic acids

c. excessive amount leads to the formation of oxalate 
    stones in the urinary tracts

d. are heat-labile

e. are present in higher concentration in the aqueous than
    in the circulation.

Answera.T   b.T  c.T  d.T  e.T
Stress and glucocorticoids both endogenous and 
exogenous lead to loss of ascorbic acids from the adrenal cortex and supplement is required to avoid poor wound healing.
Excessive vitamin C is associated with deposition of oxalate stones in the urinary tracts.
.

4. Folic acid:

a. is water soluble

b. is absorbed in the stomach

c. deficiency leads to aplastic anaemia

d. deficiency occurs with methatrexate treatment

e. deficiency is associated with risk of neural tube defect
    in the newborn.

Answera.T   b.F   c.F   d.F  e.T
Methatrexate, an antimetabolite binds competitively
to the enzyme dihydrofolate reductase and block the 
conversion of folic acid to tetrahydrofolates essential for biosynthesis of purines and pyrimidines.
In order to overcome this problem, excess folic acid is given to reduce the side-effects.
Folic acid as in vitamin B12 deficiency give rise to macrocytic anaemia.

5. Prostaglandins:

a. contains 20 carbon atoms

b. are unsaturated fatty acids containing a cyclopentane 
    ring

c. are metabolized in the lungs

d. the different types of prostaglandins are classified
    according to the configuration of the cyclopentane ring

e. have a biological half-life of about 24 hours.

Answera.T   b.T  c.F  d.T  e.F
Prostaglandins have very short half-life for example 
prostacyclin is about 3 minutes and thromboxane about 30 seconds.

 
 

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