Q-131. Which one of the following amino acids is most likely to be found in the trans-membrane region of a protein?
a) Lysine
b) Arginine
c) Leucine
d) Aspartate
Answer: Leucine
Explanation:
Proteins tend to fold with the R- groups of amino acids with hydrophobic side chains in the interior.
Amino acids with charged or polar amino acids side chains (arginine, glutamine, and serine) generally are present on the surface.
Amino Acids with Aliphatic or Non-Polar Side Chains are Glycine, Alanine, Valine, Leucine and Iso-Leucine.
Q-132. Molecular weight of a protein can be determined by
a) Native Poly Acryl-amide Gel Electrophoresis (PAGE)
b) Sodium Dodecyl Sulfate PAGE
c) Iso-electric focusing
d) Ion Exchange Chromatography
Answer: Sodium Dodecyl Sulfate PAGE
Explanation:
The most widely used method for determining the purity of a protein is SDS – PAGE in the presence of the anionic detergent sodium dodecyl sulfate (SDS). Electrophoresis separates charged bio-molecules based on the rates at which they migrate in an applied electrical field.
Since the charge-to-mass ratio of each SDS polypeptide complex is approximately equal, the physical resistance each peptide encounters as it moves through the acryl-amide matrix determines the rate of migration.
Since large complexes encounter greater resistance, polypeptides separate based on their relative molecular mass (M), Individual polypeptides trapped in the acryl-amide gel are visualized by staining with dyes such as Coomassie blue.
Q-133. Membrane fluidity is increased by
a) Stearic acid
b) Palmitic acid
c) Cholesterol
d) Linoleic acid
Answer: Linoleic acid
Explanation:
Lipids with shorter chains are less stiff and less viscous because they are more susceptible to changes in kinetic energy due to their smaller molecular size and they have less surface area to undergo stabilizing van der Waals interactions with neighboring hydrophobic chains.
Lipid chains with double bonds are more fluid than lipids that are saturated with hydrogen and thus have only single bonds. On the molecular level, unsaturated double bonds make it harder for the lipids to pack together by putting kinks into the otherwise straightened hydrocarbon chain.
Examples of unsaturated fats are palmitoleic acid, oleic acid, linoleic acid, and arachidonic acid.
Cholesterol acts as a bidirectional regulator of membrane fluidity because at high temperatures, it stabilizes the membrane and raises its melting point, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together and stiffening.
Q-134. The molecule, which is the initiator of cataract formation in the eye lens and whose 1-phosphate derivative is responsible for liver failure is:
a) Sorbitol
b) Mannitol
c) Inositol
d) Galactitol
Answer: Galactitol
Explanation:
Galactose 1 phosphate uridyl-transferase is missing in individuals with classical Galactosemia.
Galactose 1 phosphate and therefore Galactose accumulate in cells.
Accumulated Galactose is shunted into side-pathways such as that of Galactitol production.
This reaction is catalyzed by aldose reductase, same enzyme that converts glucose to sorbitol.
More benign form of Galactosemia is caused by a deficiency of galactokinase.
Classical Galactosemia:
Uridyl-transferase deficiency
Autosomal recessive disorder
It causes Galactosemia and galactosuria, vomiting, diarrhoea and jaundice.
Accumulation of Galactose 1 phosphate and Galactitol in nerve, lens, liver and kidney tissue causes liver damage, severe mental retardation and cataracts.
Antenatal diagnosis is possible by chorionic villus sampling.
Therapy: Rapid removal Galactose i.e. lactose from the diet.
Q-135. What is most accurate effect of smoking cessation?
a) Shift of oxy-hemoglobin curve to the right
b) Increased ciliary function
c) Decreased mucous production
d) Decreased incidence of post operative pneumonia
Answer: Shift of oxy-hemoglobin curve to the right
Explanation:
Smoking causes an increase in carboxy-hemoglobin levels, resulting in a leftward shift.
There are two mechanisms responsible for the leftward shift of oxy-hemoglobin dissociation curve when carbon monoxide is present in the blood.
Carbon monoxide has a direct effect on oxy-hemoglobin, causing a leftward shift of the oxygen dissociation curve, and carbon monoxide also reduces the formation of 2, 3-DPG by inhibiting glycolysis in the erythrocyte.
Q-136. At physiological pH, the carboxy- terminal of a peptide is
a) Positively charged
b) Negatively charged
c) Neutral
d) Infinitely charged
Answer: Negatively charged
Explanation:
At physiological pH, all amino acids have both a negatively charged group, carboxyl ion and a positively charged group ammonium ion.
Q-137. Apart from occurring in nucleic acids, Pyrimidines are also found in:
a) Theophylline
b) Theobromine
c) Flavin mononucleotide
d) Thiamine
Answer: Thiamine
Explanation:
The pyrimidine ring system has wide occurrence in nature as substituted and ring fused compounds and derivatives, including the nucleotides, thiamine (vitamin B-1) and alloxan.
It is also found in many synthetic compounds such as barbiturates and the HIV drug, zidovudine.
Q-138. By which of the following anticoagulants used in estimating blood glucose, glycolysis is prevented:
a) EDTA
b) Heparin
c) Sodium fluoride
d) Sodium citrate
Answer: Sodium fluoride
Explanation:
Fluoride inhibits glycolysis by inhibiting enolase; this will help in correct determination of the glucose level as glycolysis will not be able to affect the level of glucose.
Q-139. Which of the following is a component of the visual pigment Rhodopsin?
a) b-carotene
b) Retinal
c) Retinol
d) Retinoic acid
Answer: Retinal
Explanation:
The retinoids are related to retinol (Vitamin A) are essential for vision, reproduction, growth and maintenance of epithelial tissues.
Retinoic acid derived from oxidation of dietary retinol, mediates most of the action of the retinoids except for vision, which depends on retinal (Retinal-aldehyde), the aldehyde derivative of retinol.
Q-140. Vitamin A is stored mainly as retinol esters in:
a) Kidney
b) Muscle
c) Liver
d) Retina
Answer: Liver
Explanation:
Retinol esters present in the diet are hydrolyzed in the intestinal mucosa, releasing retinol and free fatty acids.
Retinol is re-esterified to long chain fatty acids in the intestinal mucosa and secreted as a component of chylomicrons into the lymphatics system.
Retinol esters contained in chylomicrons are taken up by and stored in the liver.