PGMEE Biochemistry MCQs 271-280

Q-271. Cell fusion is an innovative method of preparing specific antibody technique to induce cell fusion includes following all except?
a) Attaching inactive viral particle on cell membrane
b) Adding ethylene glycol
c) Applying a small electric current
d) Reducing the viscosity of the membrane

Answer: Reducing the viscosity of the membrane
Explanation:
During the fusion process, B cells are isolated from the mouse spleen previously injected with an antigen, mixed with the mouse myeloma cell line and fusion is induced with polyethylene glycol (PEG).
The resulting hybridomas are then cultured in tissue culture medium containing hypo-xanthine, aminopterin, and thymidine (HAT).
Hybridoma multiplies and myeloma and B cells die.
Important point:
Hybridomas provide long term sources of highly useful monoclonal (Mono-specific) antibodies.

Q-272. Urea cycle occurs in:
a) Liver
b) Intestine
c) Brain
d) Kidney

Answer: Liver
Explanation:
Urea cycle occurs in liver and urea is produced. Urea is transported in the blood to kidneys for excretion in the urine.
The first two reactions leading to the synthesis of urea occur in the mitochondria, whereas the remaining cycle enzymes are located in cytosol.
Important points:
Synthesis of urea is irreversible.
Carbamoyl phosphate synthetase-I is rate limiting step in the urea cycle.
N-acetyl-glutamate is essential activator for carbamoyl phosphate synthetase-I.
Synthesis of one mol of urea requires 3 mol of ATP and one mol of ammonium ion.

Q-273. Which of the following change in a vector used to increase the yield of protein, produced in recombinant protein synthesis?
a) Inducible promoter
b) Genes for protease inhibitors
c) Translation initiation
d) Translation and transcription termination

Answer: Inducible promoter
Explanation:
Recombinant protein synthesis:
The recombinant gene is fused to a controllable promoter, which is activated by addition of an inducer to initiate transcription.
Overproduction of recombinant proteins is always a two-step process starting with a growth regimen to obtain a high cell density followed by the expression phase.

Q-274. Two transgenic plants are genetically engineered using recombinant DNA technology. One plant was transformed using a plasmid vector with Green Fluorescent Protein gene and other plant was transformed with fire fly luciferase gene. Which plant will glow in the dark?
a) Both plants will glow
b) Neither will glow
c) Plant expressing green fluorescent protein will glow
d) Plant expressing fire fly luciferase will glow

Answer: Plant expressing fire fly luciferase will glow
Explanation:
Bioluminescence is defined as the ability of living organisms to emit light through the chemiluminescence phenomenon.
The light emission is due to transfer of electrons from a substrate, in presence of an enzyme called Luciferase. The electrons are transferred to a lower energetic level, with an output of energy in the form of light radiation.
Among the animals, it can be found insects, shellfishes and molluscan.
Green Fluorescent Protein is a protein produced by a jellyfish Aequorea victoria; which produces glowing points of light around the margin of its umbrella.
The light arises from photogenic cells. These cells generate light by a process of bioluminescence, whose components include a calcium-activated photo-protein (Aequorin) that emits blue-green light and an accessory green fluorescent protein, which accepts energy from aequorin and re-emits it as green light. Green fluorescent protein will not glow in dark in absence of Aequorin.
Important points:
A few years back the bioluminescence phenomenon found application in the healthcare field, in particular in the fight against cancer.
The Bioluminescent activated destruction technique consists in the transformation of tumorigenic cells so that they express both the photo-sensibilizing and the luciferase gene from the firefly.
This way the cells, emitting bioluminescence, commit some sort of suicide because the photo-sensibilizing reacts to the luminescence producing toxins.

Q-275. A patient who was given primaquine develops hemolysis. The probable cause may be
a) Glucose 6 phosphate dehydrogenase deficiency
b) Glucose 6 phosphatase deficiency
c) Alpha keto glutarate dehydrogenase deficiency
d) Pyruvate Kinase Deficiency

Answer: Glucose 6 phosphate dehydrogenase deficiency
Explanation:
Glucose-6-phosphate dehydrogenase deficiency:
Impairment of the generation of NADPH
The gene is on the X chromosome, so it is mainly males who are affected.
Heterozygous condition confers resistance against malaria.
The defect is manifested as red cell hemolysis when susceptible individuals are subjected to oxidative stress from infections, drugs such as primaquine and sulfonamides or when they have eaten fava beans-hence the name of the disease, favism.

Q-276. Transfer of an amino group from an amino acid to an alpha keto acid is done by?
a) Transaminases
b) Aminases
c) Trans-ketolase
d) Decarboxylase

Answer: Transaminases
Explanation:
Transaminase or amino-transferase transfers alpha amino nitrogen to alpha ketoglutarate, forming glutamate in urea synthesis and also function in amino acid biosynthesis.
Alanine amino-transferase and glutamate amino-transferase catalyze the transfer of amino group to pyruvate forming alanine or to alpha keto-glutarate forming glutamate.
Important points:
The co-enzyme Pyridoxal phosphate (PLP) is present at catalytic site of amino-transferase.
During transamination, enzyme bound PLP serves as a carrier of amino groups.

Q-277. Which of the following statements about high density lipoprotein (HDL) is false-
a) HDL increases oxidation of LDL
b) HDL reduces foam cell production by LDL
c) HDL is best predictor of CAD
d) HDL helps to clear lipids from atheromas

Answer: HDL increases oxidation of LDL
Explanation:
HDL is synthesized and secreted from both liver and intestine.
However, apo-C and apo-E are synthesized in the liver and transferred from liver HDL to intestinal HDL when the later enters the plasma.
A major function of HDL is act as a repository for apo-C and apo-E required in the metabolism of chylomicrons and VLDL.
Reverse the cholesterol transport to liver for excretion via bile
HDL-2 concentrations are inversely related to the incidence of atherosclerosis.

Q-278. An immunoglobulin molecule represents the following level of organized protein structure
a) Primary structure
b) Secondary structure
c) Tertiary structure
d) Quaternary structure

Answer: Quaternary structure
Explanation:
Quaternary structure:
Represents the spatial arrangement of proteins that are made up of two or more peptide chains held together by non-covalent interactions or covalent cross links.
Quaternary structure includes:
Creatine kinase
Hemoglobin
Immunoglobulin
Lactase dehydrogenase

Q-279. All of the following metabolic occur in the mitochondria except
a) Beta-oxidation of fatty acids
b) Biosynthesis of fatty acids
c) Protein synthesis
d) Citric acid cycle

Answer: Biosynthesis of fatty acids
Explanation:
Metabolic functions occurring in mitochondria:
Citric acid cycle
Beta-oxidation of fatty acids
Electron transport chain
Ketone body formation
Oxidative phosphorylation
Important points:
Biosynthesis of fatty acids occurs in cytosol.
Mitochondria contain their own DNA, RNA and ribosomes; and synthesis of limited protein occurs in mitochondria.

Q-280. Which of the following events does not occur when concentration of glucose in the liver decreases
a) Inactivation of phospho-Fructo-kinase- 2 (PFK-2)
b) Activation of Fructose-2, 6 Bis-phosphatase
c) Increased levels of fructose 2, 6- bis-phosphate
d) Increased levels of glucagon

Answer: Increased levels of fructose 2, 6- bis-phosphate
Explanation:
Decreased Glucose-> Increased glucagon-> Increased c-AMP/Active protein kinase-A->Activation of fructose 2, 6 bis-phosphatase (Fructose bis-phosphatase-2) and inactivation of phospho-Fructo-kinase- 2-> Increased conversion of fructose 2, 6 bis-phosphate to fructose 6 phosphate-> Decreased concentration of fructose 2, 6 bis-phosphate-> Activate fructose bis-phosphatase-1-> Stimulates gluconeogenesis by forming more fructose 6 phosphate