PGMEE Biochemistry MCQs 261-270

Q-261. Sphingomyelinase deficiency is seen in
a) Niemann – pick disease
b) Farber’s disease
c) Tay Sach’s disease
d) Krabbe’s disease

Answer: Niemann – pick disease
Niemann Pick disease:
Sphingomyelinase deficiency
Presence of foam cells or vacuolated cells
Important point:
Foam cells are seen in Niemann Pick disease, fucosidosis, beta mannosidosis etc.

Q-262. Which of the following lipoproteins does not move towards charged end in electrophoresis?
b) LDL
c) HDL
d) Chylomicrons

Answer: Chylomicrons
Classification of Lipoprotein on electrophoretic mobility:
HDL: Alpha-1 region
LDL: Beta region
VLDL: Pre-beta region
Chylomicron: Do not migrate

Q-263. Method of chromatography in which molecules that are negatively charged are selectively released form stationary phase into the positively charged molecules in mobile phase is termed as:
a) Affinity chromatography
b) Ion – Exchange chromatography
c) Absorption chromatography
d) Size-Exclusion chromatography

Answer: Ion – Exchange chromatography
Ion-exchange chromatography separates ions and polar molecules based on their affinity to the ion exchanger.

Q-264. Which of the following liver enzymes is predominantly mitochondrial?
c) GGT
d) 5’Nucleotidase

Answer: SGOT (AST)
Liver enzymes:
Cytosolic: SGPT, SGOT (Cytosolic iso-enzyme), LDL
Mitochondrial: SGOT (Mitochondrial iso-enzyme) and glutamate dehydrogenase (GDH)
Membrane bound: Alkaline phosphatase, GGT, 5’ Nucleotidase

Q-265. Which of following techniques is used for detection of variations in DNA sequence and gene expression?
a) Northern blot
b) Southern blot
c) Western blot
d) Microarray

Answer: Microarray
Microarray allows the detection of variations in DNA sequences, and enables description of gene expression.
Microarray technique is the most powerful tool for screening gene expression profile of biological sample.

Q-266. Which of the following tests is not used for detection of specific aneuploidy?
d) Microarray

Answer: Microarray
Detection of specific chromosomal aneuploidy:

Q-267. Prenatal diagnosis of hemophilia is best done by
a) PCR
b) Linkage analysis
c) Cytometry
d) Microarray

Answer: PCR
Prenatal diagnosis of hemophilia: Sampling
Chorionic villus sampling: Carried out after 11 weeks gestation to obtain DNA for analysis
Amniocentesis: Done after 16 weeks
Fetal blood sampling: Carried out at 18 weeks or more gestation
Important point:
Prenatal diagnosis of hemophilia is best done by direct mutation analysis using PCR technique.

Q-267. Thiamine deficiency causes decreased energy production because?
a) It is required for the process of transamination
b) It is co-factor in oxidative reduction
c) It is co-enzyme for trans-ketolase in pentose phosphate pathway
d) It is co-enzyme for pyruvate dehydrogenase & alpha ketoglutarate dehydrogenase

Answer: It is co-enzyme for pyruvate dehydrogenase & alpha ketoglutarate dehydrogenase
Thiamine has a central role in energy yielding metabolism, and especially the metabolism of carbohydrates.
Thiamine diphosphate is the coenzyme for three multi-enzyme complexes that catalyze oxidative decarboxylation reactions:
Pyruvate dehydrogenase in carbohydrate metabolism
Alpha keto-glutarate dehydrogenase in Citric Acid Cycle
Branched chain keto-acid dehydrogenase involved in the metabolism of leucine, iso-leucine and valine
Important points:
Thiamine diphosphate is also the coenzyme for trans-ketolase on PPP.
Thiamine trisphosphate has a role in nerve conduction; it phosphorylates, and so activates a chloride channel in the nerve membrane.

Q-268. What factor is responsible for deciding whether an antibody will remain membrane bound, or get secreted?
a) Carbohydrate content
b) Class switching
c) Differential RNA splicing
d) Surface charge

Answer: Differential RNA splicing
Differential RNA processing explains the progression from membrane-bound to secreted antibody.
Production of two forms of immuno-globins occurs by differential transcription of the germline C region of each heavy chain.
Membrane bound immuno-globin is identical to secreted immuno-globin except for an extra stretch of amino acids at C terminus of each heavy chain.
Their additional amino acids transverse the cell membrane and anchor the molecule in lipid bilayer.

Q-269. Vitamin K is involved in the post translational modification of?
a) Glutamate
b) Aspartate
c) Tyrosine
d) Tryptophan

Answer: Glutamate
Gamma-glutamyl carboxylase is an enzyme that catalyzes the posttranslational modification of vitamin K-dependent proteins.
Vitamin K is involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxy-glutamate (Gla) residues.
The modified residues are often situated within specific protein domains called Gla domains.
Gla residues are usually involved in binding calcium, and are essential for the biological activity of all known Gla proteins.
Proteins with Gla domains play key roles in the regulation of following physiological processes:
Blood coagulation: Prothrombin (factor II), factors VII, IX, and X, and proteins C, and S
Bone metabolism: Osteocalcin, also called bone Gla protein (BGP), matrix Gla protein (MGP), periostin, and the recently discovered Gla-rich protein (GRP).
Important point:
Osteocalcin also contains hydroxy-proline, so its synthesis is dependent on both Vitamin K and C; in addition, its synthesis is induced by vitamin D.

Q-270. Which among the following is not a cause of fasting hypoglycemia?
a) Glucagon excess
b) Glucose-6-phosphatase deficiency
c) Cirrhotic liver damage
d) Glycogen synthase deficiency

Answer: Glucagon excess
Common causes of fasting Hypoglycemia:
Pancreatic B cell tumor
Surreptitious administration of insulin or sulfonylurea
Extra-pancreatic tumors
Addison disease
Acute alcoholism or liver failure
End stage of CKD (Chronic kidney disease)
Important point:
When blood glucose begins to fall, glucagon signals the liver to break down glycogen and release glucose into the bloodstream.
In some people with diabetes, this glucagon response to hypoglycemia is impaired and other hormones such as epinephrine may raise the blood glucose level.
Glucagon injection rapidly brings the blood glucose level back to normal and help the person regain consciousness in Type I DM.