Tuesday, November 13, 2012

GATE Questions: Biochemistry

 1. Which of the following inhibitor uncouples electron transport and oxidative phosphorylation?
(a) Azide
(b) Dinitrophenol (DNP)
(d) Rotenone
Ans: Dinitrophenol (DNP)
  • Azide  (N3-), cyanide (CN-) and CO all inhibit cytochrome oxidase
  • DNP is an un coupling agent as they stop ATP synthesis without disrupting electron transport.  Here the energy derived from electron transport is released as heat.
  • Rotenone and amytal inhibits electron transport at NADH dehydrogenase 
  • Uncoupling protein thermogenin in brown adipose tissue for maintaining body temperature in cold thriving animals
  • Non shivering thermogenesis: The production of heat by uncoupling
2. Which of the following activate Protein kinace C
(a) Inositol 1,4,5-triphosphate
(b) Diacylglycerol
(d)Cyclic AMP
Ans: Inositol 1,4,5-triphosphate (IP3)
  • All options are intracellular signalling molecules called second messengers
3. Transcription initiation sites can be determined by
(a) Foot Printing
(b) Northern Blotting
(c) Primer extension
(d) Nick translation
Ans: Foot Printing
  • DNA foot printing: The identification of protein binding site on a DNA molecule Here RNA polymerase enzyme (a protein) binds to the transcription initiation site at the beginning of transcription.
  • Northern Blotting: identifying specific RNA sequence in a sample using a probe
  • Primer extension: by DNA polymerase
  • Nick translation: The repair of nick (ss breaks) using DNA pol I, generally to introduce labelled nucleotides into a DNA molecule
4. One common feature between B and T cells is that
(a) both cells produce antibodies
(b) both cells possess MHC class II
(c) both B cell receptor and T cell receptor undergo rearrangement
(d) both cells can produce cytokines
Ans:  both B cell receptor and T cell receptor undergo rearrangement
  • Only B cell can produce antibodies (specifically plasma cells)
  •  Only B cells possess MHC class II as it can also function as antigen presenting cells
  • Only T cell can produce cytokines that eventually activates B cells
5. In Hybridoma technology, the myeloma cells used
(a) lack HGPRTase
(b) lack the ability to produce Ig
(c) lack both HGPRTase and ability to produce Ig
(d) lack thymidine kinase
Ans: lack HGPRTase
  • Myeloma cells will die out in HAT selection medium as it lacks HGPRTase (enzyme in nucleotide synthesis) and B cells will undergo normal cell death and only hybrid cells survive in HAT medium (refer monoclonal antibody production)                                   
6. Which amino acid residue is most likely to be found in the interior of a water soluble globular protein?
a) Ser
b) Arg
c) Asp
d) Val
Ans: Valine: A hydrophobic amino acid preferring interior of the globular protein
  • Arginine and asparagine are hydrophilic and tend to be in the exterior, serine is also reactive due to the presence of OH group (polar).
7.  Of the peptide sequences given below, which one is the digestive enzyme trypsin most likely to cleave?
a) ----Val-Lys-Pro-Met----
b) ----Arg-Val-Phe-Tyr----
c) ----Glu-Gly-Trp-Gly----
d) ----Trp-Asp-Gln-Pro---- 

Ans: b) ----Arg-Val-Phe-Tyr----
  • Digestive enzyme Trypsin cleave on the C terminal side of basic amino acids (Arg, Lys) residues
  • Chymotrypsin cleave on the C terminal side of aromatic amino acids (Phe, Trp, Tyr) residues
  • Cyanogen bromide cleave C terminal side of Met residues
8. Which pair of amino acids will have the highest absorbance at 280 nm? (Assume equimolar concentarions)
a) Thr & His
b) Phe & Pro
c) Trp &Tyr
d) Phe & His
Ans: c) Trp &Tyr
  • Absorbance at 280nm is by aromatic amino acids. Here Tryptophan and tyrosine are the aromatic amino acids (Phe is the other aromatic amino acid)
  • Order of absorbance: Trp>Tyr>Phe
  • The aromatic rings of Trp and Tyr contain delocalised π electrons that strongly absorb UV light (280nm).
9. Vitamin D is derived from which of the following precursors by the action of UV-light?
a) 7-Dehyrocholestrol
b) Lanosterol
c) Glycocholate
d) Squalene epoxide
Ans: a) 7-Dehyrocholestrol
  • Vit-D (Cholecalciferol)
For more, refer our post: Vitamins

10. The molecular defect in familial hypercholesterolemia is due to the lack of functional
a) VLDL receptor
b) IDL receptor
c) LDL receptor
d) HDL receptor
Ans: c) LDL receptor
  • Familial hypercholesterolemia an inherited disorder 
  • Condition: elevated level of cholesterol in the blood as LDL cholesterol cannot be taken up by the tissues.
------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------
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