Friday, November 9, 2012

biochemistry MCQ



*1. Which of the following inhibitor uncouples electron transport and
oxidative phosphorylation?*
(a) Azide
(b) Dinitrophenol (DNP)
(c) Oligomycin
(d) Rotenone
Ans: Dinitrophenol (DNP)

  * Azide,cyanide 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
(c)Inositol
(d)Cyclic AMP
Ans: Inositol 1,4,5-triphosphate (IP_3 )

  * 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)

*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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