Sunday, October 18, 2009

37 - Biochemical reactions of Folate coenzymes

Coenzyme Form of Folate Involved and Single Carbon unit transferred
Formate activation
THF; -CHO group transferred.
Generation of 10-formyl-THF
Purine synthesis

Formation of glycinamide ribonucleotide
5,10-MethyleneTHF; -CHO group transferred
Formation of purines needed
for DNA, RNA synthesis, but reactions 
probably not rate limiting
Formylation of aminoimidazolecarboxamide-ribonucleotide (AICAR)
10-Formyl (CHO)THF;-CHO group transferred
Pyrimidine synthesis

Methylation of deoxyuridine monophosphate (dUMP) to thymidine monophosphate (dTMP)
5,10-MethyleneTHF;-CH3 group transferred.
Rate limiting in DNA synthesis
Oxidizes THF to DHF
Some breakdown
of folate at the C-9–N-10 bond
Amino acid interconversion

Serine–glycine interconversion
THF; =CH2 group transferred
Entry of single carbon units into active pool
Homocysteine to methionine
5-Methyl(M)THF; -CH3 group transferred
Demethylation of 5-MTHF to THF; also requires cobalamin, flavine adenine dinucleotide, ATP, and adenosyl
Forminoglutamic acid to glutamic acid in histidine catabolism
THF; -HN-CH= group transferred

Wednesday, September 16, 2009

36 - Diseases caused by mutations in collagen genes

Diseases Caused by Mutations in Collagen Genes or by Deficiencies in the Activities of Posttranslational Enzymes Involved in the Biosynthesis of Collagen.
Gene or Enzyme Disease
COL1A1, COL1A2  Osteogenesis imperfecta, type 1 (MIM 166200)
Osteoporosis (MIM 166710)
Ehlers-Danlos syndrome type VII autosomal dominant (130060)
COL2A1  Severe chondrodysplasias
Osteoarthritis (MIM 165720)
COL3A1  Ehlers-Danlos syndrome type IV (MIM 130050)
COL4A3–COL4A6  Alport syndrome (including both autosomal and X-linked forms) (MIM 104200)
COL7A1  Epidermolysis bullosa, dystrophic (MIM 131750)
COL10A1  Schmid metaphysial chondrodysplasia (MIM 156500)
Lysyl hydroxylase Ehlers-Danlos syndrome type VI (MIM 225400)
Procollagen N-proteinase  Ehlers-Danlos syndrome type VII autosomal recessive (MIM 225410)
Lysyl hydroxylase Menkes disease (MIM 309400)

Sunday, April 26, 2009

35 - AIIMS MAY 2001 biochemistry mcqs with answers

1q) Vitamin K is needed for the post translational
modification of

a) Carboxylation
b) Methylation
c) Hydroxylation
d) Transketolation

2q) Amber codon refers to

a) Initiating codon
b) Mutant codon
c) Stop codon
d) Codon coding for multiple amino acids

3q) At physiological pH, the most stable amino
acid is

a) Histidine
b) Lysine
c) Arginine
d) Leucine

4q) In cystinuria, amino acids excreted are all the
following except:

a) Ornithine
b) Arginine
c) Lysine
d) Histidine

5q) Dietary triglycerides are transported by

a) Chylomicrons
b) LDL
d) HDL

6q) In which of the following reaction, thiamine
is not used

a) Alpha ketoglutarate to succinyl CoA
b) Glucose to pentose
c) Oxidative decarboxylation of Alpha keto amino acids
d) Lactate to pyruvate

7q) In chromatography, mass movement of the
substances is seen in

a) Electrophoresis
b) Diffusion
c) Osmosis
d) Paper chromatography

8q) The type of chromatography in which
proteins are bound to another substance is

a) Hydrophobic chromatography
b) Affinity chromatography
c) paper chromatography
d) gel chromatography

9q) The end-product of citric acid cycle used in
detoxification of ammonia in brain is

a) Oxaloacetate
b) Alpha keto glutarate
c) Succinate
d) Citrate

Tuesday, March 31, 2009

34 - AIIMS november 2002 biochemistry mcqs

1q: an alfa helix of a protein is most likely to be disrupted if a missense mutation introduces the following aminoacid with in the alpha helical structure ?

a. alanine
b. aspartic acid
c. tyrosine
d. glycine

explanation : alfa helix of a protein can be disrupted due to the introduction of the following aminoacids :

1. proline : the imino group of proline is not geometrically compatible with the right handed spiral of the alpha-helix

2. charged aminoacids : glutamate ,aspartate, lysine, arginine and histidine .

3. aminoacids with bulky side chains : tryptophan

4. aminoacids that branch at the beta-carbon : valine and isoleucine .

Subscribe Now: Feed

You are visitor number

Visitors currently online