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  #1  
Old 04-10-2011
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DNA Base codons and template versus coding strands!

the base sequence of codons 57-58 in cytochrome b5 reductase gene is

CAGCGC

the mRNA produced will contain the codon sequence

ANSWER IS CAGCGC

HOW CAN WE ASSUME that it's coding strand or template strand?
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Old 04-10-2011
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Arrow Is this qn from NBME?

Strands and Directions of Synthesis

All strands are synthesized from the 5' ends > > > to the 3' ends for both DNA and RNA.

Protein chains are synthesized from the amino ends > > > to the carboxy ends.

DNA - Coding Strand
(Codons) 5' > > > - - - - - - T T C - - - - - - > > > 3'

DNA - Template Strand
(Anti-codons) 3' < < < - - - - - - A A G - - - - - - < < < 5'

mRNA
Message (Codons) 5' > > > - - - - - - U U C - - - - - - > > > 3'

tRNA
Tranfer (Anti-codons) 3' < < < A A G < < < 5'

Protein - Amino Acid Amino > > > Phenylalanine > > > Carboxy

"the base sequence of codons 57-58 in cytochrome b5 reductase gene is CAGCGC" .... these base sequence of codons are the template strand (anticodons) of DNA. mRNA is synthesized complementary and antiparallel to the template strand of DNA. So the resulting mRNA consists of codons corresponding to those in the coding strand of DNA.

Coding Strand: 5'-CAGCGC-3'
Template Strand: 3'-GTCGCG-5'
mRNA: 5'-CUGCGC-3'

"The mRNA produced will contain the codon sequence ... CAGCGC"
Unless if you assume that the coding strand is the same as mRNA sequence.
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Quote:
Originally Posted by aktorque View Post
...
Coding Strand: 5'-CAGCGC-3'
Template Strand: 3'-GTCGCG-5'
mRNA: 5'-CUGCGC-3'
aktorque's explanation is perfect, up until the very end - since uracil pairs with adenine rather than thymine, it should rather read:

Coding Strand: 5'-CAGCGC-3'
Template Strand: 3'-GTCGCG-5'
mRNA: 5'-CAGCGC-3'

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Old 04-10-2011
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Save It!

Thank you Mondoshawan. Thanks for the correction...
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Old 04-10-2011
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Thanks for the explanation guys...but i still wonder that if we are given some base sequence in exam...how can we find out is this of "coding strand" or "template strand" .....???
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Quote:
Originally Posted by aktorque View Post
Thanks for the correction...
Haha! Usually you're the one correcting me! Happy to return the favor...

Quote:
Originally Posted by manin View Post
Thanks for the explanation guys...but i still wonder that if we are given some base sequence in exam...how can we find out is this of "coding strand" or "template strand" .....???
I guess we'll just have to be careful about the wording they use. The stated "sequence" of a gene is always the coding strand, but they could as easily say, "an mRNA strand is transcribed from a DNA strand with the sequence CGAGTetc", in which case they would be talking about the template strand...
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thanks for explanation.....

i really appreciate it...

but its kinda very trappy question ..

to see whether its coding or template strand is very tough job.....
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Old 07-04-2011
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I still do not quite understand when "codon" is used, is it referring to coding strand or template starnd? Someone told me coding strand is given by default, but is this case, it is the template strand
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