Question

Consider the following double-stranded region of a gene: Strand 17 5'- AATCGTATGCGAAGCCCTTAACT-3' Strand 2 3-TTAGCATACGCTTCGGGAATTGA - 5 The number of mRNA codons in the corresponding transcript is: A 1 3.4 OC5 E Cannot be determined

All are the same diagrams

Answer 1

Question 1 &2

number of mRNA codon in the given template: 5

number of amino acid: 4

Central dogma of molecular biology: this is the production of proteins (amino acids) from the genetic information encoded in the DNA or simply DNA into RNA into PROTEIN. This is brought about by 2steps namely Transcription and Translation.

Transcrption is the process of producing an mRNA from the genetic DNA. This processs happens in the nucleus of the cell. DNA is double stranded with strands running in anti parallel direction. ie. One strand from 5’ to 3’ and opposite in 3’ to 5’. Here the 5’ to 3’ strand is called the sense strand. It is also known as plus strand or non template strand. 3’ to 5’ strand is called the anti sense strand. It is also called as non coding strand -strand or template strand. Nucleotides (monomer unit of DNA) consists of nucleotide base, deoxy ribose sugar and a phosphate group. Nitrogen based of DNA are Adenine(A),Cytosine (C), Guanine (G), Thymine. In RNA this Thymine is replaced by Uracil.

Transciption : The 3’ to 5’ act as the template for the formation of mRNA. Complementary base pairing occurs substituting adenine to Uracil instead of Thymine

for the given example

5’ A A T C G T A T G C G A A G C C C T T A A C T 3’

3’ T T A G C A T A C G C T T C G G G A A T T G A 5’ : Template strand

5’ A A U C G U A U G C G A A G C C C U U A A C U 3’ mRNA

1 2 3 4 5   

start stop

mRNA forms by adding complementary base pair to this given 3’ to 5’ stand. (mRNA strand is exactly the 5’ to 3’ strand replacing T with U. )

now this mRNA moves outside the nucleus to the ribosomes were the proteins are synthesized. There is a start codon to begin the synthesis and stop codon to end the process. Codons are a group of 3 nucleotides with codes for specific amino acids. Each codon codes only for specific amino acid there might be more than one codon for an amino acid

start codon : AUG. protein synthesis doesn’t start until they find a start codon. And AUG always code for methionine.

end codon : UAA, UAG, UGG these are the stop codon and they don’t code for any amino acid. Protein synthesis stops while encountering any one these codes.

Question 3 upstream to 5’ end

Promoter : It the site were the transcription starts by the binding of RNApolymerase enzyme after the unzipping of double stranded DNA helix by the helicase enzyme. In eukaryotes the main promoter sequence are TATAAA , GGGCGG.. AT bonds are easy to break than CG bonds because AT base paring occurs by two hydrogen bonds and CG pairing by 3 hydrogen bonds.