Question

1. The template DNA strand of the MCB gene is shown below:

5’ ACAGGAGAGTGGAAACATG 3’

What is the sequence of the mRNA produced from this?                                           

A) 3’ TGTCCTCTCACCTTTGUAC 5’

B) 3’ UGUCCUCUCACCUUUGUAC 5’

C) 5’ ACAGGAGAGUGGAAACAUG 3’

D) 5’ UGUCCUCUCACCUUUGUAC 3’

E) 3’ ACAGGAGAGUGGAAACAUG 5’

2. The template DNA strand of the MCB gene is shown below:

5’ ACAGGAGAGTGGAAACATG 3’

What is the amino acid sequence that the MCB gene codes for?

A) MET – PHE – THR – LEU – PRO – CYS

B) CYS – PRO – LEU – THR – PHE – VAL

C) MET – HIS – PRO – LEU – SER

D) MET – CYS – PRO – LEU – THR – PHE

E) MET – PHE – PRO – LEU – SER –CYS

Answer 1

1. (B)

Template DNA strand is the one which dictates mRNA synthesis. Its sequence is complementary to mRNA sequence while the coding or sense strand is the one whose sequence is the same as of mRNA except mRNA has U instead of T.

5’ ACAGGAGAGTGGAAACATG 3’ Temlate DNA

3' UGUCCUCUCACCUUUGUAC 5' mRNA

mRNA is synthesized by an enzyme called RNA polymerase using DNA sequence as the template. mRNA synthesis occurs in 3' to 5' direction using 5' to 3' DNA strand as template.

RNA polymerase is composed of $\alpha$ ₂$\beta$$\beta$^'$\omega$ subunits. It has a crabs claw like shape with the $\beta$ $\beta$^' forming pincers holding the template. mRNA synthesis is coupled to translation (process of protein synthesis) in bacteria.

proteins are synthesized by the ribosomes using mRNA as a template. Each amino acid id encoded by a triplet nucleotide sequence called a codon. Each codon codes for only 1 amino acid while an amino acid can be encoded by several codons (degeneracy). AUG serves as a start codon and also codes for Met.

2. None of the options shows correct amino acid sequence.

5' ACAGGAGAGTGGAAACATG 3' template DNA

3' UGUCCUCUCACCUUUGUAC 5'

5' CAU GUU UCC ACU CUC CUG U 3' mRNA sequence

N terminal His-Val-Pro-Thr-Leu-Leu c terminal