Question

What is wrong about protein synthesis?

• A. DNA polymerase mediates mRNA synthesis
• B.
  Only one strand of DNA acts as template for mRNA synthesis
• C. mRNA passes into cytoplasm and gets attached to 30S ribosomal subunit
• D.
  tRNA bring amino acids one by one

Answer 1

The correct option is A DNA polymerase mediates mRNA synthesis

Option A
Only the 3’-5’ strand of DNA acts as a template for the synthesis of mRNA. The 5’-3’ strand does not serve as template and is known as the non-template strand. Thus, the statement in Option A is correct.

Option B
1.The synthesis of mRNA by using DNA as a template is called transcription and it is catalysed by the enzyme DNA dependent RNA polymerase or simply RNA polymerase.
2.DNA polymerases are used for the replication of DNA. Thus, the statement in Option B is wrong.

Option C
1.During translation, mRNA passes into the cytoplasm and gets attached to the 30S ribosomal subunit with the help of its ribosomal binding site or Shine-Dalgarno sequence. This is a purine-rich sequence located just upstream of the initiation codon.
2.A pyrimidine-rich sequence on the 3’ end of the 16S rRNA of the 30S ribosomal unit binds with the ribosomal binding site of the mRNA.

Option D
tRNA reads the codon from the mRNA and brings the respective amino acid to the ribosomal site and base pairs with the codon of the mRNA at the site with the help of its anticodon sequence. After the peptide bond formation between the existing polypeptide chain and the newly brought amino acid, the ribosome shifts to the next codon and the next tRNA again brings a new amino acid based on the codon on the empty ribosomal site (A site) and the process continues. Thus, the statement in option D is correct.