Question

In Bacteria, translation of nascent RNA transcripts is often initiated before transcription is terminated. When this occurs: Select one: a. RNA is transcribed 3'=>5' and amino acids are added to the carboxy terminus of the growing polypeptide as the ribosome moves 5' => 3' along the mRNA b. RNA is transcribed 5'->3' and amino acids are added to the amino terminus of the growing polypeptide as the ribosome moves 3'=> 5' along the mRNA c. RNA is transcribed 3'=> 5' and amino acids are added to the amino terminus of the growing polypeptide as the ribosome moves 3' => 5' along the mRNA d. RNA is transcribed 5'->3' and amino acids are added to the carboxy terminus of the growing polypeptide as the ribosome moves 5' =>3' along the mRNA

Answer 1

1. RNA polymerase transcribes RNA from the 5' to 3' , that is nucleotides complementary to the template DNA strand are added to the 3' end. Translation, that starts simultaneously with transcription in bacteria also occurs in the same direction, i.e ribosome binds to a sequence near the 5' end of the mRNA to initiate translation and the amino acids are added to the carboxy terminus of the growing polypeptide.Therefore option d. is correct .

2. In bacterial translation, the 16srRNA in the small subunit (30S) of the ribosome has a sequence complemmentary to the shine dalgerno sequence or ribosome binding site (rbs) present in the mRNA ,just before the start codon.Once the small sub unit binds to the mRNA the large subunit is recruited and initiation of translation occurs. Therefore, option b. is correct.

Option a. and d. are wrong as the small subunit binds first and not the large subunit. Option c. is wrong because the protein doesn't bind but the ribosomal RNA in the 30S subunit binds, option e. is wrong as the rbs is a sequence that occurs before the code for methionine hence it doesn't base pair with methionyl tRNA.