1) Translation of a typical prokaryotic gene is initiated at a single start codon (AUG). However,...

1) Translation of a typical prokaryotic gene is initiated at a single start codon (AUG). However, the 5’ untranslated region of a prokaryotic mRNA can contain multiple AUG triplets. Explain how the translation machinery recognizes the correct AUG codon and initiates translation specifically at the start codon of a polypeptide.

Which event is involved in the initiation of transcription?

a. The binding of helicase to the origin region of template DNA

b. The binding of initiation factors to the start codon

c. The binding of RNA polymerase to the promoter region of template DNA

d. The binding of DNA polymerase to the promoter region of template RNA

e. The binding of the repressor to the operator region on DNA

In contrast to prokaryotic mRNA, eukaryotic mRNAs have a poly(A) tail of 20 to 200 adenine nucleotides in a row. Does the DNA coding strand of eukaryotic genes contain long strings of adenine nucleotides?

yes or no?

Expert Solution

Ans 1. Prokaryotic mRNA contain various AUG codons which act as start codon. But which AUG actually act as the start codon is determined by a conserved polypurine sequence, AGGAGG, located about 7 nucleotides upstream of the AUG initiation codon. This is known as Shine Dalgarno sequence. Only tRNAfmet binds to ribosome in response to AUG codon in mRNA. Then initiation factors bind, two subunits of ribosome bind and translation begins.

Ans 2. C. Binding of RNA polymerase to promotor region of template DNA.

RNA polymerase is a holoenzyme having a sigma factor ( regulatory function in the initiation of RNA transcription). This sigma factor along with RNA polymerase bind at the promoter sequence and transcription begins.

Ans 3. Poly A tail is added after transcription is over or say when newly formed transcript is getting cleaved from the transcription bubble. This long stretch of Adenosine residues help mRNA in leaving the nucleus and entering the cytoplasm for translation. Poly A tails prevent mRNA degradation and enhance its stability. So it is added later after transcription, is not present in DNA coding strand.

gladiator answered 2 years ago

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