Chapter 12, Problem 25A

Summary Introduction

Introduction:

Transcription results in the synthesis of mRNA molecule from DNA molecule. The RNA produced undergoes processing before it is ready for translation. In eukaryotes the original mRNA produced is called pre- mRNA. It contains all of the DNA code.

Answer to Problem 25A

Correct answer :

The correct answer is option C. cap added, introns excised, pony A tail added

Explanation of Solution

Explanation/justification for the correct answer:

Option C. cap added, introns excised, pony A tail added − Before the pre- mRNA leaves the nucleus, introns are removed from it. Further processing adds a protective cap on the 5’ end and a pony A tail to the 3’ end of the mRNA. The cap helps in recognizing the ribosome and the importance of pony A tail is unknown. Now the mRNA is ready to reach the ribosome.

Hence this is the correct option.

Explanation for incorrect answer:

Option A. cap added, introns excised, pony T tail added - Processing of mRNA involves adding of a protective cap on the 5’ end of pre- mRNA and a pony A tail of many adenine nucleotides to the 3’ end of the mRNA. Pony T tail is not added. Hence, this is not the correct option.

Option B. cap added, exons excised, pony T tail added- Before the pre- mRNA leaves the nucleus, introns are removed from it. Further processing adds a protective cap on the 5’ end and a pony A tail to the 3’ end of the mRNA. Exons are not excised. Hence, this is not the correct option.

Option D. cap added, exons excised, pony A tail added - Before the pre- mRNA leaves the nucleus, introns are removed from it. Further processing adds a protective cap on the 5’ end and a pony A tail to the 3’ end of the mRNA. Exons are not excised. Hence, this is not the correct option.