AIIMS 2019 Biology Transcription MCQ Question

Question: m-RNA is formed by

Options: A) Translation
B) Transcription C) Duplication
D) Capping

Correct Answer: (B) Transcription

Explanation:

What is mRNA? mRNA, or messenger RNA, is a type of RNA that conveys genetic information from DNA to the ribosome, where proteins are synthesized. The process through which mRNA is synthesized is called transcription.

Why Transcription is Correct:

1. Definition of Transcription:

   • Transcription is the process of copying a segment of DNA into RNA. During this process, RNA polymerase binds to a specific region on the DNA molecule and synthesizes a complementary strand of RNA. This strand is called messenger RNA (mRNA).
   • The general reaction for transcription can be summarized as: $\text{DNA} \xrightarrow{\text{RNA Polymerase}} \text{mRNA}$

2. Steps of Transcription:

   • Initiation: RNA polymerase binds to the promoter region of the DNA.
   • Elongation: RNA polymerase unwinds the DNA and synthesizes mRNA by adding ribonucleotides complementary to the DNA template strand.
   • Termination: RNA polymerase reaches a terminator sequence, causing it to detach from the DNA and release the newly synthesized mRNA.

Why Other Options are Incorrect:

• Option A and B (Translation):

  • Translation is the process through which mRNA is decoded by ribosomes to synthesize proteins. This is a different process from transcription and does not involve the formation of mRNA. Thus, these options are incorrect.

• Option C (Duplication):

  • Duplication refers to the process of copying an entire DNA molecule or a segment of DNA, which does not involve the synthesis of RNA. This process is unrelated to mRNA formation, making it incorrect.

• Option D (Capping):

  • Capping is a post-transcriptional modification of mRNA, where a 7-methylguanylate cap is added to the 5' end of the mRNA molecule to protect it from degradation and assist in ribosome binding during translation. Capping occurs after mRNA has already been synthesized; therefore, it does not constitute the formation of mRNA.

Summary:

In summary, mRNA is formed by the process of transcription, where DNA is transcribed into RNA by RNA polymerase. The other options listed do not pertain to the formation of mRNA, making them incorrect. Understanding these processes is crucial in molecular biology, particularly in the context of gene expression.