Eukaryotic messenger RNA undergoes several processing steps after transcription

Question

Eukaryotic messenger RNA undergoes several processing steps after transcription before it binds to ribosomes as the template for protein synthesis. One of these steps is polyadenylation. Identify whether the statements below about polyadenylation are true or false 1. A polymerase adds a polyadenylate tail of up to 250 nucleotides to the 5 true end of the mRNA. Incorrect. The polyadenylate tail is added to the 3' end of the transcript. 2. A polymerase adds a polyadenylate tail to the mRNA while it is still in the true false false nucleus. true 3. The polymerase forming the polyadenylate tail uses a polydT DNA template strand. false 4. The polyadenylate tail helps to protect the mRNA from exonucleases. 5. Polyadenylation can occur before or after the mRNA is spliced. false

Explanation / Answer

Answer 1. A polymerase adds a polyadenylate tail of up to 250 nucleotide to 3' end of mRNA and on 5' end capping is done.

2. Its true. A polymerase adds a polydenylate tail to the mRNA while in the nucleus. There are two type of polyadenylation in some cases polyadenylation occurs in nucleas but in few cell short polyadenylation occurs in nucleas and after some time it can be repolyadenylation occurs in cytosol.

3. False as polymerase forming tail do not use polydT DNA template strand instead it uses ATP for synthesis of polyadenylation.

4 it's true polyadenylation tail helps to protect the mRNA from exonuclease activity.

5. False. Polyadenylation only can occur after splicing. Capping and splicing are coupled together. When RNA cap is added and splicing begins before transcription has been completed. Once transcription is complete then only polyadenylation can begin on 3' end

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