In each of the following pairs of molecules, circle the molecule, which is likel

Question

In each of the following pairs of molecules, circle the molecule, which is likely to have the longer half-life and explain why?

mRNA: 5' (N)1,500 (A)40 3' or mRNA: 5'(N)1,500 (A)400 3'

mRNA 5' m^7 G(N)1,500 (A) or mRNA 5' ATG(N)1,500 (A)400 3'

vitellogenin mRNA in tissues treated with estrogen or vitellogenin mRNA in tissues not treated wiht estrogen

protein: +NH2MET(any amino acid)400 COO- or protein: +NH2ARG(any amino acid)400 COO-

protein: (ubiquitin)- +NH2MET(any amino acid)400 COO- or protein: +NH2MET(any amino acid)400 COO-

Explanation / Answer

mRNA: 5'(N)1,500 (A)400 3' has longer half-life compared to other mRNA. It is because other mRNA has shorter poly-A tail. Poly-A tail consist of around 200 Adenine molecules and it prevents mRNA from its degradation. Shorter the poly-A tail shorter is its half-life.

In the second set both mRNA are short lived. It is because, first mRNA has 7-methyl guanosine at 5' end of the mRNA and it does not have poly-A tail where as second mRNA has longer poly-A tail but does not have 5'-cap (7- methyl guanosine). Both these post transcriptional events prevent mRNA from degradation. Not having either of it degrades the mRNA.

vitellogenin mRNA in tissues treated with estrogen Vitellogenin is an egg-yolk precursor protein. Its gene expression is induced by estrogen and estrogen also prevents degradation of vitellogenin mRNA in cytosol. It is found that vitellogenin mRNA is stable for 500 hrs in presence of estrogen while it got degraded in 16 hrs in absence of estrogen.

+NH2MET(any amino acid)400 COO- Methionine amino acid is always coded first while translating the protein. Elongation factors recognizes first amino acid (Met) and then elongation starts. Hence protein should start with Met.

+NH2MET(any amino acid)400 COO- . Ubiquitin is a protein involved in protein degradation. Hence proteins attached to ubiquitin molecules are marked for their degradation through proteosome complex. The process of attaching ubiquitin to protein is known as ubiquitination.

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