Question

37. Genetic regulation in eukaryotes can take place at a variety of levels from pre- transcriptional to posttranslational. At what level is genetic regulation considered most likely in prokaryotes? A) polyadenylation of the 3' end of the mRNAs B) capping ranscriptional D) intron processing E) exon skipping

please in as MUCH detail explain why this is the answer. what are pre and post trans/transl. and ALSO please explain what A through D are (definition and what it refers to in genetics)

Answer 1

C) Transcriptional.

Well, gene regulation is almost 1/4 th of complete Molecular biology course. I will try to give as much detail as possible. Take it as an introduction to start with.

Gene are expressed from the DNA by the help of enzyme RNA polymerase (RNA Pol II for eukaryotes). So, now there is a question, if all the cell types in an eukaryotes contain a complete genome, so every kind of gene will express in every cells and all the cells will have same proteins present. So, think about it, what will be the after effect, our body might take a thalaus like structure where every cells are same. But this kind of situation does not happen. Because though all the genes are present in every cells only a subsets of genes are expressed in different cell types.

Now, pre-transcriptional regulation is generally dictated by the environment, or specifically saying signaling molecules from the other endocrine or paracrine cells. Specific signaling molecules will bind to the cellular receptor resulting a downstream signaling pathway which will later express specific set of genes.

Transcriptional regulation is when a set of trans acting proteins will become active and will bind to the regulation site (cis acting site of the DNA) to express or repress certain genes. This regulation is present for both the prokaryotes and eukaryotes.

For eukaryotic genome we know that introns are present in the DNA. So, at the time of transcription, all the exons and introns are transcribed to the mRNA. Now, to get rid of the introns and to make a continuous chain of exons, splicing event happen.

Sometimes, alternative splicing happen, where from a single pre-mRNA two or more different kind of mature mRNA are formed to give rise to different proteins by skipping or rearranging one or more exons

Now, for prokaryotes translation happen along with transcription inside the cytoplasm but for eukaryotes the mRNA has to come out from the nucleus to the cytoplasm. To increase the stability of the mRNA, in eukaryotes mRNA are further processed in both the 5' and 3' end. At the 5' end it get a cap of guanine nucleotides and at the 3' end a poly A tail is formed by polymerizing the adenosine bases by the help of enzyme polyadenylate polymerase (this poly A tail is a untranslated region).

Now after all the processing of mRNA, a mature mRNA is translated. For eukaryotes a lots of post translational modification happens (like N linked and O linked glycosylation, modification of certain amino acids, cleavage of certain amino acid sequence) inside the ER and golgi bodies.