Question

a. What percent of the genome is thought to be functional, if including RNA? What role does the transcriptome (and specifically microRNAs) play in the cell?

b. Describe the process of microRNA function. What is the difference with regards to the source of miRNA and siRNA?

Answer 1

a. Not more than 25 percent of the genome is functional at least in case of humans and rest of them is known as true junk DNA as they are harmless and useless and also because their function is still not known.

Transcriptome can be regarded as the total RNA molecules in a cell or a population of cells. It can be also regarded as the subset of proteome which is the total protein content of the cell. Unlike genome content transcriptome can vary in a given cell depending on varying conditions such as stress, any developmental change etc. the transcript level reflects the genes that are actively expressed or repressed except for the RNA degradation.

microRNAs are small 22 nucleotides RNA which do not code for any protein and basically are involved in regulatory processes at the post transcriptional level by inhibiting or repressing the function of the RNA.

b. MicroRNAs are small non coding RNA which play regulatory role at the posttranscriptional level. They are evolutionarily conserved and they are transcribed by RNA pol II or pol III forming precursors which is then cleaved sequentially to form the final mature micro RNA. The function of microRNA is achieved through two ways: one is RNA degradation and the other is translation inhibition. In both the cases the silencing is mediated through a complex formation called as RISC (RNA induced silencing complex). When Extensive base base pairing occurs between target RNA and microRNA occurs it leads to fragmentation of the RNA finally degrading it whereas minimal base pairing of the target RNA and the microRNA results in translational repression.

Both miRNA and siRNA can lead to gene silencing. miRNA is typically produced endogenously inside the cells and are single stranded whereas siRNA are double stranded and are taken up by the cells exogenously through viruses or external vectors, plasmids.