Question

1.) Explain how combinatorial control makes it possible to have far fewer transcription factors than the number of genes that are transcriptionally regulated.

2.) If a miRNA were 5 nucleotides long, what is the chance of finding a complementary sequence in a randomly selected 5 nucleotide sequence in mRNA? [Assume mRNA sequences to be random and that mRNAs have an equal amount of each nucleotide (A, U, G, and C)]. If an miRNA were 10 nucleotides long, what is the chance of finding a complementary sequence in a randomly selected 10 nucleotide sequence in mRNA? If you were designing a synthetic miRNA to specifically target a particular mRNA, would you want to design a 5 or 10 nucleotide long miRNA? Why?

3.) In the fungus Neurospora crassa, roughly 2 – 3% of cytosines are methylated. Researchers isolated Neurospora DNA sequences that contained 5-methyl cytosine and found that almost all methylated sequences were located in inactive copies of transposable elements. On the basis of these observations, propose a possible explanation for why Neurospora methylates its DNA and why DNA methylation in this species is associated with transposable elements.

4.) Some cases of bacterial gene regulation involve use of alternative transcriptional terminators. Propose a plausible way that a riboswitch could function in the use of alternative bacterial transcriptional terminators.

Answer 1

In a particular organism the net amount of gene outnumber the amount of trabscriptional factors.For eg.in human the total number of gene is geter thamn the sum of transcriptional factors,i.e 25000 gene and transcriptional factors 1850.The combination of multiple protein also called combinatorials take part in the gene expression and regulation by limted number of transcriptional factors.Cis regulatory modules is the major reason of the combinatorial control of gene expression.These cis reulatory sites are present in the DNA sequences specific for specific transcription factors located in the enhancer and promoter region.These cis regulstory factors control the transscription of particular gene according to the combination of transcriptional factors which will start or stop the translation process.

3)The DNA methylation is a serious matter and it happends in our nucleic acid due to mutaion which some time results in phenotypic variata the methylation is needless ion and diseases.But in fungi like Neuropspora the methylation is needless or non essential.The cytosine methylation mechanism of Neurospora is done at transposone regions where repeatitive sequence are found and it is done for the genomic defence.Higjly methylated non coding sequences in transposones are caLled disi independent RNA or disi RNA loci DNA methylation.They are found highly methylatedor the methylation are seen highly in 5 mC.

4)In bacterial gene regulation mechanism transcriptional termination is common and found in 5'UTR gene operon.cis acting RNA bases regulation take part in transcription termination,riboswich is one of the cis acting RNA regulator which assist in changing the structure of the transcription site and stops the transcription prematurely.Roboswich changes the RNA folding to decides if the transcription has to be terminated or anti terminated.The hair pin loop formation blocks the pathway thus leads to termination.The roboswich mechnism help in finding crystal structure and in pahrmaceuticals.