Explain the several reasons on additional levels of complexity are both possible and necessary for controlling expression in eukaryotes?
Gene expression is a complex process that is mediated by several processes. There are around 20,000 genes present in a human genome that codes for certain expressions. The DNA unwinds and initiates the process of transcription through which the template strand is transcribed into mRNA. mRNA is single-stranded and further involved in the process of translation through which the mRNA strand is, with the help of ribosomes synthesizes the polypeptide chain.
Gene regulation involves the expression of certain genes at a time out of all the genes present in the genome. All the different cells of the body require to express genes necessary for them to function. This is determined by some chemical signals that ultimately result in switching on and off of the gene expression.
Eukaryotic gene expression involves several steps:
Chromatin accessibility: - the DNA is present in a condensed form inside the nucleus in the form of chromatin fibers. To initiate the transcription of the genes located on the DNA the uncoiling of DNA is necessary. The more the relaxed form of DNA available in the nucleus, the more transcription of the gene will take place.
Transcription: - This process is mediated by transcription factors that help in the regulation of the mRNA synthesis. Regulatory sequences such as promoters, enhancers, and silencers are responsible for the efficient transcription of the mRNA. These factors may act trans as well as cis.
RNA processing: - the transcribed mRNA is considered as a pre mRNA and is required to undergo further processing. Capping, tailing and slicing is necessary to make an mRNA function. The reason for splicing is the presence of introns which are non-coding sequences present between the exons.
Translation: -this process involves the synthesis of the polypeptide chain according to the sequence of mRNA in the form of codons. The tRNA and ribosomes are responsible for the mediation of this process. Ribosomes act as the site at which the tRNA molecule brings the proper amino acid and also helps in peptide bond synthesis.
Protein activity: -synthesized protein further undergoes modifications such as acetylation, glycosylation, phosphorylation, methylation, lipidation, etc based on their activity.
For a gene to get expressed it has to go through all these stages without any hindrance.
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