Question

Give two examples of inducible/repressible gene expression. Explain the function of the genes, the mechanism of the regulation, and why it is important to have a way to control the level of gene expression.

Answer 1

Genes are the coding region of a DNA and they code for proteins. Proteins are integral part of all kinds of metabolism in the body and is required in varied functions of a normal body. The gene is made of dNTPS (deoxyribonucleotide triphosphate, the GTP, ATP,CTP and TTP). the order in which they occur is termed as a codon this sequence codes for amino acid sequence in the corresponding order. The amino acids in a particular sequence is known as peptides and they in large chains with secondary, tertiary and quaternary structures form the proteins. These proteins as mentioned in turn regulate a variety of functions in the body, they are one of the major building blocks of the body.

The genes coding for amino acids and making corresponding proteins is called gene expression, which consists of two major steps, the transcription and translation. Transcription takes place in the nucleus of a cell and there the DNA sequence is used as a template for the transcription of a corresponding mRNA molecule, this mRNA then enters the cytoplasm and reaches a ribosome where the mRNA is translated into a protein. This entire process of transcription and translation is referred to as gene expression.

Gene expression is regulated at various levels like at transcription, post transcriptional RNA processing, RNA transport regulation, during translation and post translation. This results in an increase or decrease of the functional gene product, the protein. This is decided based on external stimuli or based on the internal requirements. The regulation of gene is brought about by a cassette of elements which comp[rise the operon. The gene operon is under regulatory regions like promoters (are close to the gene) and enhancer binding sites (can be anywhere and not compulsorily close to the gene), whereas the operators, gene and terminators comprise the operon.

The promoters are further regulated by inducers or repressors. Thus inducible or repressible gene expressions. Inducers are molecules or metabolites which turn on the expression of a gene as when required. Repressible gene expression involves the turning off of the otherwise continuously expressed gene via repressor molecules. Examples are Lac operon mediated gene expression - Inducible, and the  Trp operon mediated gene expression - repressible gene expression.

It is important to regulate the gene expression of all genes at all times except some house keeping genes which needs to be expressed all the time. Since the genes are part of normal development and maintenance of the body it has to regulated according to the requirements of the cell in response to external changes or as required by the body for energy and development or even for eliminating waste. Thus the required genes are turned on or induced and the other genes at that scenario which is not required is turned off or repressed. And this comprises gene regulation. Imagine a scenario where a gene encoding a metabolite in glucose metabolism is continuously turned with out regulation, the out come will be uncontrolled cell proliferation due to excess of energy resources made available by this erroneous glycolysis. This is a typical scenario of cancer cells, where the cells proliferate without any control. Or consider when a required gene is repressed all then time, in the absence of that particular molecular event a deficiency of the functional product of the gene happens leading to deficiencies or disorders. Hence a gene needs to be regulated all the time according to its function and requirement of the cell or body on the whole.