Question

Describe the types of interactions that regulate gene expression. (Please use these terms in your answer)

Regulatory sequences

Epigenetic changes

Histones

Phenotype

Tissue specific proteins

Transcription factors

Answer 1

The term gene expression indicates the ability of a gene to express itself, that is to undergo transcription and translation. It is regulated both spatially and temporally.

All the genes are not switched on in all the cells. For example, a gene encoding for hemoglobin is switched on in red blood cells but not in white blood cell. This is spatial regulation. This is also called as tissue specific gene expression which results in the formation of tissue specific proteins.

A gene encoding for a protein against viral infection is regulated only when there is a viral attack. This is an example of temporal regulation.

The ultimate aim of gene expression is to produce proteins which are the final players of gene expression. These proteins are responsible for the changes in the phenotype of the cell which is actually we call as gene expression.

Gene expression is regulated by two ways, by the nucleotides sequence of DNA and by the histone protein associated with DNA.

The nucleotide sequences of DNA are called as regulatory sequences. They are of two types mainly, enhancers and silencers.

Enhancers are the sequences which are bound by proteins called as activators and result in an increase in the rate of gene expression.

Silencers are the sequences which are bound by proteins called as repressors/insulators and result in a decrease in the rate of gene expression.

Promoter is the region on DNA which is bound by RNA polymerase to initiate the transcription of the genes. The sequence of promoter is highly conserved across organisms. More the sequence of the promoter is conserved, easier will be the accessibility of RNA polymerase towards the promoter and therefore a higher rate of transcription will be observed. Apart from RNA polymerase, specific protein called as General transcription factors and specific transcription factors bind to the promoter region to help in the recruitment of RNA polymerase and increase the efficiency of transcription.

The gene expression regulated by histone proteins is called as epigenetic inheritance or epigenetic regulation. It is carried out by the chemical modification of specific amino acid residues of the histone proteins. These modifications results in either tightening of chromatin and thereby decreasing gene expression or loosening of chromatin and thereby increasing gene expression. In general, acetylation increases expression and methylation decreases gene expression. Phosphorylation can increase or decrease gene expression. Other types of chemical modification include ribosylation, glucosylation, sumoylation ubiquitination etc.

This is how the expression is regulated in two ways.

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