Question

Coordinate regulation of gene expression is important both in bacteria and eukaryotes. Operons are used to co-ordinate gene expression in bacteria but NOT eukaryotes. Explain why operons strategy does not work in eukaryotes.

Answer 1

Each cell of the higher organism contains the entire genome. As in prokaryotes gene expression in eukaryotes is regulated to provide appropriate response to biological needs. This occurs in following ways.

1) expression of house keeping genes in most of cells

2) activation of selected genes on demand.

3) permanent inactivation of several genes

Incase of prokaryotic cells most of DNA is organised into genes which can be transcribed. In contrast in mammals very little of total DNA is organised into genes and their associated regulatory sequences. The function of bulk extra DNA is not known.

Eukaryotic gene expression and its regulation are highly complex.

Acetylation of histones leads to gene expression while deacetylation reverses the affects

methylation of DNA results in activation of genes.

The protein-DNA interactions brought out by motifs (helix-turn-helix, zinc finger, leucine zipper, helix- loop-helix) are involved in control gene expression.

Eukaryotic cells have developed several mechanisms to regulate gene expression like gene amplification, gene rearrangement, processing, transport and degradation of DNA.