Gene Regulation

Purpose of gene regulation

To conserve ATP and amino acids by only synthesizing proteins which are absolutely necessary, so that these resources are available for use in more essential situations elsewhere, if applicable.

Gene regulation

the process by which gene expression is inhibited or activated

Structural genes

gene responsible for the production of proteins for cellular structure or function

Regulatory genes

genes that code for products that either inhibit or activate expression of structural genes

Promoter region

upstream binding region for RNA polymerase. Identifies start of gene

Operator region

Binding site for repressor proteins, allowing for gene regulation

Introns

non-coding regions within pre-mRNA

Exons

coding regions within pre-mRNA

Termination sequence

signal for DNA to end transcription

Operon

• Linked genes

• regulated by a common promoter and operator region

• transcribed at the same time

purpose of operon

To conserve ATP by ensuring all proteins that are used together are synthesised at the same time, so ATP is not being consumed by producing one in excess

 function of regulatory genes in gene regulation in prokaryotes

• Regulatory genes are separate genes upstream of the operon which code for the repressor protein which binds to the operator region.

• Repressor binds with tryptophan undergoing a conformational shape change allowing it to bind the operator region.

• Obstructs RNA polymerase preventing transcription.

outline tryptophan repression in high trp concentration

• Due to high concentration, tryptophan acts as a cofactor and consistently binds to the inactive repressor protein which normally can’t bind to the operator region.

• Conformational shape change induced in repressor allowing it to bind to operator region.

• Repressor binds to operator region of operon; RNA polymerase is obstructed.

• trp Operon transcription is inhibited.

purpose of attenuation

Attenuation acts as a secondary inhibitor system for repression of the trp operon, increasing the likelihood that no further trp is produced, conserving energy

outline trp operon attenuation in high tryptophan concentration

• Whilst transcription and translation occurs concurrently, the ribosome will not stall at the two trp codons in the leader region during translation as there is sufficient tryptophan resulting in the formation of a terminator hairpin.

• Terminator hairpin causes RNA polymerase to unbind from the DNA and the ribosome to unbind from the mRNA halting transcription and translation before the enzymes for tryptophan synthesis are transcribed.

• The genes coding for the enzymes producing tryptophan are not expressed.