Regulation of Gene Expression

Both Prokaryotes and Eukaryotes cells need to regulate which genes are expressed at a certain time. This includes environmental and internal cues. In other words this regers to whether or not transcription will occur allowing for cell specialization.

Operon

-The group of genes that can be turned on or off. Three parts include the promoter, operator, and genes. 

Promoter= where RNA can attach

Operator= the on/off switch

Genes= code for related enzymes in the pathway 

-Can be repressible or inducible

Repressible meaning transcription is usually on, but can be repressed

Inducible meaning transcription is usually off,  but can be induced

Regulatory Gene

-Produces a repressor protein that will bind  to the operator to block RNA polymerase from transcribing the gene. The gene is always expressed but at low levels and the biding of the repressor to an operator is reversible.

Repressible Operons like TRP Operon

The trp operon in bacteria controls the synthesis of tryptophan, this process is repressible meaning that transcription is active. however, it can switched off by the trp repressor. Additionally, Allosteric enzymes are only active when tryptophan binds to it and if there is too much tryptophan, bacteria build-up. Therefore causing tryptophane  to more likely to bind the repressor turning it active, which will then temporarily shut off the transcription for tryptophan. 

Inducible Operons like the lac operon

The purpose of the lac operon is to regulate the synthesis of lactase, which is an enzyme that digests lactose. Furthermore due to its inducible nature, transcription is off meaning that a lac repressor is bound to the operator. The inducer for the lac repressor is allocator and when it is present it will bind to the lac repressor and turn the lac repressor off. As a result, genes can be transcribed. 

Eukaryotic Gene Expression

The phenotypic expressionthe of a cell or organism is determined by the random combination of genes that are expressed and the level/regulation in which they are expressed. The differences between cell types are called differential gene expression. However Eukaryotic gene expression in particular is regulated at different stages.

These stages include Chromatin structure where DNA is tightly wounded causing it to be less accessible for transcription. But, it can be modified by Histone acetylation adds acetyl groups to histones which looseness the DNA, and DNA methylation adds methyl groups to DNA, which causes the chromatin to condense. 

Epigenetic Inheritance refers to chromatin modifications not altering the nucleotide sequence of DNA but can be inherited in future generations.  However, these modifications can be reversed, unlike mutations.

 Transcription Initiation is when the chromatin modifications allow DNA to be more accessible allowing special transcription factors to bind to control elements. Gene expression is increased or decreased because of the binding of activations or repressors to control elements.  Translation inhibition refers to how it can be activated or repressed by initiation factors with microRNAs and small interfering RNAs biding to mRNA and degrading it or blocking translation.

RNA procession includes alternation splicing of pre-mRNA.