Gene Regulation

DNA is in every cell

mRNA only copies DNA genes that are useful to the cells

cell function is dependent on the proteins produced

• ​pancreas - insulin

• ​blood cell - haemoglobin

• ​stomach - HCl

• ​salivary gland - saliva

​Gene - a section of DNA that code for polypeptides and functional RNA and are located at a fixed locus on a DNA molecule.

​DNA - is used to give instructions for the production of proteins in the process of protein synthesis.

​Gene Regulation - is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein).

​Gene regulation can occur at any point during gene expression, but most commonly occurs at the level of transcription (when the information in a gene's DNA is passed to mRNA).

Rate of mRNA Synthesis (Transcription) - There are proteins that can bind to certain gene regions to increase the rate of transcription, like the transcription enzyme RNA Polymerase.

mRNA degradation - There are proteins that can bind to certain gene regions to decrease transcription to the point that it may not transcribed at all.

​Expressed all the time

• ​genes responsible for routine, continuous metabolic functions (for example, respiration), common to all cells, continuous throughout life

​Expressed at a selected stage in cell or tissue development

• ​as cells derived from stem cells are developing into muscle fibres or neurones, for example

​Expressed only in the mature cell

• ​genes responsible for antibody production in a mature plasma cell, after these have been cloned

​Expressed on receipt of an internal or external signal

• ​when a particular hormone signal, metabolic signal, or nerve impulse is received by the cell, such as the gene for insulin production in β cells in the islets of Langerhans

​Regulation of gene action is partly regulated by the genes themselves

​Many genes code for specific enzymes or proteins required by working cells at some stage.

​Other genes regulate other gene.

​Structural genes

• ​code for a structural protein, or an enzyme, or an RNA molecule not involved in regulation

• ​required by cells to create or maintain the structure, or enable the functioning, of the cell or organism

• ​transcribed into proteins

​Regulatory genes

• ​involved in controlling the expression of one or more genes

• ​may code for a protein or for an RNA molecule

​Genes are also regulated by ‘signals’ from the environment – typically from within the cell.

These act on the enzymes or on the genes that code for them.

​Inducible enzymes

• ​produced under specific conditions, such as the presence of a particular substrate

• ​controls the expression of one or more genes, structural genes, involved in the metabolism of that substance

• ​in the absence of the substrate, gene action is switched off

​Repressible enzymes

• ​generally produced continuously, but their production can be halted

• ​formed unless a signal, such as an excess of product, turns their production off

​Lac Operon in Prokaryotes

• ​a mechanism that ensures that the enzymes required for the metabolism of lactose are produced only in the presence of lactose. It has been observed in bacteria, such as E. coli

​Regulation in Eukaryotes by enhancers and transcription factors

• In eukaryotes, before mRNA can be transcribed by the enzyme RNA polymerase it first binds together with a small group of proteins called general transcription factors at a sequence of bases known as the promoter.