Intracellular proteins that bind to specific regions of DNA to control transcription are known as transcription factors. Examples include:
- PIF and DELLA proteins
- Proteins coded by the regulatory genes of the lac operon
- cAMP and the second messenger model
- Products of proto-oncogenes and tumour suppressor genes
Gibberellin and DELLA proteins
DELLA proteins inhibit transcription by binding to a molecule known as PIF. This prevents PIF from transcribing DNA into mRNA. However, DELLA is broken down when the plant hormone gibberellin is present. The PIF is now free to join to the promoter on the DNA and start transcribing it into mRNA, which can then be translated by a ribosome.
In the case of wheat and barley seed germination, amylase is synthesised when the gibberellins destroy the DELLA proteins. This allows the starch in the endosperm of the seed to be broken down to provide a source of carbohydrate for respiration. E.g. the gibberellins turn on the gene for amylase production by destroying the DELLA proteins.
- DELLA: proteins that inhibit the binding of transcription factors. Regulate amylase production in barley and wheat seeds.
- Endosperm: tissue that provides a source of energy for the developing embryo of a seed.
- Gibberellins: plant hormone that is involved in growth, germination and flowering.
- Intracellular: within a cell, as opposed to extracellular meaning between cells.
- lac operon: length of DNA found in E. coli that controls the expression of proteins involved in taking up and digesting lactose.
- PIF: phtochrome-interacting protein, a transcription factor.
- Proto-oncogenes and tumour suppressor genes: genes involved in the regulation of the cell cycle, growth and programmed cell death (apoptosis).
- Second messenger model: a process involving intracellular signalling molecules, such as cyclic AMP, that are triggered by extracellular messengers, such as oestrogen.
- Transcription: the production of mRNA from DNA.
- Transcription factors: proteins that control the flow of information from DNA to RNA by controlling the formation of mRNA.
- Translation: the production of a polypeptide by a ribosome from mRNA.