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Repressible systems - A repressible system is on except in the presence of some molecule (called a corepressor) that suppresses gene expression. The molecule is said to "repress expression". The manner by which this happens is dependent on the control mechanisms as well as differences between prokaryotic and eukaryotic cells.
In prokaryotes, the term corepressor is used to denote the activating ligand of a repressor protein. For example, the E. coli tryptophan repressor (TrpR) is only able to bind to DNA and repress transcription of the trp operon when its corepressor tryptophan is bound to it.
The L-arabinose operon houses genes coding for arabinose-digesting enzymes. These function to break down arabinose as an alternative source for energy when glucose is low or absent. [ 4 ] The operon consists of a regulatory repressor gene (araC), three control sites (ara02, ara01, araI1, and araI2), two promoters (Parac/ParaBAD) and three ...
Enzymes are evolved to catalyze a particular reaction on a particular substrate with high catalytic efficiency (k cat /K M, cf.Michaelis–Menten kinetics).However, in addition to this main activity, they possess other activities that are generally several orders of magnitude lower, and that are not a result of evolutionary selection and therefore do not partake in the physiology of the organism.
Function: Amylase is an enzyme that is responsible for the breaking of the bonds in starches, polysaccharides, and complex carbohydrates to be turned into simple sugars that will be easier to absorb. Clinical Significance: Amylase also has medical history in the use of Pancreatic Enzyme Replacement Therapy (PERT). One of the components is ...
An adaptive enzyme or inducible enzyme is an enzyme that is expressed only under conditions in which it is clearly of adaptive value, as opposed to a constitutive enzyme which is produced all the time. [1] [2] The inducible enzyme is used for the breaking-down of things in the cell.
Cytochrome P450 enzymes also function to metabolize potentially toxic compounds, including drugs and products of endogenous metabolism such as bilirubin, principally in the liver. The Human Genome Project has identified 57 human genes coding for the various cytochrome P450 enzymes.
Several cell function-specific transcription factors (among the about 1,600 transcription factors in a human cell) [68] generally bind to specific motifs on an enhancer. [69] A small combination of these enhancer-bound transcription factors, when brought close to a promoter by a DNA loop, govern transcription level of the target gene.