Transcript Control of Metabolic Pathways

Control of Metabolic Pathways
Higher Human Biology
Unit 1 – Human Cells
Metabolic Pathways
• Consist of several stages
• One metabolite is coverted to another and so
on
• Each step is controlled by an enzyme
• Each enzyme (protein) is coded for by a gene
(basic)
• If the enzymes are present, the pathway
proceeds
• If one enzyme is absent, the pathway comes
to a halt
Gene(s)
Gene(s)
Gene(s)
• This enzyme action can be regulated at the
level of gene expression (as follows) or
enzyme action (which we’ll come to later)
Control by switching genes on and off
• To prevent wasted resources, some genes that
code for enzymes are switched on and off as
required.
E.g. Lactose Metabolism in E.coli
• Lactose is a sugar found in milk
Glucose
Galactose
Background
• Glucose is used in respiration by E.coli for energy
release
• E.coli can only make use of glucose in lactose if it is
released from galactose
• This is done by ß-galactosidase (enzyme)
• E.coli’s chromosome has a gene that codes for ßgalactosidase
• E.coli only produces ß-galactosidase in the presence of
lactose (gene is switched on)
• It fails to produce ß-galactosidase if lactose is absent
(or if only glucose is present) (gene is switched off)
• LAC operon video
• This is the same video that is on the website
• We call the lactose an inducer as it prevents
the repressor binding to the operator gene. It
leads to the induction of ß-galactosidase.
Jacob Monod Hypothesis
• The hypothesis of gene action was first put
forward by two scientists – Jacob and Monod.
• It has since been supported by experimental
evidence from bacterial investigations.