gene control turning off and on. gene control molecular mechanisms that govern when and how fast...
TRANSCRIPT
Gene Control
Turning off and on
Gene Control
• Molecular mechanisms that govern when and how fast genes will be transcribed and translated. Not all genes are working all the time in all cells
Controls are triggered by…
• Programmed schedules of development (think of a fetus developing in the womb)
• In response to chemical conditions
• Receiving a signal, such as a hormone
Examples of controls
• Programmed schedule: the changes that take place in puberty
• Chemical conditions: Methylation of DNA often inactivates a gene; demethylation might turn it on later
• Acetylation; acetyl group attaches to a histone, loosens the wrap and makes it easier to transcribe
• Receiving a signal: a hormone triggers a response from a cell
What does the controlling?
• Mostly regulatory proteins
• Negative control: slows or stops gene activity (methylation)
• Positive control: turns on or enhances gene activity (acetylation)
Gene Control
• Is different in prokaryotes versus eukaryotes
• Less complicated in prokaryotes
• Often controlled by operons: one promoter and a set of 2 operators. Operator is a binding site for an oppressor.
Prokaryote Example
• Lac operon: controls the production of enzymes that digest lactose. Only turned on when lactose and present and glucose is absent.
• Glucose is the preferred sugar, only make provisions for lactose if it’s the only energy source available
Eukaryote examples
• All cells contain all genes. Many are basic cell function genes that operate regularly.
• Cells also differentiate by activating only certain genes
• For example, a neuron does not do the same thing as a cell in the pancreas
When do the controls happen?
• Page 242-243• Can occur during
transcription, in mRNA processing, in translation, and following translation
Types of Controls in Eukaryotes
• Homeotic genes: interact with others to control development
• X chromosome inactivation makes sure only one X is working in both sexes
• This is dosage compensation (females are mosaics)
More Examples
• Signaling: hormones in animals
• Protein hormones attach to a receptor outside the cell membrane and stimulate a chain of events known as the 2nd messenger system
More Examples
• Steroid hormones pass through the cell membrane to find its receptor inside
• An activator protein winds up next to the promoter for the targeted gene.
• A hormone always triggers a response
Loss of control
• Can mean cancer• Mutations in the
checkpoint genes of the cell cycle and/or repressor genes or enhancer genes lead to too much mitosis