-Timing/coordination of specific events = necessary for normal development of organisms
- cell differentiation results from the expression of genes for tissue- specific proteins
- induction of transcription factors results in sequential gene expression. during development
- Homeotic (HOX) genes are involved in developmental patterns and sequences
- Embryonic induction in development results in the correct timing of events
-. APOPTOSIS (programmed cell death ) plays a role in development/differentiation
- MICRO RNA’s
- regulate genes/play role in development/ control of cellular functions
- Genetic mutations can result in abnormal development
- Environmental factors can influence gene expression EX: temperature and the availability of water determine seed germination in most plants.
• use substances/synthesize macromolecules just fast enough to meet needs
• If substance/enzyme needed, gene is transcribed.
• If substance/enzyme not needed, gene is turned off
• Allows for conservation of cell resources
• Controlling gene expression is one method of regulating metabolism
OPERON – Related genes grouped together with one promoter
• Allows for coordinated control of genes required for metabolism.
• One switch controls more than one gene
• Can be inducible or repressible.
• Not present in eukaryotes
Repressible and inducible enzymes = both examples of NEGATIVE control of a pathway
Activating the repressor proteins shuts off the pathway
POSITIVE control requires that an activator molecule switch on transcription
OPERATORS- regions of DNA that control RNA access to promoter
REPRESSOR - -regulatory protein binds to operator - turns genes off (negative control mechanism) - acts as a braking mechanism - produced at a site away from the operon by regulatory gene.
Repressors alternate between active/inactive forms to control transcription.
• Active form- binds to operator/turns gene off
• Inactive form- conformation change prevents binding to operator
• Binding of REPRESSOR to OPERATOR prevents transcription -RNA polymerase not able to bind to promoter ~ TURNS GENE OFF -
REPRESSIBLE: TRYPTOPHAN trp OPERON
Genes usually TURNED ON;
Repressor = INACTIVE;
Can be turned off by activating repressor
Allows cell to use genes when tryptophan is needed and turn off genes when trp is plentiful
TRYPTOPHAN = corepressor
Presence of tryptophan activates repressor
If TRYPTOPHAN is present, don’t need to make more
* * * * * * * * * * * * * * *
INDUCIBLE LACTOSE lac OPERON
Genes usually TURNED OFF;
Repressor = ACTIVE; binds OPERATOR
Can be turned ON by deactivating repressor
Allows cell to turn on genes needed for lactose digestion when lactose is available
Keeps genes turned off unless needed
ALLOLACTOSE =inducer presence inactivates repressor
Cell only turns gene on when needed