#6: Controlling Gene Expression Flashcards
Controlling Gene Expression (Importance)
Organisms must be able to respond the their environment
If not regulated - waste of time, resources, and energy
- Transcriptional
regulates the transcription of a gene
Examples of Transcriptional
- access of promoters provided by loosening of DNA molecule from histones
- activator and repressor protein binds to promoter and enhance/decrease rate of transcription
- methyl groups added to “C” bases, so RNA polymerase cannot bind and transcribe - silence genes
- Post-transcriptional
regulates the modification of mRNA strand
Examples of Post-transcriptional
- alternative splicing occurs -different combos of interns removed and exons spliced together
- masking protein bind to mRNA and inhibit further processing
- rate of degradation of mRNA depends on cell need
- Translational
regulates the translation of mRNA
Examples of Translational
- variation of lengths of poly-A tail related to rate of translation
- Post-translational
regulates the ability of a pr- to function
Examples of Post-translational
- processing occurs -polypeptide chemical modification to render active protein
- present of hormones may lengthen/shorten length of time protein is functional
- Ubiquitin-tagged protein degraded
Operons
used by prokaryotes to regulate gene expression at the transcriptional level
Promoter (component of operon)
binding site for RNA polymerase
Operator (component of operon)
will regulate whether or not RNA polymerase can pass through and transcribe the gene
Gene(s) (component of operon)
sequence of DNA that is transcribed to produce specific pr-
Inducible gene regulation
the genes are normally NOT expressed
the expression of the genes are INDUCED by the presence of another molecule
Repressible gene regulation
the genes ARE usually expressed
the expression of the genes are REPRESSED by the presence of another molecule
lac Operon
used by prokaryotes to control the production of b-galactosidase
b-galactosidase
enzyme responsible for breaking down lactose
Lactose
disaccharide consisting of glucose and galactose
found in milk products
the energy released from the breakdown of lactose can be used for growth in prokaryotes
When lactose is absent…
lacI pr- binds to the operator and inhibits the transcription of the genes
When lactose is present…
binds to the lacI pr- and changes its shape
after changing shape, the lacI pr- is no longer capable of binding to the operator and transcription occurs
lac operon is an example of…
inducible gene expression
genes are normally not expressed and the presence of lactose induces their expression
trp Operon
used by prokaryotes to control the production of tryptophan (an amino acid)
tryptophan
prokaryotes contain enzymes that are used to produce tryptophan from precursor molecules
the trp operon controls the expression of these enzymes
When tryptophan is absent…
trp repressor pr- (trpR) is unable to bind to the operator
as a result, the genes needed for the production of tryptophan are transcribed
