Lecture 22: control of gene expression Flashcards
prokaryotic genes involved in metabolic pathways are arranged in
operons
genes encoding proteins in the same metabolic pathway are
- grouped together on the same chromosome
- transcribed together
- regulated together
prokaryotes arrange genes that multiple proteins are translated from a single mRNA transcript
stop and start codons in the mRNA
operons can be
inducible or repressible
Lactose operon
- inducible
- transcription is normally silenced, but can be activated by presence of lactose
Tryptophan operon
- repressible
- transcription is normally active, but can be repressed by presence of tryptophan
function of the lac repressor
always ‘on’ unless lactose present
allolactose
turns of lac repressor
lactose is a ____ whereas the lac repressor is a ___
disaccharide; protein
chemical modification of DNA or Histone proteins
- reversible
- non-sequence specific
- Heritable: modification can be passed on through mitosis or meiosis
where does Acetyl coA come from during metabolism
oxidation of pyruvate/link reaction
transcriptional control
- availability of the promoter/gene sequences
- specific binding of transcription factors
- coordination of transcription factors
RNA processing
- cell specific alternate splicing of mRNAs
2. 5’ end cap/Poly-A tail: export from nucleus, presence allows translation
translational regulation
- modification of 5’ end cap inhibits translation
- repressor proteins bind t mRNA at 3’ or 5’ UTRs
- sequences of 3’ UTR determine longevity of mRNA
Post-translational modification of polypeptide
- proteolysis-cleavage of the peptide chain
- glycolysation: addition of carbohydrates to proteins
- phosphorylation: addition of phosphate group
- addition of signal sequences directs transport
