Unit 3 - Gene Expression Flashcards
(49 cards)
Gene regulation
involves turning genes on or off depending on their products r required
Regulators (2) types
r the proteins that switch genes on or of:
1) activators (gene on)
2) repressors (gene off)
Housekeeping genes
ALWAYS NEEDED
- constantly being transcribed/ translated (ssbp)
- most genes r not HK genes
Transcription
in the nucleus = product mRNA
Translation
in the cytoplasm = product protein
4 levels of control in gene expression
1) transcriptional
(mRNA being synthesized)
2) posttranscripional
(mRNA being made)
3) translational
( protein being synthesized)
4) posttranslational
(after protein has been synthesized
Transcriptional regulation
- regulation of which genes r transcribed
- can involve cortrol of the rate t occurs
a) controlling chromatin structure
b) enhancer regions on DNA
Chromatin Accessinilty
the structure of chromatin (DNA and its organizing proteins) can be regulated. More open or relaxed chromatin makes a gene more available for transcription (+ of acetyl group to histones loosens their association w DNA and promoter bc accessible)
Methylation transcriptional regulation
a methyl group is + to the cytosine bases in the promoter of a gene inhibiting transcription This silences the genes for a period of time
bone marrow
produce red blood cells, use specific enzyme to remove methyl group and allow transcription
Alternative splicing
perhaps 75% of human gens r alternatively splices at the pre-mRNA level
binding masking proteins to mRNA
when the mRNA is associated w a masking protein it does not undergo protein synthesis
regulation changes the rate of degradation of mRNAs
-regulatory mols such as a hormone, will directly or indirectly affect the rate of mRNA breakdown
ie. mammary gland of a rate it takes 5h for half of the mRNA for milk protein to break down and in the presence of the hormone prolactin time increases to 92h
mRNA transcription r translated into proteins
ie. length of Poly A tail increases or decreases how long translation take place but scientists r not really sure how this works
Posttranslational Regulation
controls when proteins bc fully functional, how long they r functional and there degradation (modifications made to the polypeptide chain)
ie. proteins go from inactive to active from processing mechansims (special chemical group can be added or removed from protein )
Prokarytotic; gene regulation
gene expression in P is regulated in response to the concentration of two mols:
- lactose
- tryptophan
Lac operon vs Trp operon
both - feedback
lac = uses a single mol (lactose ) that induces the expression of operon genes
trp = a single mol of (tryptophan) that represses the expression of the operon genes
Operon in prokaryotes
a cluster of genses under the contril of one set of regulatroy sequence
regulatory sequence (2)
1) promoter = the site where DNA transcription begins
2) operator = the sequence of bases that control transcription
Strucural genes
coding regions which code for the specific proteins
Operator sequence
regulator protein binds
- depending on the regulator, binding to the operator causes either activation transciption or repression transcription
effector of operator (3)
1) acts on the regulator protein
2) can be an inducer (stimulates)
3) can be a corepressor (inhibits)
Lac Operon (-) regulation
the sugar lactose, a potential source of energy from prokaryotes must be acquired directly from the environment. required for lactose metabolism, prokaryotes use lac operon
Lac Operon (3)
1) lactose = glucose + galactose
2) dissacharide in milk
3) e.coli: b-galactoside catalyses the cleavage of the bond in lactose
