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Gene Expression I

Lactose Operon It is an inducer, inducer presented to the cell is 1, 6 Allolactose. It has a regulator gene and structural gene
Name the make up of the structural gene and the different parts Characterized by an operon made up of a polycistronic mRNA. It has a p and o region as well as z, y and a region
What does the z, y and a region correspond to z= B-galactosidase, y=permease, a=transacetylase
What it is function of the i gene? i gene elaborates mRNA referred to as imRNA which is responsible for the synthesis of a transcription factor that acts as a repressor
What does the repressor bind to? It binds to the o (operator) region and prevents transcription of z, y and a
What is a pallindromic sequence? It is an inverted repeat, top and bottom strand are the same when read 5' to 3'
How does the repressor recognize the sequence? Due to its helix-turn-helix motif. Repressor straddles DNA in G-C residues of palindromic sequence of the operating site
How do you turn on the lac operon? You need a lack of deficiency in glucose (product of B-galactolose)
What happens to cAMP when glucose goes down? cAMP goes up via activation of adenylyl cyclase, cAMP binds to CAP, cAMP-CAP complex facilitates the maximal binding of RNA polymerase when at the P site & o site is empty.
What does the binding of IPTG induce the repressor to do? Binding of IPTG induces conformation changes in the repressor such that they no longer interact productively with DNA
Tryptophan operon similarities to lac operon Encodes for repressor, polycistronic mRNA encoding for 5 cistrons A-E which give rise to 3 enzymes for trp biosynthesis, p & o sites
Trp operon differences to lac operon very poor repressor (inactivated at first), followed by a sequence of nucleotides (162). In the 162 nts, there is a attenuator sequence which enables couple transcription-translation in Prokaryotes. Tryptophan rich region present.
What does the sequence 3/4 pairing signify? Rho independent termination
How do you change a Heterochromatin to Euchromatin? Change the status of methylation at the GC island or acetylation of the histone
What happens if m5C undergoes spontaneous deamination? It gives rise to thymine which when under another round will give a AT base pair (transition mutation)
Methyltransferases DNMTs (DNA methyltransferases)-uses S-Adenosyl methione as methyl donor
How does MSPI and HpaII check methylation status? They are isoschizomers that recognize CCGG. MSPI can cut methylated internal C. HpaII cannot cut methylated internal C.
How is DNase I used to check methylation state? In an undermethylated state, less DNase required/sensitivity to DNase I is increased
Euchromatin Hypomethylated state, gene expression is robust
Heterochromatin Hypermethylated state, DNA is repressed
Epigentetic control mechanism Changes do not reflect changes at the level of DNA sequence
DNA methylating agents One is a base, other is a deoxynucleoside. Induce a state of demethylation, put a N on position 5 instead of a C. Ex. Decitabine
MeCP role Can bind to methylated CG islands referred to as CG binding protein. (recruitment of HDACs often associated). They organize chromatin into a status that is resistant to DNase I degradation.
E globin & Y globin methylation status at week 6 and 12 6 weeks= E-unmethylated promoter/maximally expressed, Y-methylated promoter/minimally expressed. 12 weeks=E becomes methylated and Y becomes unmethylated
Histone modification occurs at which histones H3 and H4 more often, at the N terminus
Lysine 9 of H3 Is subjected to acetylation and methylation
Bromo Domain Can recognize acetylation of histones, has specific affinity for Acetyllysine
Chromo Domain Can recognize methylation of histones
HAT Histone acetyl transferase-consumes CoA
HDACs Histone deacetylase. Trichostatin is a HDAC inhibitor
Describe process of methylation with lysine 9 of H3 Recruits HP1(heterochromatin protein 1). HP1 binds to DNMT and then methylation status changes. DNA methylation does not occur randomly
What can DNA bind once it is methylated? It can bind MeCP2 which can recruit HDAC & induce de-acetylation of the histone



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