(Exam 2) - Chapter 7: Transcriptional Regulation

3 enzymes transcribed together for lactose metabolism

ß-galactosidase, lactose permease, transacetylase

operon

single unit of genes encoding for enzymes

o (operator)

a gene adjacent to the transcription initiation (involved in transcription control)

i

a gene that encodes a protein that binds to the operator

repressor

normal i gene product

repressor function

blocks transcription when bound to o

the lac operon is an example of this type of regulatory control

negative (binding of the repressor blocks transcription)

cis-acting control elements

affect expression of linked genes on the same DNA molecule

example of a cis-acting control element

the i-gene

negative control

the regulatory protein blocks transcription

positive control

the regulatory protein activates transcription

result of glucose presence in E. coli

lac operon is repressed, even in presence of lactose

enhancer

a regulatory sequence located farther away from the start site (upstream or downstream)

enhancer function

help regulate RNA polymerase by binding transcription factors

cohesin

ring-shaped protein complex that allows contact between the target gene and the transcription factor

function of transcriptional activators

bind to regulatory DNA sequences and stimulate transcription

2 domains of transcriptional activators

DNA binding domain, activation domain

1st mechanism of the activation domain

interact with mediator proteins and general transcription factors

2nd mechanism of the activation domain

modification of chromatin structure

type of chromatin that typically binds transcriptional activators

euchromatin

elongation is regulated by:

direct modulation of RNA polymerase activity, and effects on the chromatin structure

NELF and DSIF

negative regulatory factors that bind to RNA polymerase II and stop elongation

P-TEFb function

resumes transcription by phosphorylation of NELF and DSIF

epigenetics

modification that does NOT happen on the DNA sequence

nucleosome

basic unit of chromatin

nucleosome structure

147 base pairs of DNA wrapped around 2 molecules each of histones H2A, H2B, H3, and H4, with one molecule of H1 bound to the DNA

methods by which chromatin can be altered

histone modification and nucleosome rearrangement

3 types of histone modifications

methylation, acetylation, phosphorylation

purpose of histone acetylation

creates more space between nucleosomes (by neutralizing the + charge on lysine) to allow for transcription

histone acetylation method

an acetyl group is added to lysine on the amino-terminal tail

result of an acetylated histone

chromatin is not condensed, which promotes transcription

result of a deacetylated histone

chromatin is condensed, which represses transcription

purpose of histone methylation

induces chromatin condensing and induces heterochromatin formation, which represses transcription

structural component that promoters/enhancers lack which allows them to bind transcription factors

nucleosomes

chromatin remodeling factors

protein complexes that alter contacts between DNA and histones (elongation factor)

methods used by chromatin remodeling factors

reposition nucleosomes, change nucleosome conformations, and eject nucleosomes from the DNA

epigenetic inheritance

transmission of information that is not in the DNA sequence

structures that facilitate elongation

elongation factors, the phosphorylated C-terminal domain of RNA polymerase II

DNA methylation

methyl groups are added at the 5-carbon position of a cytosine that precedes a guanine

result of DNA methylation

represses transcription in genomic imprinting

genomic imprinting

the expression of some genes depends on whether they come from the mother or the father

long noncoding RNA (lncRNA)

form complexes with proteins that modify chromatin and recruit the complexes to their target sites

miRNA

inhibit translation or degrade mRNA

function of Xist lncRNA

mediates inactivation of the X chromosome in mammals

Xist lncRNA is an example of ____ regulation

negative