biol 3250 - chapter 15 and 16

just like in bacteria, eukaryote gene expression can be regulates in ?

transcription, translation or posttranslationally

general transcription factors (TFIID, TFIIB, TFIIF, TFIIH) and mediator

required for the binding of the RNA polymerase to the core promoter and its progression to the elongation stage

• necessary for basal transcription

regulatory transcription factors

serve to regulate the rate of transcription of target genes

• influence the ability of RNA polymerase to begin transcription of a particular gene

a regulatory protein that increases the rate of transcription is called ?

the sequence that binds it is called ?

1. activator

2. enhancer

a regulatory protein that decreases the rate of transcription is called ?

the sequence that binds it is called ?

1. repressor

2. silencer

motifs are also found in ?

bacteria

most response elements are located within a few hundred nucleotides ?

upstream of the promoter

• some are found at other sites

  • several thousand nucleotides away

  • downstream of the promoter

  • within introns

regulatory transcriptional activator and repressor proteins typically act at ?

the general transcriptional factor (TFIID)

the carboxyl-terminal domain of RNA polymerase has to be ?

a phosphorylated for it to be active

mediator influences the ability of TFIIH to phosphorylate the ?

carboxyl terminal domain (CTD) of RNA polymerase II

three common ways the function of regulatory transcription factors can be modulated

1. binding of a small effector molecule

2. protein-protein interactions

3. covalent modification

the three-dimensional packing of chromatin is an important parameter affecting gene expression in eukaryotes, chromatin is ?

a very dynamic structure that can alternate between two conformations

closed conformation

chromatin is very tightly packed

transcription may be difficult or impossible

open conformation

chromatin is accessible to transcription factors

transcriptions can take place

chromatin remodeling complexes change chromatin structure in three ways

1. change in the position of nucleosomes

2. eviction of histone octamers

3. change in the composition of nucleosomes

a nucleosome is a histone octamer composed of ?

two 3H histone proteins

two 4H histone proteins

two H2A histone proteins

two H2B histone proteins

• wrapped around DNA

• the H1 histone protein is not apart of the nucleosome, but serves as a linker between nucleosomes

the H2A, H2B, H3 and H4 can be ?

(the H1 histone can also be ?)

acetylated

methylated

phosphorylated

DNA is less tightly bound to the histone proteins when they are ?

acetylated

DNA methylation also occurs in ?

bacteria

both adenine and cytosine bases can be ?

methylated

DNA methylation usually inhibits ?

gene transcription

epigenetic change is ?

change in gene expression that is permanent over the course of one’s life but not over the course of multiple generations

epigenetic changes do not involve ?

changes to the sequence of an individual’s DNA

epigenetic inheritance involves epigenetics changes that are passed from ?

parent to offspring

• genomic imprinting

• x-chromosome inactivation

epigenetic changes are primarily caused by ?

DNA methylation

histone modification

histone remodeling

epigenetic changes may be ?

cis or trans

cis-epigenetic changes are ?

maintained at a specific site

trans-epigenetic changes are ?

maintained by diffusible factors

• transcription factors

euchromatin

regions that are not stained during interphase

• transcriptionally active

• holds a central position in the nucleus

heterochromatin

regions that are stained throughout the cell cycle

• greater level of compaction

• not transcriptionally active

• localized along periphery of the nucleus; attached to the nucleus lamina

heterochromatin is considered more ?

compacted than euchromatin

many changes that occur during development are maintained by ?

epigenetic regulation

• genomic imprinting

• x-chromosome inactivation

• formation of specific cell types and tissues

genomic imprinting

form of gene regulation in which an offspring expresses the copy of a gene from one parent but not both

x-chromosome inactivation

occurs during embryogenesis in female mammals

prior to XCI, the Tsix gene is expressed on both x chromosomes

expression of Tsix RNA results in ?

an active X chromosome

expression of Xist RNA results in ?

an inactive X chromosomes that becomes a barr body

two types of competing protein complexes are key regulators of epigenetic changes that occur during development and produce certain cell types and tissues

trithorax group (TrxG)

polycomb group (PcG)

trithorax group (TrxG)

involved with gene activation

polycomb group (PcG)

involved with gene repression

paramutation is the interaction between two alleles at the ?

single locus where one allele induces a change in the other allele

allele that has paramutation capacity is ?

paramutagenic

allele that had been altered is ?

paramutable

environmental agents can cause ?

epigenic changes