Deck 16: Control of Gene Expression in Eukaryotes

Question 1

Sensitivity to DNase I digestion indicates that transcribed DNA assumes an open configuration before transcription. Chromatin structure can be altered by modifications of histone proteins, by chromatin-remodeling complexes that reposition nucleosomes, and by the methylation of DNA.
-What are some of different processes that affect gene regulation by altering chromatin structure?

Answer 1

Three general processes are the modification of histone proteins (e.g. methylation and acteylation of histones), chromatin remodeling, and DNA methylation.

Question 2

Epigenetic effects-stable alterations to gene expression that are not caused by changes in the DNA base sequence-are frequently associated with changes in chromatin structure. The epigenome is the genomewide pattern of epigenetic changes possessed by an individual organism.

-Which is not a mechanism of pigenetic change?

A) DNA methylation
B) Alteration of a DNA base sequence in a promoter
C) Histone actylation
D) Nucleosome repositioning

Answer 2

Alteration of a DNA base sequence in a promoter

Question 3

Transcriptional regulatory proteins in eukaryotic cells can influence the initiation of transcription by affecting the stability or assembly of the basal transcription apparatus. Some regulatory proteins are activators and stimulate transcription; others are repressors and inhibit initiation of transcription.

-Most transcriptional activator proteins affect transcription by interacting with

A) introns.
B) the basal transcription apparatus.
C) DNA polymerase.
D) nucleosomes.

Answer 3

the basal transcription apparatus.

Question 4

Some regulatory proteins bind to enhancers, which are regulatory elements that are distant from the gene whose transcription they stimulate. Insulators are DNA sequences that block the action of enhancers.
-How does the binding of regulatory proteins to enhancers affect transcription at genes that are thousands of base pairs away?

Question 5

The stability of mRNA influences gene expression by affecting the amount of mRNA available to be translated. The stability of mRNA is affected by the 5' cap, the poly(A) tail, the 5' UTR, the coding section, and sequences in 3' UTR.

-How does the poly(A) tail affect stability?

Question 6

RNA silencing is initiated by double-stranded RNA molecules that are cleaved and processed. The resulting siRNAs or miRNAs combine with proteins to form complexes that bind to complementary sequences in mRNA or DNA. The siRNAs and miRNAs affect gene expression by cleaving mRNA, inhibiting translation, altering chromatin structure, or triggering RNA degradation.

-In RNA silencing, siRNAs and miRNAs usually bind to which part of the mRNA molecules that they control?

A) 5' UTR
B) Segment that encodes amino acids
C) 3' poly(A) tail
D) 3' UTR