7.2 Transcription and Gene Expression

Question 1

Promoter

Answer 1

non-coding DNA
sequence located near a gene
it is the binding site of RNA polymerase (the enzyme that catalyzes the formation of the covalent bond between nucleotides during the synthesis of RNA)
the promoter is NOT transcribed

Question 2

Enhancers

Answer 2

regulatory sequences on the DNA which increase the rate of transcription when proteins bind to them
can be distant from the promoter

Question 3

Silencers

Answer 3

regulatory sequences on the DNA which decrease the rate of transcription when proteins bind to them
can be distant from the promoter

Question 4

promoter-proximal elements

Answer 4

series of sequences that are nearer to the promtoer and binding of proteins to them is also necessary to initiate transcription

Question 5

Morphogens

Answer 5

the embryo contains an uneven distribution of chemicals called morphogens
concentrations of morphogens affect gene expression contributing to different patterns of gene expression and thus different fates of the embryonic cells depending on their position in the embryo

Question 6

Chemical modification of histone tails

Answer 6

can either activate or deactivate genes by decreasing or increasing the accessibility of the gene to transcription factors

• addition of an acetyl group
• addition of a methyl group
• addition of a phosphate group

Question 7

Methylation patterns

Answer 7

methylation of histones can promote or inhibit transcription
direct methylation of DNA tends to decrease gene expression

Question 8

Chemical Modifications That Prevent Transcription

Answer 8

silent (condensed) chromatin
methylated cytosines
deacetylated histones

Question 9

Chemical Modifications That Allow Transcription

Answer 9

active (open) chromatin
unmethylated cytosines
acetylated histones

Question 10

Transcription

Answer 10

initiation:
- begins near promoter
- RNA polymerase binds and DNA is unwound by the RNA polymerase forming an open complex
elongation
- RNA polymerase slides along the DNA synthesizing a single strand of RNA
termination

Question 11

Post-transcriptional modification

Answer 11

• RNA splicing:
  interspersed throughout the mRNA are sequences that will not contribute to the formation of the polypeptide (introns/intervening sequences)
  must be removed
  (the remaining coding portions of the mRNA are called exons)
• addition of 5’ cap and poly-A tail

Question 12

Alternative splicing

Answer 12

a process during gene expression whereby a single gene codes for multiple proteins (multiple exons)