7.5 Control of Gene Expression in Eukaryotes [HY]

Question 1

Cis Regulators

Answer 1

• The DNA regulatory base sequences (such as promoters, enhancers, and response
  elements; (called Cis b/c) they are in the same vicinity as the gene
  they control.

Question 2

Trans Regulators

Answer 2

• Transcription factors have to be produced and translocated back to the nucleus; (called treg b/c)they travel through the cell to their point of action

Question 3

Transcription factors

Answer 3

• transcription-activating proteins that search the
  DNA looking for specific DNA-binding motifs. Transcription factors tend to have two recognizable domains: a DNA-binding domain and an activation domain

Question 4

DNA-binding domain

Answer 4

• binds to a specific nucleotide sequence in the promoter region or to a DNA response element (a sequence of DNA that binds only to specific transcription factors) to help in the recruitment of transcriptional machinery

Question 5

Activation domain

Answer 5

• allows for the binding of several transcription factors and other important regulatory proteins, such as RNA polymerase and histone acetylases, which function in the remodeling of the chromatin structure

Question 6

Signal molecules that bind to specific receptors

Answer 6

• cyclic AMP (cAMP), cortisol, and estrogen

Question 7

What does the distance between the enhancer and promoter regions mean?

Answer 7

• that DNA often must bend into a hairpin loop to bring these elements together spatially

Question 8

Where can enhancer regions be located?

Answer 8

Enhancer regions in the DNA can be up to 1000 base pairs away from the gene they regulate and can even be located within an intron, or noncoding region, of the gene.

Question 9

Where can upstream promoter elements found?

Answer 9

upstream promoter elements must be within 25 bases of
the start of a gene

Question 10

How many copies of genes can be replicated?

Answer 10

• Genes can be duplicated in parallel by opening the gene with helicases and permitting DNA replication only of that gene; cells can continue replicating the gene until hundreds of copies of the gene exist in parallel on the same chromosome

Question 11

How is DNA packaged in the nucleus?

Answer 11

• as chromatin, which requires chromatin remodeling to allow transcription factors and the transcriptional machinery easier access to the DNA
• Remodeling of the chromatin structures regulates gene expression levels in the cell.

Question 12

Histone acetylases

Answer 12

• These proteins are involved in chromatin remodeling
• they acetylate lysine residues found in the amino terminal tail regions of histone proteins

Question 13

Acetylation

Answer 13

• Occurs on histone proteins and decreases the positive charge on lysine residues and
  weakens the interaction of the histone with DNA, resulting in an open chromatin conformation that allows for easier access of the transcriptional machinery to the DNA.

Question 14

DNA methylases

Answer 14

• add methyl groups to cytosine and adenine nucleotides; methylation of genes is often linked with the silencing of gene expression
• Heterochromatin regions of the DNA are much more heavily methylated, hindering access of the transcriptional machinery to the DNA