Lectures 1.10

Question 1

What is the Histone Code ?

Answer 1

hypothesis that the transcription of genetic information encoded in DNA is in part regulated by chemical modifications to histone proteins, primarily on their unstructured ends.

Question 2

What processes does the histone code influence?

Answer 2

Transcription and translation (??)

-Gene activation (??)

Question 3

Heterochromatin

Answer 3

very condensed structure with few transcribed genes

Question 4

gene silencing

Answer 4

regulation of gene expression in a cell to prevent the expression of a certain gene

Question 5

How is methylation important in gene silencing?

Answer 5

• methylation can lead to gene silencing
• regions with methylation of cytosine in high frequencies are called CpG islands
• methylation changes with age, time, ect.

Question 6

What is the role of XIST in gene silencing?

Answer 6

X-inactive specific transcript

• is expressed only in inactive X chromosomes
• XIST RNA “coats” the chromosome from which it was produced, down regulating gene expression

Question 7

What are the differences in the roles of basal transcription factors, transactivators, and coactivators?

Answer 7

• all Pol II promoters need basal transcription factors to assemble Pol II at the promoter (but this is not sufficient for transcription)
• transactivators will bind to DNA and recruit coactivators (and remodeling complexes)
• Histones will be modified, structure changes, and RNA pol. complex will be loaded on to the chromatin and transcription can start.

Question 8

Transactivators are described as being modular. What are some examples of modules involved in transcriptional regulation discussed in lecture?

Answer 8

• Gal4: zinc-finger DNA binding domain, dimerized
• SP1: zinc-finger DNA binding domain, glutamine rich activation domain
• CTF1: basic residue rich DNA binding domain, proline rich activation domain

Question 9

How does RNA interference modulate mRNA levels?

Answer 9

• mRNA gene expression is regulated by microRNA

- miRNA work through RISC complexes to either degrade mRNA or inhibit translation

Question 10

euchromatin

Answer 10

more open structure, contains activity transcribed genes

Question 11

Remodeling complex

Answer 11

changes chromatin structure

• requires ATP
• alters the position of histones making DNA accessible

Question 12

Chromatin remodeling

Answer 12

alters histones in chromatin to make DNA accessible for the binding of the protein complex
-once chromatin is remodeled, state is maintained until modified by another complex

Question 13

Histone modification

Answer 13

large protein complexes recognize nucleosomes and histones in chromatin

• they change post translational modifications
• modifications have meaning and are read by other protein complexes which can remodel chromatin again and change properties

Question 14

What histone modification promotes gene activation?

Answer 14

acetylation of Lysine 14 in H3 promotes chromatin being transcriptionally active

Question 15

Leucine zipper

Answer 15

leucine zipper proteins form coiled-coil homo-dimers or heterodimers which bind to DNA through a DNA binding domain