Chapter 3

Question 1

What are the steps of transcription?

Answer 1

1. Transcription factor binds to the TF-response element
2. RNA polymerase binds to TATA-box
3. Transcription starts

Question 2

What is a response element?

Answer 2

Specific DNA sequences that can be recognized by transcription factors

Question 3

What domins do all Transcription factors have?

Answer 3

1. DNA-binding domain

2. Transcriptional activation domain (binds to Polymerase II)

Question 4

What do some TFs have, but not all?

Answer 4

1. Dimerization domain

2. Ligand-bindng domain

Question 5

What kinds of DNA binding domains are there?

Answer 5

1. Zinc finger
2. Helix-loop-helix
3. Helix-turn-helix
4. Leucine zipper

Question 6

What is the role of Ligand-binding domains?

Answer 6

it is a mechanism to regulate the activity of TFs. Some TFs repress transcription in the absence of some ligands

Question 7

What is the role of TF dimers?

Answer 7

Dimers can have various combinations of transcriprion factors, giving rise to different activation properties

Question 8

What technique could be used to study TF binding to DNA?

Answer 8

EMSA (Electrophoretic mobility shift assay)

- Difference between DNA/protein complex and free probe

Question 9

What kind of modifications can histones undergo?

Answer 9

1. Acetylation
2. Methylation
3. Phosphorylation
4. Ubiquitination

Question 10

Are histone modifications reversible?

Answer 10

Yes

Question 11

What effect does acetylation have on gene transcription?

Answer 11

Activatory effect

Question 12

what effect does methylation have on gene transcription?

Answer 12

Repressing effect

Question 13

What kind of histone modification can promote cancer?

Answer 13

1. High HDAC (histone deacetylase) activity found near tumor-suppressor genes
2. High HAT (histone acetyl transferase) activity found near oncogones

Question 14

What effect does methylation have on DNA?

Answer 14

Repressing effect

Question 15

Where does methylation of the DNA happen?

Answer 15

In a C preceding a G on a strand. There are CpG islands near gene promoters that can be methylated.

Question 16

How does DNA methylation inhibit transcription?

Answer 16

1. Prevent TFs from binding to the DNA

2. Recruits HDAC to remove acetyls from histones and make chromatin more compact

Question 17

Which enzyme transfers methyl groups to DNA?

Answer 17

DNMT (DNA methyl transferase)

Question 18

What is the role of miRNA?

Answer 18

It is a post-transcriptional regulator of gene expression

Question 19

How does miRNA control gene transcription?

Answer 19

1. Repressing translation

2. destabilisation and cleavage of mRNA

Question 20

what is the function of a T-loop?

Answer 20

A T-loop is used to prevent the DNA endings from being seen as strand breaks.

Question 21

what are the components of a telomerase?

Answer 21

hTERT and hTR

Question 22

Which cells normally express telomerase?

Answer 22

Embryonic stem cells and germ line cells

Question 23

what could be a reason for telomere shortening?

Answer 23

1. End replication problem

2. Oxidative stress

Question 24

What are some challenges in targeting telomerase a sa therapeutic option

Answer 24

1. Inhibitors of this enzyme are very rare and toxic
2. Cancers might have already produced cells with long telomers, so division can still go on for some time
3. Cancer cells may be resistant to the telomerase inhibitors