Lecture 3- Gene organisation and transcription I

Question 1

What are Housekeeping Genes?

Answer 1

Genes expressed in all cells, needed for normal cell function and viability.

Question 2

What is RNA?

Answer 2

Ribo Nucleic Acid, it is the initial product of gene expression to make proteins. It can act as the template of protein translation.

Question 3

What are the differences between RNA and DNA?

Answer 3

• RNA: single-stranded, shorter, A-U, ribose sugar

- DNA: double-stranded, longer, A-T, deoxyribose sugar

Question 4

What happens when cells specialise?

Answer 4

All cells contain the same DNA and genes but different genes are switched on and off so they make different proteins.

Question 5

Outline what happens during transcription…

Answer 5

1) DNA helix unwinds
2) Ribonucleotides base pair with DNA bases on antisense strand
3) RIbonucleotide bases are joined by phosphodiester bonds.
4) RNA chain grows one base at a time in a 5’-> 3’ direction

Question 6

Which enzyme carries out gene transcription?

Answer 6

RNA polymerase

Question 7

What is a transcription factor?

Answer 7

A special gene regulatory protein which binds to DNA and regulates gene activity.

Question 8

What is a gene promoter?

Answer 8

The DNA sequence at which the transcription complex binds.

Question 9

What do transcription activators do?

Answer 9

Activate gene expression

Question 10

What do transcription repressors do?

Answer 10

Suppress gene expression

Question 11

What are the three different types of RNA polymerases and what do they transcribe?

Answer 11

1) RNA Polymerase I - rRNA genes
2) RNA Polymerase II- transcribes genes encoding proteins into mRNA
3) RNA Polymerase III- tRNA and 5S RNA genes

Question 12

What is found in the gene promoter region of a gene?

Answer 12

• A transcription factor binding site

- The TATA sequence

Question 13

What is the purpose of the TATA DNA sequence?

Answer 13

Found in the gene promoter region, it specifies the initiation point for transcription by RNA Pol II.

Question 14

1) What is the first thing to bind to the TATA sequence

2) What does it contain to help bind?

Answer 14

1) TF IID

2) TATA Binding Protein (TBP) and TBP Accessory Factors (TAF)

Question 15

After TF IID binds to the TATA sequence what happens

Answer 15

• Partially unwinds the DNA helix, widening the minor groove to allow extensive contact with bases within the DNA
• Unwinding is asymmetric w.r.t. the TBP-TATA complex, assuring transcription is unidirectional

Question 16

What binds to TF IID and why?

Answer 16

• TF IIA and TF IIB bind with TF IID.

- This is because TF IIB can bind with both TF IID and RNA Pol II

Question 17

What binds to TF IIA and TF IIB

Answer 17

RNA Pol II which is bound to TF IIF

Question 18

What binds to RNA Pol II and why?

Answer 18

• TF IIE, TF IIH and TF IIJ

- TF IIH promotes further unwinding of the DNA helix to facilitate RNA synthesis by RNA Pol II.

Question 19

What is the purpose of the Basal Transcription Complex?

Answer 19

• Allows RNA Pol II to be phosphorylated and then engage in transcription
• Produces BASAL level of transcription in the absence of other Transcription Factors

Question 20

What are the two ways that transcription factors can work?

Answer 20

1) Bind to transcription factor binding sites and ‘bend’ DNA. They interact with each other and the Basal Transcription Complex.
2) Can remodel chromatin by using proteins with enzymatic activity to modify histones

Question 21

How do you get gene expression?

Answer 21

Hyperacetylation- histone tails, which extend from nucleosomes, are acetylated. This causes the core DNA to be coiled less tightly

Question 22

How do you get gene repression?

Answer 22

Hypoacetylation- histone tails, are deaceylated so the DNA is closed and coiled tightly.

Question 23

What are the major determinants of Transcription Factor expression?

Answer 23

1) Cell Lineage
2) External Signals- Hormones, Growth Factors, Mechanical Stress, Heat, Light etc.
3) Cancers- abnormal transcription factor expression