Gene Expression - Transcription

Question 1

What is gene expression?

Answer 1

The process by which the information from a gene is used in the synthesis of a functional gene product (which can be a protein or a non-coding RNA)

Question 2

How many protein coding genes are there roughly?

Answer 2

~20,000

Question 3

What is a gene (for the purposes of this course)?

Answer 3

A defined region (sequence) of DNA that produces a type of RNA molecule that has some function

Question 4

What sequences could a gene (DNA) contain?

Answer 4

• responsible for the regulation of the synthesis of RNA
• that produce the RNA
• responsible for further processing of the RNA

Question 5

What is transcription?

Answer 5

When we use a double stranded DNA molecule to produce a single stranded RNA. This is catalysed by an enzyme called RNA polymerase.

Question 6

How does RNA polymerase synthesise mRNA?

Answer 6

By catalysing the formation of phosphodiester bonds ribonucleotides.
RNA polymerase selects the correct nucleotides to incorporate into mRNA based on the sequence of the DNA that is being transcribed.

Question 7

Which DNA strand is transcribed?

Answer 7

mRNA is transcribed (made) from the TEMPLATE strand - (so it is the same as the coding strand but just in RNA form. is called the RNA transcript strand). The template strand is read in the 3’ to 5’ direction so that the new strand is synthesized in the 5’ to 3’ direction.

Question 8

What are the three stages of transcription?

Answer 8

1. Initiation
2. Elongation
3. Termination (WON’T be looking at this in this course)

Question 9

What happens in the Initiation stage of transcription?

Answer 9

• Transcription factors bind to the TATA box and other regions of the promoter
• RNA pol II binds, forming a transcriptional initiation complex together with the transcription factors
• The two DNA strands separate and RNA pol II starts mRNA synthesis without the need of a primer (because it has its own internal 3’ OH group)

Question 10

What is the promoter region?

Answer 10

A particular section of DNA to which proteins bind

Question 11

What is a TATA box?

Answer 11

It is a DNA sequence made of A’s and T’s that indicates where a genetic sequence can be read/decoded. It is a type of promotor region that specifies to other molecules where transcription begins.

Question 12

What happens in the Elongation stage of Transcription?

Answer 12

RNA pol II used the template strand, which runs in the 3’ to 5’ direction, as a template and inserts complementary RNA nucleotides in the 5’ to 3’ direction

Question 13

Transcription happens where in the cell?

Answer 13

The nucleus

Question 14

What is a coding sequence?

Answer 14

A portion of gene’s DNA that is translating into a protein

Question 15

What is a promotor?

Answer 15

DNA segment recognised by RNA polymerase to indicate transcription

Question 16

What is a UTR?

Answer 16

Untranslated Regions.
- They are transcribed but usually not translated.
- They contain regulatory elements (sequences) that influence on gene expression at a transcriptional and/or translational level.
- 5’ UTR facilitates the addition of the 5’ cap
- 3’ UTR facilitates the addition of the poly-A tail

Question 17

What is a 5’ cap?

Answer 17

It prevents mRNA degradation, promote intron excision and provides a binding site for the small ribosomal subunit

Question 18

What is a poly-A tail?

Answer 18

Prevents mRNA degradation and facilitates export of the mRNA from the nucleus to the cytoplasm

Question 19

What is an intron?

Answer 19

They are sequences in-between the coding sequence (they break up the coding sequence) that regulate transcription. They are responsible fro separating genes in DNA and have portions that act as transcription promotor regions

Question 20

Location of transcription. Eukaryotic cell vs prokaryotic cell.

Answer 20

Eukaryotic = in nucleus
Prokaryotic = in cytoplasm