Trsnscription

Question 1

In 1955 Crick proposed the:

Answer 1

‘The central dogma of molecular biology’

Question 2

The central dogma of molecular DNA

Answer 2

• DNA tells to cell what to do, when to do it, how much to do it, when to stop and which cell type to do it in
• mRNA interprets the information on the information
• Protien is thus the worker

Question 3

Gene expression definition

Answer 3

The process by which information from a gene is used in the synthesis of a functional gene product.

Functional gene product: a protien of non-coding RNA (an RNA molecule will not give rise to a functional protien and has some other function

Question 4

Definition of a gene:

Answer 4

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

Question 5

The ‘gene’ (DNA) may contain sequences that:

Answer 5

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

Question 6

What is transcription

Answer 6

• when we use a double stranded DNA molecule to produce a single stranded RNA molecule

DNA-DEPENDENT RNA SYNTHESIS

Question 7

What is transcription catalysed by and how does it synthesise the mRNA

Answer 7

• the enzyme RNA polymerase
• RNA polymerase synthesises mRNA by catalysing the formation of PHOSPHODIESTER bonds between (RNA nucleotides) ribonucleotides (between the 3’ of one ribonucleotide and 5’ of another)
• RNA polymerase selects the correct nucleotides to incorporate into mRNA based on the sequence of the DNA which is being transcribed

Question 8

Which strand is mRNA trasnscribed (made) from?

Answer 8

Template strand

Question 9

Directions of the coding and template strands

Answer 9

Coding strand (5’ —-> 3’)
Template strand (3’ —-> 5’)

Question 10

3 stages of transcription

Answer 10

1. Intitiation
2. Elongation
3. Termination

Question 11

Process of initiation (3 points)

Answer 11

1. Transcription factors bind to the TATA box and other regions of the promotor (the transciption factors the recruit the RNA pol 2) -AT rich - easier to pull apart
2. RNA pol 2 binds forming transcriptional initiation complex together with the trnascription factors
3. The two DNA strands separate and RNA pol 2 starts mRNA synthesis without the need of a primer

Question 12

Elongation

Answer 12

• RNA pol 2 uses the template strand, which tuns in the 3’ —> 5’ direction, as a template, and inserts complementary RNA nucleotides in the 5’ —-> 3’ direction
• RNA floats off the strand
• More RNA pol 2 come along and start trnascription so there are multiple transcriptions of one DNA strand at once

Question 13

Where does transcription vs translation take place

Answer 13

TRanscription - nuclues
TRanslatiuon - cytoplasm

Question 14

What does / doesn’t get transcribed ANATOTOMY OF EUKARYOTIC GENES

Answer 14

Doesn’t:
- Promotor

Does:
- 5’UTR
- 3’ UTR
- Coding sequence (not one continuos sequence - broken up into little bits)

Question 15

Splicing process

Answer 15

• The transcribed region that will make up mRNA consists of ultinating exons and introns (introns are the intervening sequence)
• different genes have different numbers of introns and extrons
• To make a protein - coding sequence needs to be continuous
• splicing (pre-mRNA process removes the introns
• there are specific bases at the start and end of the introns for removal

Thus the coding sequence can now be translated

Question 16

Purpose of an intron

Answer 16

• a part of regulating gene expression
• the cell can undergo transcription ahead of time and sit in a pre - mRNA stage with the 5’g cap and a poly A tail at the end, holding it in the cell
• when the cell needs a protein - all is required is splicing and translation

Question 17

What is a coding sequence

Answer 17

• portion of a genes DNA that is translated into a protein

Question 18

What is a promotor

Answer 18

• DNA segment recognised by RNA polymerase to initiate transcription

Question 19

UTRs (UnTranslated Regioins)

Answer 19

• transcribed but (usually) not translated
• contain regulatory elements (sequences) that influence on gene expression at the transcriptional and / or translational level
• 5’ UTR facilitates the addition of the 5’G cap
• 3’ UTR facilitates the addition of the polyA tail

Question 20

What does the 5’G cap do

Answer 20

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

Question 21

What does the Poly -A tail do

Answer 21

• prevents mRNA degration and facilitates export of the mRNA from the nucleus to the cytoplasm

Question 22

Eukaryotic gene structure Elements

Answer 22

• contains non-coding DNA regions upstream and downstream of the coding sequence as well as within the coding sequence
• these non coding DNA regions can be transcribed but not translated
• these non-coding DNA elements are involved in regulating gene expression
• changes (mutations) in these non-coding gene sequences may ‘disrupt’ normal gene expression

Question 23

Cellular location of eukaryotic transcription and translation

Answer 23

Prokaryote:
- transcription and translation in cytoplasm
- transcription ciption and translation are coupled

Eukaryote:
- transcription in nuclues
- translation in cytoplasm
- transcription and translation are not coupled