DNA Replication & Gene Expression

Question 1

What’s the structure of a nucleic acid?

Answer 1

Sugar
Nitrogenous base
Phosphate group

Question 2

What type of bond forms the backbone of DNA?

Answer 2

3’ 5’ phosphodiester links

Question 3

In prokaryotic cells:
-where does replication begin?
-which direction does replication occur?

Answer 3

-at the ‘origin of replication’ as its circular DNA
-both directions (bidirectional)

Question 4

What direction does DNA Polymerase aid replication?

Answer 4

5’ to 3’

Question 5

What occurs at the replication fork?

Answer 5

LEADING STRAND
- 5’ to 3’
LAGGING STRAND
-Okazaki fragments

Question 6

What’s the difference between coding strand, template strand and mRNA strand?

Answer 6

Coding = complimentary to template strand but DNA not RNA so T not U
Template = base strand
MRNA = complimentary to template strand using U not T

Question 7

In what type of organisms does DNA not need to be modified after translation?

Answer 7

Prokaryotes

Question 8

How is DNA modified in eukaryotic cells?

Answer 8

Splicing

Question 9

What are the 3 steps of Transcription in DNA in prokaryotic cells?

Answer 9

Initiation
Elongation
Termination

Question 10

Describe what happens in the initiation step of transcription of prokaryotic cells?

Answer 10

INITIATION
- RNA polymerase recognises promoter sites on DNA template
- sigma subunit recognises promoter sites

Question 11

What makes up RNA polymerase holoenzyme?

Answer 11

CORE ENZYMES
- 4 subunits
- 2x a 2x B
- assemble every time gene is transcribed and descramble after
SIGMA SUBUNIT
- initiation of transcription

Question 12

What occurs in the elongation step of transcription of prokaryotic cells?

Answer 12

ELONGATION
-RNA polymerase synthesises RNA that’s complimentary to template DNA
- DNA ‘unwound at forward end’ and ‘rewound at rear end’

Question 13

What occurs in the termination stage of transcription of prokaryotic cells?

Answer 13

RHO INDEPENDENT TERMINATION
- when RNA polymerase transcribes terminator region, hairpin structure forms
- hairpin structure disrupts interaction between DNA and RNA
- RNA released

RHO DEPENDANT TERMINATION
- RNA polymerase pauses when terminator region is transcribed
- Rho protein catches up from behind and causes it to detach form DNA

Question 14

Is replication faster in eukaryotes or prokaryotes?

Answer 14

Prokaryotes, less complex

Question 15

What are the roles of the following:
Pol I
Pol II
Pol III

Answer 15

I = transcribe rRNA
II = transcribe mRNA
III = transcribes tRNA

Question 16

Describe in general terms the ‘types’ of replication in eukaryotes and prokaryotes.

Answer 16

EUKARYOTES = bidirectional replication ‘bubbles’ that meet
PROKARYOTES = bidirectional with lagging strand

Question 17

Whats the problem with linear DNA replication?

Answer 17

• replication of the ends of chromosomes (telomeres)
• telomeres cannot be fully copied so end up being shortened

Question 18

What can telomerase shortening cause?

Answer 18

Cell aging/death

Question 19

What’s the purpose of telomerase?

Answer 19

-Enzyme in RNA
-extends at 3’ end to allow telomeres extension

Question 20

What are the steps in telomerase formation?

Answer 20

1. Telomerase extends at 3’ end of nearly synthesised chromosome
2. The 5’ end of telomeres is formed later from ‘lagging strand

Question 21

In what cells do telomerase operate?

Answer 21

• foetal cells
• cancer

Question 22

What occurs at the initiation stage of transcription in eukaryotic cells?

Answer 22

• promoter region recognised
• requires transcription factors to bind

Question 23

What occurs at the regulation + elongation stage of transcription in eukaryotic cells?

Answer 23

• transciption factors bind to regulatory regions
• transcription of DNA occurs

Question 24

Describe post-transciptional modification in eukaryotes.

Answer 24

1. Pre-mRNA
2. Add 5’ cap to mRNA (protect from degeneration)
3. Add poly(A) tail
4. Splicing out exons

Question 25

What’s TATA box?

Answer 25

Start of transcription