DNA Replication

Question 1

3 General features of DNA Replication

Answer 1

1.Semi conservative
2.Bidirectional
3.Occurs during S phase of cell

Question 2

Who realised DNA self replicated?

Answer 2

Watson and Crick using a parent strand and a newly synthesised strand

Question 3

What does semi conservative mean? Explain the steps

Answer 3

DNA unwound to separate template strands

Addition new nucleotides linked by covalent bonds on complementary template strand

Question 4

DNA is usually bidirectional, how do bacterial chromosomes replicate?

Answer 4

The circular DNA forms a bubble at the origin sight separating and eventually stop at the termination site.

Question 5

Eukaryotic DNA replication is similar to prokaryotes however it is more complex, how?

Answer 5

1.Eukaryotic cells contain more DNA
2.Chromosomes are linear - multiple replicons needed
3.DNA complexes with proteins (DNA packing )

Question 6

What is a replicon?

Answer 6

They are origins of replications and Eukaryotic DNA have many to speed up process of replication (2 kb/min -one chromosome takes up to 35 days)

Question 7

Short summary of the eukaryotic chromatin packaging?

Answer 7

Double stranded chromatin wound around nucleosomes with histone buckles tightening them, then nucleosomes form a 30nm fibre, fibre is further looped and compressed then coiling to form a chromatid on a chromosome,

Question 8

Nucleosomes formation summary

Answer 8

His tones are small + charged proteins (8 proteins) DNA wraps around histones to form nucleosomes

Question 9

How are nucleosomes linked?

Answer 9

Via linker DNA

Question 10

Proteins involved in replication

Answer 10

Topoisomerase
Helicase
Single stranded binding proteins (SSB)
DNA Polymerase 3
Primase
Polymerase 1
Ligase

Question 11

What does Topoisomerase do?

Answer 11

Topoisomerase unwinds double helix by snipping phosphate backbone on one strand and joins back after unwinding

Question 12

What does DNA helicase do?

Answer 12

Helicase binds to origin of replication and uses ATP to break h bonds making DNA single stranded

Question 13

What do single stranded binding proteins do?

Answer 13

They straighten the single stranded chain allowing DNA Polymerase to work

Question 14

What does DNA Polymerase 3 do?

Answer 14

Polymerase 3 catalyses the formation of phosphodiester bonds between nucleotides
(Elongation)

Question 15

What does DNA Polymerase 3 require?

Answer 15

DNA template
RNA primer (short piece of RNA)
Four dNTPs (nucleotides)

Question 16

What direction and bi product does polymerase 3 give off when joining a nucleotide?

Answer 16

5’ to 3’ direction of elongation and when a nucleotide is added 2 phosphates are give off

Question 17

Primer is 10 nucleotides long but what does it provide for the polymerase 3?

Answer 17

Provides a free 3’-OH group

Question 18

What enzyme makes primer?

Answer 18

Primase

Question 19

RNA Primer needs to be removed after elongation, how is it removed?

Answer 19

DNA polymerase removes primer and replaces it with DNA

Question 20

What does DNA Ligase do?

Answer 20

Once polymerase 3 dips, Ligase joins short fragments of DNA together

Question 21

Lagging strand and leading strand differences?

Answer 21

Lagging strand is discontinuous and leading strand is continuous