Cell Biology- Hejmadi3- DNA replication

?
What are the 4 requirements for DNA to be the genetic material?
1. Must carry information -genetic code, which must be stable 2. Must replicate -DNA replication 3. Must allow for information to change -mutation 4. Must govern the expression of the phenotype -gene function
1 of 26
Define DNA replication
The process of duplication of the entire genome prior to cell division
2 of 26
What is the significance of DNA replication?
It - preserves integrity of the genome in successive generations - replication rates vary (slower in eukaryotes due to DNA stored in very condensed form)
3 of 26
Describe the basic 3 step process of DNA replication
1.Initiation -Proteins bind to DNA and open up double helix 2.Elongation -Proteins connect the correct sequences of nucleotides into a continuous new strand of DNA 3.Termination Proteins release the replication complex
4 of 26
What are the 6 basic features of DNA replication?
Semi-conservative, starts at the origin, can be uni or bi-directional, semi-discontinuous, synthesis in 5'-->3', RNA primers required
5 of 26
What is meant by DNA replication being semi-conservative?
the two daughter molecules will have one parental strand and one newly synthesized strand of DNA.
6 of 26
What were the two other proposed models of DNA replication?
1)conservative model- 2 parental strands are kept together and so are 2 newly synthesized strands. 2)dispersive model, the strands of the daughter molecules contain pieces of the parental and pieces of newly synthesized DNA
7 of 26
Who proved the correct model was semi-conservative and how?
Matt Meselson and Frank Stahl- by growing bacteria in different isotopes of nitrogen (ensure you can describe this experiment in detail - cell bio lecture 3 p2-3)
8 of 26
Initiator proteins identify specific base sequences on DNA called ...?
sites of origin. (where replication starts)
9 of 26
How many sites of origin do a)prokaryotes b)eukaryotes have?
a) single b)multiple
10 of 26
What does DNA replication being uni or bi-directional refer to?
that replication forks can move in the same or opposite directions (usually opposite and DNA helices elongate from each origin until they eventually join echother- circular DNA)
11 of 26
What does DNA replication being 'semi-discontinuous' refer to?
Leading strand synthesises continuously in direction of replication fork movement, whilst lagging strand synthesises fragments(discontinuous) in the opposite direction
12 of 26
What are these fragments known as? by what and when are they joined together?
Okazaki fragments- sometime after their synthesis in a reaction catalysed by DNA ligase
13 of 26
How do we know that DNA synthesis always occurs in the 5'-->3' direciton?
Due to pol1's proofreading capabilities (it can edit a DNA chain as it is synthesized so as to correct its mistakes. )
14 of 26
What 3 important factors does DNA polymerase require to work?
dNTPs, a template strand, a primer
15 of 26
Why is a template strand necessary?
to line up a new nucleotide in the right order so that the dNTPs can pair by complementary base pairing with the pairs on existing strand.
16 of 26
What is a primer?
a place where the DNA molecule is already double stranded- has a 3’ end available on it- DNA polymerase acts by adding dNTPs onto that 3’ end.
17 of 26
Describe the synthesis of the new strand briefly
The phosphorus in the 5’ phosphate group of dNTP will form a covalent bond with the oxygen in the 3’ hydroxyl group of the primer. In this process 2 phosphates and one oxygen are lost (hydrolysis), which releases energy to drive the reaction
18 of 26
What bond is formed and what does it do?
A phosphodiester bond, from 5' to 3', hlds the new nucleotide onto the end of the strand
19 of 26
Describe what happens if DNA polymerase makes a mistake.
the polymerase activity is inhibited and the 3’→5’ exonuclease removes the incorrect nucleotide. The polymerase activity then resumes DNA replication.
20 of 26
What does DNA polymerase require in order to proceed adding new bases along the template?
a 3'OH group
21 of 26
So What does RNA polymerase do?
creates a short temporary primer on the DNA template. (it requires a template like DNA polymerase does not need the -OH group of previous nucleotide)
22 of 26
After a short RNA primer sequence has been created on the DNA template strand...
the RNA polymerase falls off and DNA polymerase can add onto the hydroxyl group (-OH) of the RNA primer and start synthesizing from there. The RNA is removed shortly after the DNA synthesis starts.
23 of 26
Describe the function these core proteins at the replicaiton fork a)Topoisomerases b)Helicases c)Primase d)Single strand binding proteins
a) Prevents torsion by DNA breaks b) separates 2 strands c) RNA primer synthesis d) prevent reannealing of single strands
24 of 26
e)DNA polymerase f)Tethering protein g)DNA ligase
e )synthesis of new strand f) stabilises polymerase g) seals nick via phosphodiester linkage
25 of 26
What is the difference between DNA polymerase I and III?
a)III- after RNA polymerase has layed down an RNA primer, DNA polymerase III lays down new DNA. b)I-replaces RNA primers layed down by RNA polymerase with DNA
26 of 26

Other cards in this set

Card 2

Front

Define DNA replication

Back

The process of duplication of the entire genome prior to cell division

Card 3

Front

What is the significance of DNA replication?

Back

Preview of the front of card 3

Card 4

Front

Describe the basic 3 step process of DNA replication

Back

Preview of the front of card 4

Card 5

Front

What are the 6 basic features of DNA replication?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA replication resources »