DNA Replication

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  • Created by: Lotto65
  • Created on: 01-02-17 19:07
What type of replication did Crick and Watson's model of DNA suggest happened?
Semi-conservative replication
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How are the two strands of DNA separated in semi-conservative replication?
Helicase unravels it and breaks the hydrogen bonds between the bases
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What happens after the DNA has been unravelled?
New polymers of nucleotides are assembled on each of the two single strands
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What is the template strand?
The strand of DNA in which a new strand of DNA is assembled to
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How come each new strand has the same base sequence as the old strand connected to the template strand?
Complementary base pairing
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Why is it called semi-conservative replication?
Each DNA molecule consists of one new strand and one strand from the parent molecule
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How are the two strands produced in semi-conservative replication identical?
They are identical to the original parent molecule and to each other
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Name two other theorised ways of replication
Conservative replication and dispersive replication
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What happens in conservative replication?
Both parent strands remain together and another molecule is produced with two new strands
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What happens in dispersive replication?
Every molecule produced in replication has a mixture of new and old sections in both strands
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Who produced strong evidence of semi-conservative replication?
Meselson and Stahl
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What were the conditions of the Meselson and Stahl experiment?
Cultured e.coli bacteria for many generations in a medium where the only nitrogen source was 15N or 14N
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What was the purpose of growing bacteria is 15N or 14N?
So the nitrogenous bases would be made of 15N
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What is the difference physically between 15N and 14N?
14N is less dense
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What did Meselson and Stahl do with caesium chloride?
Spun it in an ultracentrifuge at 45,000 revs per min for 24hrs. Caesium ions are very heavy so sink, creating a gradient with greatest caesium concentration and density at the bottom
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What happens when you centrifuge a substance in caesium chloride solution?
The substance will be concentrated at the level of its density
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How does DNA show up in UV light?
A dark band
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What was seen after one generation?
There was an intermediate density between 15N and 14N as expected with one old and one new strand
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What was seen after two generations?
Two equal bands, one still at 14/15N and one at 14N density
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What happened in the following generations?
The 14N band became stronger and the 14/15N band weaker
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What is the name of the enzyme that unwinds the double helix and breaks the hydrogen bonds between bases?
Helicase
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What is the name of the enzyme that links nucleotides together?
DNA polymerase
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Adenine will only bind with...
Thymine
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Cytosine will only bind with...
Guanine
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Each new strand is ... to the template strand and ... to the other template strand
Complementary and identical
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True/false: Helicase splits DNA in only one place in the molecule
False - many places
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What is the function of DNA gyrase?
Prevents the enzyme suffering from uncoiling tension/ gyration
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What is another word for DNA gyrase?
Topoisomerase
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What do the stabilising proteins do?
Stop the strand twisting back up after it has been unwound/ keeps it as one strand
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What order does DNA polymerase do tasks?
1) Goes up the strand adding nucleotides 2) Comes back down cutting out mistakes 3) Goes back up adding nucleotides in the gaps
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True/false: DNA polymerase has the same active site for all its tasks
True
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What does DNA ligase do?
Joins fragments of nucleotides together
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Where does DNA polymerase start attaching nucleotides from?
The end of the RNA molecule
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What does a primer do?
Starts the process of adding nucleotides
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DNA polymerase adds nucleotides from the ... end to the ... end
5' to 3' end
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What does RNA primase do?
Makes the RNA primer by putting nucleotides together
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How many nucleotides long is the RNA primer?
10-12
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What is the function of an activated nucleotide?
Provides a source of energy to form covalent bonds
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How do activated nucleotides provide energy?
A lot of energy is released when a bond between a phosphate breaks
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How many phosphate groups in an activated nucleotide?
3
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What does DNA polymerase do in terms of the RNA primer?
Removes any uracil nucleotides and replaces it with thymine
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What are Okazaki fragments?
Where sections of nucleotides are made rather than one long strand in order to get the 5' to 3'
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Why is it called the lagging strand?
Okazaki fragments means it takes longer to attach nucleotide strands so it lags behind the leading strand
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As soon as the DNA strand splits...
Nucleotides are added
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Why is complementary base pairing important in semi-conservative replication?
Ensures the DNA molecules formed are identical in base sequence as each other and parent molecule
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Would hydrogen bonding occur if the wrong bases were trying to pair up?
No
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What do helicases use to break down the double helix?
ATP as a form of energy
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Describe the structure of one helicase
Six globular polypeptides arranged in a donut shape
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Where do the DNA strands go in the helicase described above?
One strand goes through the centre of the donut and the other on the outside
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Where are free nucleotides found?
In the area where DNA replication is occurring
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Where does DNA polymerase make covalent bonds?
Between the phosphate group of the free nucleotide and the pentose sugar of the previous one
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What prime terminal is the phosphate group?
5'
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What prime terminal is the pentose sugar?
3'
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True/ false: DNA polymerase is very accurate
True
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Other cards in this set

Card 2

Front

How are the two strands of DNA separated in semi-conservative replication?

Back

Helicase unravels it and breaks the hydrogen bonds between the bases

Card 3

Front

What happens after the DNA has been unravelled?

Back

Preview of the front of card 3

Card 4

Front

What is the template strand?

Back

Preview of the front of card 4

Card 5

Front

How come each new strand has the same base sequence as the old strand connected to the template strand?

Back

Preview of the front of card 5
View more cards

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