Replication of DNA Flashcards
What is DNA replication?
A double helix of DNA makes an exact copy of itself.
When does the replication of DNA occur?
Immediately before mitosis.
What are the three stages of DNA replication?
- Original DNA
- Two strands separate and new bases join to either side.
- Two separate DNA molecules are formed.
During DNA replication, what allows the DNA to unwind?
The weak hydrogen bonds break between the bases.
When the DNA unzips during replication, what is the new shape called?
The two template strands produce a ‘Y-shaped replication fork’.
What are the names of the two strands during DNA replication?
Leading and lagging.
What prime end is the leading strand?
3’ end
What prime end is the lagging strand?
5’ end
Why is the strand called leading?
Complementary DNA nucleotides are added continuously to make a new strand.
Why is the strand called lagging?
Complementary DNA nucleotides make DNA fragments that must be joined together to make a new strand.
What are primers?
Short complementary sequences of nucleotides that are required at the start of a new DNA strand.
Where do primers bind?
Only to the 3’ end.
What enzyme adds the complementary nucleotides during DNA replication?
DNA polymerase
What does the enzyme DNA polymerase do?
Adds complementary nucleotides to the 3’ end and synthesises a complementary strand continuously from 5’ to 3’.
How many primers do you need for the lagging strand?
Several
How are complementary nucleotides joined to the lagging strand?
DNA polymerase adds them in fragments.
What enzymes do you need for the lagging strand?
DNA polymerase and ligase.
What is ligase used for in DNA replication?
Joining the fragments together for the lagging strand.
The formulation of which strand of DNA replication is discontinuous?
The lagging strand.
How many replication forks are formed during DNA replication?
Many
Why are there many replication forks formed at the same time during DNA replication?
To ensure the whole chromosome is replicated quickly and efficiently.
What is each replicated DNA molecule made up of?
One original strand and one new strand.
What are the 6 things that may be required during DNA replication?
- DNA template
- Free DNA nucleotides
- Primers
- DNA polymerase
- Ligase
- ATP
What is the DNA template in DNA replication?
The original strands of DNA.
What are the free DNA nucleotides used in DNA replication?
To make new complementary strands.
What are primers in DNA replication?
Needed for DNA polymerase to bind to. They are the start point of a new complementary strand or fragment.
What is DNA polymerase in DNA replication?
The enzyme that adds free nucleotides to make a complementary strand or fragment.
What is ligase in DNA replication?
The enzyme which joins the DNA of the lagging strand (like glue).
What is ATP used for in DNA replication?
The energy required for DNA replication.
What does PCR stand for?
Polymerase Chain Reaction
What is PCR?
A technique used to create many copies of a fragment of DNA in a laboratory setting.
What is the amplification of DNA?
A large quantity of the DNA fragment is made.
What do you need to start PCR?
A DNA template strand that will be amplified.
What is the first step of PCR?
The DNA sample is HEATED to 92-98C, which breaks the weak hydrogen bonds between the bases and separates the DNA strands.
What is the second step of PCR?
The DNA sample is COOLED to 50-65C, which allows short primers to bind to the separated DNA strands.
What is the third step of PCR?
The DNA sample is HEATED to 70-80C, allowing heat-tolerant DNA polymerase to replicate the DNA by adding nucleotides to the 3’ end of the original strands.
Name the heat-tolerant enzyme used in DNA replication?
DNA polymerase
What are the steps of PCR?
- Heated so hydrogen bonds break
- Cooled and primers are added
- Heated and DNA polymerase is added
- First cycle of DNA replication has now ended.
How many copies of DNA will you have after one cycle of PCR?
Two identical molecules of DNA.
How many copies of DNA would you have after 5 cycles of PCR?
2^5 = 32
Where is PCR carried out?
In a thermocycler
Why is a thermocycler useful?
Automatically carries out repeated cycles of PCR and can create millions of copies of DNA in a few hours.
What are some of the uses of PCR?
- forensics (crime scene fluids)
- paternity (check if related)
- diagnosis of genetic disorders
What are the 5 things necessary for PCR to be carried out?
- DNA template strand
- Primers
- Supply of nucleotides
- pH buffer
- Heat tolerant DNA polymerase
Within a thermocycler.
Why do you need a pH buffer during PCR?
To maintain the optimum pH for DNA replication.
