1.2 Replication of DNA Flashcards
What is ‘DNA Replication’?
When a cell makes an identical copy of their DNA at the beginning of cell division
Why is DNA replication important?
Ensures each daughter cell has an identical copy of genetic material inherited from parent cell and no genetic information is lost.
What is the function of DNA Polymerase in DNA replication?
Adds complementary DNA nucleotides to the 3’ end of the new DNA strand
Why is an original DNA strand needed?
To provide the template to be copied
What is a primer?
A short strand of nucleotides that provides a start point for DNA replication by allowing DNA polymerase to add DNA nucleotides
What is Ligase used for in DNA replication?
Joins together the DNA fragments
(from the lagging strand)
State the steps in DNA replication
- DNA is unwound, hydrogen bonds break between bases.
- A primer is needed to start replication, this binds to the start of the DNA strand.
- DNA polymerase adds complementary nucleotides to the 3’ end of the new DNA strand, they are added in a 3’ to 5’ direction.
- Replication is continuous on the leading strand but discontinuous on the lagging strand due to the antiparallel nature of DNA.
- DNA fragments on the lagging strand are joined together by DNA Ligase.
What are the two strands in DNA replication?
Leading strand and Lagging Strand
Describe the replication of the lagging strand
- The DNA molecule is unwound and the hydrogen bonds between the bases are broken.
- Multiple primers are needed to start replication, they bind along the lagging strand.
- DNA polymerase adds complementary nucleotides to the 3’ end of the new DNA strand, they are added in a 3’ to 5’ direction.
- This is a discontinuous process, so fragments are produced.
- DNA ligase joins fragments together.
Describe the replication of the leading strand
- The DNA molecule is unwound and the hydrogen bonds between the bases are broken.
- A primer is needed to start replication, this binds to the start of the DNA strand.
- DNA polymerase adds complementary nucleotides to the 3’ end of the new DNA strand, they are added in a 3’ to 5’ direction.
- This is a continuous process.
What end of the DNA strand can new nucleotides be added to?
3’
What joins DNA fragments on the lagging strand together?
Ligase
What does PCR stand for?
Polymerase Chain Reaction
What is PCR?
PCR is the amplification of DNA sequences
(makes many copies of DNA)
How does PCR amplify DNA?
Uses repeated cycles of heating and cooling to amplify the target region of DNA.
What are the three temperatures needed for PCR?
92-98°C
50-65°C
70-80°C
(you can learn any temperature in the range)
Why must DNA be heated to 92-98°C?
To denature the DNA which breaks the hydrogen bonds and sepates the DNA strands
What happens when the DNA is cooled to 50-65°C?
Allows primers to bind to the complementary DNA sequence on either side of the target sequence.
At 70-80°C what is added?
Heat-tolerant Polymerase
Why is Heat-tolerant Polymerase used in PCR?
Because it is able to withstand high temperatures (70-80°C) without being denatured
Why are two different primers required in PCR?
One primer is required for each
strand.
How is DNA separated in the lab?
Using gel electrophoresis
Give an example of a practical use of PCR
Paternity Testing
Forensics
What is a positive control for PCR?
Doing PCR with a known sample of DNA, expected result is known
What is a negative control for PCR?
Doing PCR with a key factor missing (such as removal of DNA Polymerase) to prove no contamination
After each cycle of PCR how much more DNA is present?
Double the original amount
If a scientist did 5 cycles of PCR, how many copies of the DNA would they have?
(we always assume unless it says that we start with 1 copy of DNA)
32
