1.2 Replication of DNA Flashcards
Why is DNA replicated?
- daughter cells have the same number of chromosomes and so that they have the same genes.
- it happens before mitosis which is needed for growth and repair
What is the term to describe how DNA replicates itself?
semi-conservative replication
What are the 3 stages of DNA replication?
- -DNA unwinds
- hydrogen bonds between the bases break
- to form two template strands - leading strand
- primer binds at the 3’ end of the strand
- DNA polymerase adds nucleotides to the 3’ end of the primer continuously
lagging strand
- many primers attach along the strand
- as DNA polymerase can only add nucleotides to the 3’ end of the primer
- DNA polymerase adds nucleotides onto the 3’ end of the primers creating fragments
- these fragments joined together
- discontinuous process
- -The two new strands form a double helix.
- The new strands are identical to the original strands
What is the first stage of DNA replication?
- -DNA unwinds
- hydrogen bonds between the bases break
- to form two template strands
What is the second stage of DNA replication?
- leading strand
- primer binds at the 3’ end of the strand
- DNA polymerase adds nucleotides to the 3’ end of the primer continuously
lagging strand
- many primers attach along the strand
- as DNA polymerase can only add nucleotides to the 3’ end of the primer
- DNA polymerase adds nucleotides onto the 3’ end of the primers creating fragments
- these fragments joined together
What is the third stage of DNA replication?
- -The two new strands form a double helix.
- The new strands are identical to the original strands
What does the enzyme DNA polymerase do?
DNA polymerase adds DNA nucleotides, using complementary base pairing, to the 3’ end of the new DNA strand which is forming or primer.
What end of the growing strand (or primer) can DNA polymerase add nucleotides to?
the 3’ end
What is the process of replicating the leading strand of DNA?
- leading strand
- primer binds at the 3’ end of the strand
- DNA polymerase adds nucleotides to the 3’ end of the primer continuously
What is a primer and what is its role?
- short strand of nucleotides which binds to the 3’ end of the template DNA strand
- allowing DNA polymerase to add DNA nucleotides.
What is the process of replicating the lagging strand of DNA?
lagging strand
- many primers attach along the strand
- as DNA polymerase can only add nucleotides to the 3’ end of the primer
- DNA polymerase adds nucleotides onto the 3’ end of the primers creating fragments
- these fragments joined together
What are the requirements for DNA replication?
the nucleus must contain:
- DNA (to act as a template)
- Primers
- A supply of the 4 types of nucleotide
- DNA polymerase and ligase enzymes
- A supply of energy (ATP)
What is the purpose of PCR?
amplification of DNA in Vitro using complementary primers for specific target sequences
What machine does PCR take place in?
thermocycler
What is the first stage of PCR?
The DNA is heated to approximately 92-98C for a few seconds. This causes the DNA to denature and the strands to separate
What is the second stage of PCR?
The DNA is cooled to approximately 50-65C for a few seconds. This makes short primers bond to the separated DNA strands.
What is the third stage of PCR?
The DNA is heated again to between 70C and 80C for a few minutes. This allows heat tolerant DNA polymerase to replicate the DNA
repeated cycles of heating and cooling amplify the target region of DNA
What is the process of PCR?
- DNA is heated to 92-98C
- to break hydrogen bonds between bases, separating the strands - DNA is cooled to 50-65C
- allows primers to bond to target sequences - DNA is heated to 70-80C
- allow heat tolerant DNA polymerase to add nucleotides to the 3’ end of the primer
- and replicates the region of DNA - repeated cycles of heating and cooling amplify the target region of DNA
What happens with each PCR cycle?
the number of copies of the DNA doubles
What are the requirements for PCR?
- DNA sequence-template
- heat tolerant DNA polymerase-so it doesn’t denature
- primers
- supply of nucleotides of the 4 different bases
- thermocycler
Name 3 uses of PCR
- solve crimes
- Disease detection
- paternity suits
What is the enzyme used to copy DNA?
DNA polymerase
Why is one strand called the leading strand and one called the lagging strand?
- delay in the replication of the lagging strand compared to the leading strand
- lagging strand has to be synthesised in fragments
- fragments are then joined together by DNA ligase.
what is the role of DNA ligase?
To join fragments of DNA together
What temperatures are the stages of PCR carried out at?
- 92-98*C
- 50-65*C
- 70-80*C
why is heat tolerated DNA polymerase required for PCR?
to withstand repeated cycles of heating and cooling so the enzyme doesn’t get denatured
What is a primer in PCR?
short strands of nucleotides
- which are complementary to specific target sequences
- at two ends of the region if DNA to be amplified
