DNA replication Flashcards
DNA
-Deoxyribonucleic Acid.
-It is the molecule of inheritance and can direct it’s own replication.
-The DNA forms the genetic code in its sequence
-The sequence of bases determines the organisms genotype and the structure of it’s proteins.
What are the components of DNA
Called Nucleotide
-Phosphate
-Base
-Deoxyribose Sugar
Bond which joins bases
hydrogen bond
What is the DNA molecule’s sugar-phosphate backbone
-A strong bond forms between the phosphate of one nucleotide and the deoxyribose sugar on another nucleotide.
-Nucleotides joined together in a long permanent strand.
Anti-parallel
The leading strand is organised from the 5’ to the 3’ end. The lagging strand is organised from the 3# end to the 5’ end.
Replication of DNA
Prior to cell division DNA has to be replicated by an enzyme called DNA Polymerase.
DNA Polymerase
-DNA Polymerase is the enzyme that adds DNA nucleotides, using complementary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming.
-DNA polymerase needs primers to start replication.
Primers
A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing DNA polymerase to add DNA nucleotides.
Differences in strands
-Since DNA polymerase can only add nucleotides in one direction the two strands replicate slightly different.
-Leading strand – replicates continuously.
-Lagging strand - replicates in fragments .
This is because replication happens in a 5’ to 3’ direction
DNA Replication
Stage 1-
The DNA double helix molecule unwinds
Stage 2-
The weak hydrogen bonds between the complimentary base pairs breaks, allowing the two strands to seperate forming two template strands
Leading strand will replicate continuously
Stage 3-
A primer must be present,before the free DNA nucleotides can be added
Stage 4-
Individual nucleotides become aligned with their complimentary base on the template strand and form hydrogen bonds
The lagging strand will replicate in fragments
Stage 3-
The strand is replica ted in fragments, with each fragment having to be primed with primers
Stage 4-
Individual nucleotides become aligned with their complimentary base on the template strand at the 3’ end of the primer forming hydrogen bond
Stage 5-
The DNA polymerase binds the individual nucleotides together forming a sugar phosphate back-bone.
Stage 6-
The primers are replaced with DNA. The fragments of DNA are joined by DNA Ligase.
List of requirements of DNA replication
-DNA(as a template)
-Primers
-A supply of the four type of DNA nucleotide
-Appropriate enzymes(eg. DNA polymerase and ligase
-A supply of ATP
PCR
-PCR amplifies DNA using complimentary primers for a specif target sequence
-PCR is repeated cycles of heating and cooling to amplify a target region of DNA
PCR Primers
In PCR primers are shorts strands of nucleotides which are complementary to specific target sequences at the two end of the region of DNA to be amplified.
Stages of PCR
Stage 1-
DNA heated to between 92 degrees and 98 degrees to seperate the two strands
Stage 2-
It is cooled to between 50 degrees and 65 degrees to allow the primers to bind to target sequence
Stage 3-
Then heated to between 70 degrees and 80 degrees for heat tolerant DNA polymerase to replicate the region of DNA
PCR application
-solve crime
-diagnose genetic disorders
-settle paternity suits
