DNA replication Flashcards
revision (21 cards)
What is DNA replication
DNA replication is the production of new DNA strands with base sequences identical to the base sequence of existing strands
What is DNA replication needed for ?
Reprodcution - to pass on the genetic material of a mother to a offspring the DNA must be replicated
Growth - each body cell needs to have the organisms full genetic matrial - replication during division
How is DNA replication semi-conservative?
When new DNA molecules are formed each molecule has one original strand and one newly formed strand. The newly formed strand uses the existing strand a sa template and adds complementary bases to form the new strand. The new strand will therefore be identical to the sense strand ( og strand of other molecule)
What is the function of complementary base pairing?
- Ensures accuracy in DNA replication because only the complementary bases will pair with each other
- Makes it possible to catch, clip and ocrrect mistakes in the DNA
What is Helicase and what is its function?
Helicase is an enzyme responsible for unzipping or separating the two strands of a DNA molecule for replication
It moves along the molecule and breaks the hydrogen bonds between the complimentary bases, allowing one strand to pass through its ring and one to go to the side of it.
This allows the strands to act as template and sense
What is DNA polymerase and its function?
DNA polymerase is an enzyme responsible for assembling the new strands of DNA using the original strands as templates.
It moves along the strand and adds nucelotides that are complimentary to the bases on the template strand allowing a hydrogen bond to form. Once the bases have bonded its connects the new nucleotide to the exisiting chain of nucleotides using a covalent bond between the phosphate of the new and the sugar of the old
What is a replication fork
The point at which DNA Helicase is working to unzip the strands, at which they seperate
What is a polymerase chain reaction?
A polymerase chain reaction is a temperature controlled, automated method of DNA replication
Doubles the quantity of DNA with each cycle
Can begin with very less at the start
What are primers?
Primers are 15-20 nucleotide long chains which are complementary to the start of the base sequence of the strand which needs to be copied. DNA polymerase can only attach to exisiting strands so it provides a starting point.
- Quickly bind to seperated strands to prevent them from binding again
What is Taq polymerase?
Taq is a polymerase found in hot springs that can withstand high temperatures without denaturing and add about 1000 nucelotides per minute
What are the stages of PCR
Melting - 95* C for 30-60 seconds. Breaks the bonds between the two strands but theindivudual bonds remain intact
Annealing - primers attach to the strands quickly to prevent them from binding to each other again
Elongation - 75* optimum temp for Taq polymerase which starts moving down both the strands and rapidly replicates the DNA at a speed of 1000 nucleotides per minute
What is the process of gel electrophoresis
GE allows for the separation of DNA by length due to differential migration.
Gel layer - DNA pipetted into wells - electrodes at both ends - charge run
The Pi groups are negatively charged so the DNA molecules move towards the positive electrode. The gel has pores that allow smaller fragments to move more so they move through while the larger fragments remain behind
DNA molecules of the same length will travel the same distance
RT-PCR
Rna virus - reverse transcriptase - dna
DNA is replicated using pcr ( 35 cycles)
The pcr amplifies the specific viral base sequences that are markers of covid
fluroscent markers are attached to the DNA produced if it goes above a certain level
positive test
- very sensitive requires very little RNA
- very specific can detect different strain of the virus
Paternity testing
Sample of DNA - PCR of a few STR
Gel electrophoresis makes profile
comparison of profile
What is the difference between the leading strand and the lagging strand
DNA polymerase always works 5’ to 3’
Since the two strands are antiparallel it works in opposite directions on them,
One the leading strand its goes 5’ to 3’ in the direction of the replication fork. iTs faster and more efficient
The lagging strand moves in the direction away from the fork but assembles in fragments. DNA primers keep getting added as the strands nwind and new fragments of DNA are formed called Okazai fragment
What is DNA primase?
Type of RNA polymerase. Assmebles and attaches the RNA primers which act as starting points for the DNA primase to attach nucleotides to. On the lagging strand primers are needed once every 100-200 strands.
What is DNA polyermase III
Primary polymerase. Binds to template strand at the 3’ end of the RNA primer and starts adding complementary bases in the 5’ to 3’ direction. Also proofreads
What is DNA polymerase I
Exonuclease and polymerase. Binds to the end of a Okazaki fragment and moves across the primer replacing the RNA nucleotides with DNA nucleotides. Stops when it reaches the 3’ end of the primer it cannot add 3’ to 5’ so it leaves a gap. Moves to the next fragment
What is DNA ligase?
Connects the 3’ to 5’ gap left by DNA polymerase I between a Okazaki fragment and the primer it replaced with DNA nucleotides
What is DNA proofreading?
DNA proofreading is the earliest measure of preventing mutations and errors. If it detects an incorrect pair of bases it will excise it, move back on base and replace it with a new nucleotide
What is DNA gyrase?
enzyme which follow helicase and relieves the pressure, preventing supercoiling
