DNA Replication Flashcards
Where is DNA Replication Required In?
Growth
Reproduction
Tissue Replacement
Leading and Lagging Strand
Leading Strand: 3’ to 5’ Direction
Lagging Strand: 5’ to 3’ Direction
Factors that Determine Movement of Molecules in Gel Electrophesis
Charge: The more negatively charged, the farther fragments travel
Size: The smaller the fragment, the farther they move
PCR
PCR (Polymerase Chain Reaction) is used to amplify small quantities of DNA to produce multiple copies of DNA
This is usually done by DNA Replication
PCR Requirements
A sample of DNA
Taq Polymerase: A thermostable DNA polymerase that is capable of joining together tens of thousands of complementary nucleotides to form new DNA (extracted from Thermus Aquaticus, a bacteria that lives in hot springs therefore can handle heat)
Primers: Short lengths of RNA that attach to separated strands of DNA, also provide starting points for replication
Nucleotides: A T C G which are building blocks
Thermal Cycler: A computer controlled machine which cycles through high and low temperatures over a period of time to control replication
Process of Gel Electrophesis
A sample of DNA is extracted and amplified using PCR
DNA gets cut into different lengths and placed in the agarose gel at the negative electrode
A fluorescent marker is added so fragments can be seen
An electrical current is passed across the gel, thus making negatively charged DNA move towards the positive side, with the distance they move depending on their mass
Differences with Leading and Lagging Strand
Leading has no Okazaki Fragments
Lagging has Okazaki Fragments
Leading runs from 3’ to 5’ direction
Lagging runs from 5’ to 3’ direction
Leading is continuous
Lagging is discontinuous
Leading doesn’t need Ligase
Lagging needs Ligase
Leading replicates towards replication fork
Lagging replicates away from replication fork
Importance of Complementary Base Pairing in DNA Replication
In replication, the original strands are used as templates, allowing complementary bases to be added through complementary base pairing
Strand formed on template strand is identical to the other template strand
Advantages of PCR
Extremely rapid as 100 billion copies of a gene can be made within a few hours
Does not require living cells
What does Semi-conservative ensure
Accuracy as complementary base pairing using the original strand as a template minimizes errors
Efficiency as replicating only half the molecule is faster than creating an entirely new DNA molecule from scratch
DNA Replication being Semi-conservative
DNA replication is semi-conservative as both DNA molecules produced are formed from an old and a new strand which are complementary to template strands
DNA Proofreading
DNA Polymerase III can check their work with each base that they add
DNA Polymerase III recognizes mismatched bases and removes and replaces the correctly matched with the nucleotides right away
DNA Polymerase III contains exonuclease that cleaves the phosphodiester bond between mismatched nucleotide
DNA proofreading prevents mutations, development of genetic diseases. cancer, and cellular disfunction
Leading and Lagging Strand in Replication
In the leading strand, the DNA Polymerase III moves towards the replication fork
In the lagging strand, the DNA Polymerase III moves away from the replication fork and synthesizes discontinuously in pieces called Okazaki Fragments. The lagging strand continuously needs new primers for the synthesis of each Okazaki Fragment
Role of Enzymes in DNA Replication
Gyrase decreases helical strain just ahead of Helicase
Helicase unwinds the DNA double helix by breaking the hydrogen bonds between the bases, separating it into two strands
Primase is an RNA polymerase which adds RNA primer at the 3’ end of each template strand to act as the starting point of replication
DNA Polymerase III binds to the primer and moves in opposite direction (5’ to 3’) and adds free nucleotides to each strand using complementary base pairing
DNA Polymerase I removes the RNA primers and replaces them with DNA
Ligase seals up the Okazaki Fragments together after Primers are removed to form a continuous strand
Why Does DNA Need to be Replicated?
Replication ensures that daughter cells inherit the same genetic information as the parent cell ensuring the continuity of genetic information, which leads to accurate passing of information across generations
