DNA Replication Elongation
Catalyzes the elongation
Adds nucleotide (nucleoside triphosphate) to the growing end of new DNA strand
Adds only 5' to 3'
Rate of elongation:
Bacteria: 500 nucleotides per second
Humans: 50 nucleotides per second
How to get rid of RNA primer?
DNA Polymerase comes in to replace the RNA primer and DNA is made now besides a hybrid
Direction of Replication follows the leading strand/ follows the zipper
Lagging Strands Synthesis: Okazaski Fragments
Short segment of DNA synthesis away from the fork
DNA fragments joined by DNA ligase to form a single strand, fixes the nicks
Lagging strand require new primers as the replication fork progresses
Semiconservative DNA Replication
Mechanism of DNA Replication
Specific Enzymes and other proteins carry out DNA replication
E. Coli replicates its 5 million base pairs chromosomes and divide it into daughter cells in less than an hour
A human cell can copy its 6 billion base pairs and divide into daughter cell
Remarkably accuate: one error per billion nucelotides
Special sites where DNA replication begins, eukaryotes have hundreds of thousands of origin sites per chromosome
DNA Replication Initation
DNA polymerases cannot initiate synthesis of polynucleotides
only adds nuceotides to the end of an existing chains of nucleic acid
Protein players to inititte DNA synthesis
Primase: Enzyme that makes RNA called a primer, makes in 5' to 3' direction
Single Strand Binding Proteins: Keeps the complementary base pairing from joining back together.
Helicase: "Unzips" the double helix
Topoisomerase: Enzyme that prevents coiling by creating nicks to relax the DNA so it doesn't coil on itself
Why 5' to 3'
If it goes 3' to 5', the rings of the nucleotide will get in the way and wouldn't allow other bases to fit