BSC 1010 Chapter Notes - Chapter 14: Dna Polymerase Iii Holoenzyme, Dna Polymerase I, Erwin Chargaff

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8 Feb 2017

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Chapter 14: DNA: The Genetic Material
Transformation: The uptake of DNA directly from the environment; a natural process in some bacterial species
Experimented with and discovered by Fredrick Griffith
Avery, MacLeod, and McCarty identified DNA as the cause of transformation in Griffith’s experiments
Hershey and Chase experimented with viruses that infect bacteria (bacteriophages or phages)
used to differentiate the roles of DNA and protein
Friedrich Miescher discovered nucleic acid
Erwin Chargaff showed that the nucleotide composition of DNA molecules
Watson and Crick made the first models on DNA based on Rosalind Franklin’s images
Phosphodiester bond: The uptake of DNA directly from the environment; a natural process in some bacterial species
Two strands of the double helix are made up of long polymers of nucleotides, with each strand is made up of repeating sugar and
phosphate units joined by phosphodiester bonds (called the phosphodiester backbone)
Base-pairs: The uptake of DNA directly from the environment; a natural process in some bacterial species
Pattern of base-pairing is complementary
Adenine goes with thymine has a weak hydrogen bond so replication starts here
Guanine goes with cytosine
Structure is also antiparallel
has one strand going 5’ to 3’ and the other going 3’ to 5’
Meselson and Stahl determined that DNA replicates itself in semiconservative model
Is DNA replication in which each strand of the original duplex serves as the template for construction of a totally new
complementary strand, so the original duplex is partially conserved in each of the two new DNA molecules
DNA replication has a beginning (initiation), a middle (elongation), and end (termination)
DNA polymerase is the enzyme that actually matches the existing DNA bases with complementary nucleotides and the links them
together to make the new strand
Add new bases to the 3’ end of existing strands, going in a 5’ to 3’ direction
All DNA polymerases also require a primer to begin synthesis
o RNA polymerases usually synthesize the primers
DNA primase is a RNA polymerase that synthesizes short stretches of RNA hat function as primers for DNA
DNA polymerase I (DNA Pol I) acts on the lagging strand to remove priers and replace them with DNA
DNA polymerase II (DNA Pol II) is involved in DNA repair
DNA polymerase III (DNA Pol III) is the main replication enzyme and is responsible for the bulk of DNA synthesis
Helicases are enzymes that use energy from ATP to unwind the DNA template
single strands produced are unstable because they are exposed to hydrophobic bases to water
o exposed strands are coated with single-strand binding protein (SSB)
supercoiling refers to the coiling in space of double-stranded DNA molecules due to torsional strain, such as occurs when
the helix is unwound
o topoisomerases are enzymes used to relieve the torsional strain, specifically DNA gyrase
Ozazaki fragments are the DNA fragments synthesized on the lagging strand
Replication fork is the partial opening of DNA helix to form two single strands
All enzyme activity is here
leading strand is the strand that is continuous during synthesis
requires a single priming event
is extended indefinitely by the action of DNA Pol III
lagging strand refers to the strand that is discontinuous during synthesis
Ozazaki fragment are synthesized by DNA Pol III
primase is needed to synthesize primers for each Ozazaki fragment
removal and replacement of these is done by DNA Pol I
DNA ligase seals the “nicks” of the last phosphodiester bonds, joining the Ozazaki fragments to make a complete strand
Prokaryotic replication begins the origin and ends at the terminus
After initiation, replication proceeds bidirectionally from origin
Replicon is the origin of DNA replication and the DNA whose replication is controlled by this origin. In prokaryotic replication,
the chromosome plus the origin consist of a single replicon; eukaryotic chromosomes consist of multiple replicons
Nucleases are classified as either endonucleases (cut DNA internally) or exonucleases (chew away at the end of DNA)
Enzymes involved in DNA replication form a macromolecule assembly called replisome
Has two main subcomponents:
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