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Who are these two famous characters of science?
Mendel (1865): Inheritance
T.H. Morgan (1910): genes linked on chromosomes
Chromosomes are made of DNA and proteins
DNA and proteins are the two candidates for the genetic material
Griffith(1928): bacterial work- streptococcus pneumoniae
Transformation: change in genotype and phenotype due to assimilation of external substance (DNA) by a cell
Avery and team(MacLeod and McCarty)(1944): transformation agent was DNA
Hershey and Chase(1952): determine that DNA is the hereditary material and not proteins:
Watson & Crick(Wilkins, Franklin)(1953):The Double Helix
Basic Unit of Nucleic Acids = nucleotideSugar/ phosphate backboneNitrogen base
5 carbon sugar = ribosePhosphate group
Phosphodiester bond
In DNA there are four(make up the interior of the molecule):AdenineThymineCytosineGuanine
Two groups:Purines: double ringed structures
Adenine and GuaninePyrimidines: single ringed
structuresThymine and Cytosine
5’ to 3’5’ with the phosphate group3’ with the –OH group
Inward facing nitrogen base will pair with their complementary base
A will pair with T (two H- bonds)G will pair with G (three H- bonds)A double ringed structure will always pair with a single ringed structure to maintain width.
DNA strands are oriented in the opposite directions
Van der Waals attractions play a role in holding the DNA molecule together
Proposed the semiconservative model of DNA replication:
DNA polymeraseHelicasePrimaseDNA ligaseTopoisomerase
Sites where DNA replication beginsProkaryotes: one origin
Replication proceeds in two directions
Humans: hundreds maybe thousands of originsReplication proceeds in two directions
Replication bubble: unwinding and separation of the DNA strand
Replication fork: Y- shaped region at each end of the bubble
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Elongation catalyzed by DNA polymeraseE. coli bacteria adds nucleotides at
a rate of 500/secHumans add nucleotides at a rate
of 50/secNucleoside triphosphate:
Antiparallel elonagation:5’ – 3’ direction
Leading strandLagging strand
Okazaki fragmentsE. coli fragments: 1000- 2000 nucleotides Human fragments: 100 -200
Meselson & Stahl replication semiconservative;
Expt: varying densities of radioactive nitrogen
Briefly describe the role of the following enzymes involved in DNA replication: DNA polymerase IDNA polymerase IIIHelicaseDNA ligaseTopoisomerasePrimase
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How many primers are needed for the leading strand?
How many primers are needed for the lagging strand?
DNA replication ensures continuity of hereditary information:
1. Enzymes of DNA replication work as part of a large complex:
2. Replication process is probably a stationary processDNA polymerase “reels- in” the parent DNA
Lagging strand may may be looped
Pairing errors occur at the rate of 1 out of every 100, 000 base pairs
DNA polymerase proof reads each nucleotideIncorrectly paired nucleotides are immediately removed and replaced
Mismatch pair: Repaired by the action of nuclease(one of many different DNA repair enzymes)
Removes nucleotides damaged by chemicals or the environment
Telomeres= nucleotide sequences at the ends of the DNA moleculeContain a repeated unit TTAGGGDo not contain genesNo nucleotides addedProtects the molecule from the replication
processTriggers apoptosisMay contribute to the aging process
Catalyzes the lengthening of the telomeres in eukaryotic germ cells