Who are these two famous characters of science?. Mendel (1865): Inheritance

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