The MOLECULAR Basis of Inheritance. n Structure & Function!!!
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Transcript of The MOLECULAR Basis of Inheritance. n Structure & Function!!!
The MOLECULAR Basis of Inheritance.
Structure &
Function!!!
Searching for Genetic Material, I Mendel: modes of heredity in pea plants Morgan: genes located on chromosomes Griffith: bacterial work; transformation: change in genotype
and phenotype due to assimilation of external substance (DNA) by a cell
Avery: transformation agent was DNA
Searching for Genetic Material, II
Hershey and Chase used bacteriophages (phages) to deduce that:
– √ DNA (not protein) is the hereditary material Experiment: sulfur(S) is in protein, phosphorus (P) in DNA;
only P was found in host cell
DNA Structure
Chargaffratio of nucleotide bases (A=T; C=G)
Watson & Crick (Wilkins, Franklin)
The Double Helix √ nucleotides: nitrogenous base (thymine, adenine, cytosine, guanine); sugar deoxyribose; phosphate group
DNA Bonding
Purines: ‘A’ & ‘G’ Pyrimidines: ‘C’ & ‘T’
(Chargaff rules) ‘A’ H+ bonds (2) with ‘T’ ‘C’ H+ bonds (3) with ‘G’ Van der Waals
attractions between the stacked pairs
DNA Structure
Campbell Animation
DNA Replication Watson & Crick strands are complementary; nucleotides line up on template
according to base pair rules (Watson)
Meselson & Stahl replication is semiconservative; Expt: varying densities of radioactive nitrogen
Meselsen/Stahl Animation
DNA Replication: 500 nucleotides/sec!! Begin at “Origins of replication”
– A specific sequence of nucleotides; 1000s per chromosome Replication forks open to form “replication bubbles”. 2 main stages: Separation & Synthesis Separation:
– Helicase:catalyzes the untwisting of the DNA at the replication fork– Single Strand Binding Proteins: hold the helix open
Synthesis:– DNA polymerase:catalyzes the elongation of new DNA
By the way, DNA has an…. Antiparallel nature: • sugar/phosphate
backbone runs in opposite directions
• one strand runs 5’ to 3’, while the other runs 3’ to 5’
• DNA polymerase only adds nucleotides at the free 3’ end, forming new DNA strands in the 5’ to 3’
direction only
Synthesis: Initiation: Primer (short RNA sequence
is attached first with “primase”) DNA Polymerase then attaches each
new nucleotide to the growing strand using “nucleoside triphosphate”
DNA Pol can only add 5’ to 3’ so… Leading strand: synthesis toward the
replication fork is “continuous (5’ to 3’ direction from the 3’ to 5’ master strand)
Lagging strand: synthesis away from the replication fork is discontinuous.
Okazaki fragments; joined by DNA ligase (must wait for 3’ end to open; again in a 5’ to 3’ direction)
DNA Replication
http://www.johnkyrk.com/DNAreplication.html
DNA Repair
Mismatch repair: DNA polymerase
Excision repair:Nuclease
Telomere ends:telomerase
More Animations!!!
http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/dna_replication.htm
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf
http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm
http://207.207.4.198/pub/flash/24/menu.swf