Chapter 14 Flashcards
Frederick Griffith
Studied streptococcus pneumoniae in rats
S virulent - causes disease. Polysaccharide coating
R - non virulent does not cause damage. No coating
Heat killed S and living R killed mouse through Transformation
Avery, Macleod and McCarthy
Repeated Griffith’s experiment by removing protein, RNA, and DNA to see what R cells received coating. DNA supported as genetic material
Hershey and Chase
Bacteriophages composed of only DNA and Protein. Used radioactive phosphorus in DNA and radioactive sulfur in protein. Protein became supernatant (liquid). DNA pellet in centrifuge spin. DNA is genetic material
DNA composed of
Nucleic acid composed of 5-carbon sugar (deoxyribose) phosphate group, Nitrogenous base (A,T,C,G) attached to 5-carbon sugar, free hydroxyl group attached at 3- carbon sugar
Purines and Pyrimidines
Purines - Adenine, Guanine. Double Ring
Pyrimidines - Cytosine, Thymine (DNA), Uracil (RNA). Single ring
Bonds between nucleotides or helix
Nucleotide Phosphodiester
Helix Hydrogen bonds
Antiparallel 5’ to 3’ and the other 3’ to 5’
Erwin Chargaff
Chargaff’s rule
Adenine = Thymine
Cytosine = Guanine
Always equal proportion of purines and pyrimidines
Rosalind Franklin
Performed x-ray diffraction. Discovered DNA as double helix (helical).
Diameter of 2 nm and makes a complete turn every 3.4 nm
James Watson and Francis Crick
Deduced with others work the structure of DNA as double helix with two polynucleotide chains running in opposite directions with hydrogen bonds between nitrogenous base.
Number of H bonds
A and T have 2 H bonds
C and G have 3 H bonds
Conservative model
Semiconservative model
Dispersive model
Conservative - Old with old strand. New strands together, two separate strands.
Semiconservative - Each double helix created gets one new strand and one old strand
Dispersive - Old and new strands mix parts, no fully new or fully old strands
Meselson and Stahl
Bacteria grown in heavy isotope of nitrogen N15 and then put in N14. Supported semiconservative model, rejected other 2
DNA Replication 3 steps
Initiation - replication begins
Elongation - new strands of DNA synthesized by DNA polymerase
Termination - replication is terminated
Zipping up coat
DNA polymerase
Matches existing DNA bases with complementary nucleotides and links them. Add new bases to 3’ end of existing strands. Synthesizes in 5’ to 3’ direction
RNA primer
Small sequence of RNA required to start replication
DNA primase makes RNA polymerase that makes RNA primer
Replicon
DNA controlled by an origin
DNA Polymerase 1 (pol 1)
Acts on lagging strand to remove RNA primers and replace with DNA
Has 5’ to 3’ exonuclease activity
Has 3’ to 5’ exonuclease activity (Proof reading)
DNA polymerase II (pol II)
Involved in DNA repair processes
Has 3’ to 5’ exonuclease activity (Proof reading)
DNA polymerase III (pol III)
Main replication enzyme.
Has 3’ to 5’ exonuclease activity (Proof reading)
DNA helicases
uses ATP energy to unwind DNA and break H bonds for replication
Single-strand-binding proteins (SBBs)
Coat strand to keep apart
Wedge strands apart, otherwise strands would go back together
Topoisomerase (DNA gyrase)
Prevent supercoiling due to pressure. Binds and relieves torsion strain ahead of replication fork
Lagging vs Leading strand
DNA polymerase can synthesize in only 1 direction
Leading strand synthesized continuously from initial RNA primer.
Lagging strand synthesized discontinuously with multiple RNA primers causing Okazaki fragments
Replication fork
Partial opening of DNA strands as replication occurs
Processivity
Beta subunit forms a sliding clamp to keep DNA pol III attached
DNA ligase
Seals backbone. Gaps between Okazaki fragments on lagging strand.
DNA Gyrase (Topoisomerase II)
unlinks 2 copies of DNA at termination site
Telomeres
Specialized structures found on ends of eukaryotic chromosomes. Protects ends of chromosomes from nucleases (degrade DNA) and maintain integrity of linear chromosomes. Gradual shortening of chromosomes with each round of cell division
Telomerase
Enzyme makes telomere section of lagging strand using an internal RNA template
Cancer cells generally show activation of telomerase
DNA Repair
Specific - Targets a single kind of lesion in DNA and repairs only that damage
Nonspecific - Use a single mechanism to repair multiple kinds of lesions in DNA
Mutagens
Any agent that increases the number of mutations above background levels (Radiation, chem, UV)
Photorepair
Specific repair mechanism for UV light
Thymine dimers get to close and have extra bonds of T to T
Photolyase cleaves thymine dimer and absorbs light in visible range
Excision Repair
Nonspecific. Damaged region removed and replaced by DNA synthesis
1 Recognition of damage
2 Removal of damaged region
3 Resynthesize using the information on undamaged strand as template
