Lecture 11 Flashcards
3 properties of genetic material
1) carry info
2) replicate faithfully; transmit info
3) have variation
DNA was not thought to be hereditary info (up to ~70 yrs ago!) but instead ____ were.
Why?
Proteins
- b/c DNA has only 4 possible monomers (not a lot of combinations/ variation) but proteins have 20 possible monomers
Experiments (in order) discovering DNA
- Griffiths Transformation Experiment
- Avery, MacLeod, and McCarty Experiment
- Hershey and Chase Experiment
- Watson and Crick
- Meselson- Stahl
G AMM HC WC MS
transforming principle=
an abiotic factor that carries hereditary info
Griffith’s experiment
- question
- experimental design
- findings
- Is there a transforming principle?
- heat killed S strain mixed with live R-strain (neither killed the mouse separately) kills the mouse
- there’s an abiotic transforming principle (DNA or protein)
Avery, MacLeod, and McCarty Experiment
- question
- experimental design
- findings
-Q: what is the transforming principle?
- exp: repeated Griffith’s experiment and added enzymes to specifically degrade different macromolecules
If DNA is degraded, mouse lives
- Finding: DNA is the transforming principle
Hershey and Chase Experiment
- question
- experimental design
- findings
- Is DNA the universal transforming principle?
- exp: used phase and radioactivity to differentiate label proteins vs DNA
S35= proteins
P32= DNA
S35 labelled phage: radioactivity is in the supernatant, not the pellet
P32 labelled phage: viral DNA enters the bacterial cell, and the pellet is now radioactive
Conclusion: DNA is the universal transforming principle
Watson and Crick discovered:
(3 things)
by using the ____ rule and the x-ray crystallography images by _____ ___
- DNA is double helix
- sugar-phosphate backbone
- complementary base pairing (A to C and C to G)
- Chargaff’s rule
- Rosalind Franklin
What 3 forces stabilize DNA?
1) phosphodiester bonds= covalent bonds that form the backbone
2) H-bonds: base pairing
3) Hydrophobic base stacking
DNA replication happens in the __-phase of the cell cycle
S phase
List Meselson-Stahl’s 3 possible models for DNA replication
- Conservative
- Semi conservative
- Dispersive
describe the conservative DNA replication model
the entire parent is photocopied
describe the semi-conservative DNA replication model
each parent strand acts as a template for daughter strand synthesis
describe the dispersive DNA replication model
analogy: photocopy, throw pages in the air and hope they come down with one page in each version
- bad model- very inefficient
- each molecule is a random collection of parent/ daughter
How did Meselson-Stahl determine that semiconservative DNA replication was correct?
used radioactivity to change the molecular mass of nitrogen
all nucleic acids are polymerized by adding nucleotides to the __ end
3’
3’ OH
the enzyme of DNA replication is __ ______ which:
DNA polymerase
- catalyzes phosphodiester bond formation
substrate of DNA replication is ___
- the energy for replication comes from hydrolysis of __
dNTPs (where N is replaced with A, C, T, or G)
Pi
___ _____ gives specificity
base pairing
the leading strand is synthesized in the same direction as __ ___
fork opening
the lagging strand is synthesized in the ____ direction of fork opening
opposite
what happens in the initiation step in dna replication
- DNA helicase unwinds the double helix (at the origin or replication) after the initiation protein attracts it
- the single strands are now templates
- Primase synthesizes the RNA primer and DNA polymerase III will start adding nucleotides (5’ to 3’ direction)
- SSBs keep the bubble unwound by staying in the replication forks
what happens in the elongation step in dna replication
- complementary base pairing occurs and DNA polymerase III catalyzes the actual joining of the nucleotides
- they’re linked through phosphodiester bonds in a process called polymerization
- DNA pol I removes the primer and DNA ligase connects the spaces (fills in Okazaki fragments)
