DNA Replication Flashcards
Griffith Experiment
(Explain experiment design and its conclusion)
2 strains of bacteria:
R-strain=Non-viral
S-Strain= Viral (pathogenic) ; Kills host
Live S: dead mouse
Live R: healthy mouse
Heat-killed S: healthy mouse
Heat-killed S + Live R: dead mouse
Conclusion: R cells “transformed” by genetic material of S cells
-> Griffith discovers transformation
Hershey-Chase Experiment
radioactive sulfur and phosphorus to trace protein and DNA in order to determine which macromolecule enters the bacterial cells/ carries genetic material
-Sulfur labels protein
-Phosphorus labels DNA
Experiment found phage protein found in liquid and phage DNA was found in the pellet
-> genetic information stored in DNA not proteins
Clicker:
If we conducted the Hershey-Chase experiment again using radioactive
15N, where would you expect to find the radioactive signal (and what
part of the macromolecule is being labelled?
A. Within the bacterial pellet, inside the bacteria
B. In the supernatant outside of the bacteria
C. In neither the bacterial pellet or the supernatant as the phage do not comprise of any macromolecule that uses N
D A and B
E. Not enough information is given.
d.) A and B
backbone of every nucleotide contains at least 2-3 nitrogen per each nitrogenous base.
-> Therefore the radioactive element would be present everywhere
Messelson-Stahl Experiments
proved semi-conservative model of DNA replication.
Clicker:
In Meselson and Stahl’s experiment studying DNA replication, they started
with bacteria grown in a heavy isotope of nitrogen and then switched them
to a light isotope. They then observed the DNA density after one and two
rounds of replication. What was the result after one round of replication?
A. Equal amounts of light and hybrid DNA
B. All hybrid DNA
C. Equal amounts of light, hybrid, and heavy DNA
D. Twice as much light as hybrid DNA
E. Three times as much light as hybrid DNA
B.) All hybrid DNA
Clicker:
In Meselson and Stahl’s experiment studying DNA replication, they started
with bacteria grown in a heavy isotope of nitrogen and then switched them
to a light isotope. They then observed the DNA density after one and two
rounds of replication. What was the result after two rounds of replication?
A. Equal amounts of light and hybrid DNA
B. All hybrid DNA
C. Equal amounts of light, hybrid, and heavy DNA
D. Twice as much light as hybrid DNA
E. Three times as much light as hybrid DNA
a.) Equal amounts of light and hybrid DNA
Clicker:
In Meselson and Stahl’s experiment studying DNA replication, they started
with bacteria grown in a heavy isotope of nitrogen and then switched them
to a light isotope. They then observed the DNA density after one and two
rounds of replication. If they had tested their bacterial samples after three
rounds of replication, what would they have observed?
A. Equal amounts of light and hybrid DNA
B. All hybrid DNA
C. Equal amounts of light, hybrid, and heavy DNA
D. Twice as much light as hybrid DNA
E. Three times as much light as hybrid DNA
E.) Three times as much light as hybrid DNA
DNA Polymerases
Enzyme family responsible for catalyzing the formation of phosphodiester bonds between nucleotides.
-3’ to 5’
-Adds new nucleotide at 3’ end
-require primers
1,2,3 all build DNA
1.) Fixes mismatches and gaps
2.) Proofreads lagging strand of DNA synthesis
3.) main enzyme of DNA synthesis
Molecular components of DNA Replication? (4)
1.) DNA Helicase
2.) Topoisomerase
3.) DNA Polymerase lll
4.) Primase
DNA Helicase
Separates two strands of DNA
Topoisomerase
stabilizes helix during unwinding to prevent supercoiling
DNA Polymerase lll
Catalyzes formation of new phosphodiester bonds between nucleotides incorporated into the new strand.
Primase
Lays down template RNA primers for DNA pol lll to recognize and bind
Leading Strand
Synthesized in the same direction as the growing replication fork
-continuous synthesis
Lagging Strand
Discontinuous synthesis in the opposite direction of the growing replication fork.
*Okazaki Fragments -> Fused together by DNA ligase
