DNA Replication Flashcards
List and explain the proposed mechanisms for DNA replication.
- Conservative model - both strands of parental duplex remain intact
• New DNA copies consist of all new molecules
• No conservation from parental templates - Semiconservative model - each daughter duplex consist of one parental strand and one new strand
• Hybrid molecule of new and old strand - Dispersive model - new DNA is dispersed through each strand of both daughter duplexes after replication
Describe semi-conservative replication through first and second replication.
First replication: half and half
Second replication: half and half with one with new material
Describe dispersive replication through first and second replication.
First replication: new DNA dispersed within daughter strand
Old material keeps shrinking for each generation
Explain the methods of the Meselson and Stahl experiment
What were the results from Meselson and Stahl’s experiment?
DNA synthesis produced a __________ of the template strand
Reverse complement
Where does DNA synthesis begin?
Replication origins
Replication origin are A-T rich, meaning?
More As and Ts in this region
Easier to break hydrogen bonds
How many replication forks form at each replication origin?
2
DNA replication in both prokaryotes and eukaryotes is _________.
Bidirectional
Why is the rate of replication slower in eukaryotes?
No histones in bacteria (no heterochromatin)
Eukaryotes: levels of compaction that has to be dealt either (e.g., moving histones
What does DNA polymerase do?
Synthesizes DNA by adding nucleotides to 3’ end of growing chain
DNA (and RNA) is always synthesized in the _______ direction
5’-3’
Where does the energy for polymerization by DNA polymerase come from?
Hydrolysis of incoming dNTP
What is the by product of using hydrolysis of dNTP as energy?
Pyrophosphate
What kind of metabolic process is DNA synthesis? Anabolic or catabolic?
Anabolic
T or F: DNA replication is continuous
F: DNA replication is semidiscontinuous
What does DNA ligase do?
Join Okazaki fragments together
Short Okazaki fragments are formed on the _______
Lagging strand
Explain DNA polymerase’s proofreading mechanism
Contains 3’ to 5’ exonuclease activity (removes improperly added dNTP)
What is primase and what does it do?
• Type of RNA polymerase
• Puts down temporary RNA primers
T or F: DNA polymerase can initiate DNA synthesis without a primer
F: DNA polymerase cannot initiate DNA synthesis without a primer
What is the difference between the leasing and lagging strand when it comes to primers?
Leading strand: only requires one primer
Lagging strand: continuously requires new primers to generate new Okazaki fragments
What does DNA helicase do?
Pries apart double helix
What is the function of single strand binding proteins?
Prevent two strands (on lagging template) from rebinding back together
What is the function of the sliding clamp?
Holds DNA polymerase onto DNA strand
What is processivity? How does it relate to the sliding clamp and its loader?
Processivity - being able to stay engaged with DNA before it falls off
Sliding clamp has high processivity
No sliding clamp = DNA polymerase would fall off more often
T or F: Clamp loader requires ATP
True
What does semicontinuous replication mean? How does replication of the lagging strand differ from the leading strand? How is this coordinated?
What are the two ways that torsional strain resulting from DNA unwinding be relieved during replication? What enzyme is involved?
- DNA supercoiling - temporarily relieves tension
- DNA topoisomerase - relieves tension long term
• Two enzymatic activity: nuclease and ligase
- How does telomerase replicate the ends of eukaryotic chromosomes?
- Is telomerase required in non dividing cell? Why?
(1)
• Repetitive DNA sequences added to telomeres
• This is done using its own RNA template
- Yes
Bacteria don’t require telomerase. Why?
Chromosomes are circular (do not require telomeres)
Where does DNA replication occur in mitosis?
S phase
What is a replication fork?
Y-shaped junction at site where DNA is being replicated
What is meant by DNA replication being bidirectional?
Two replication forks move away from replication origin in opposite directions
What is DNA polymerase?
Enzyme that catalyzes addition of nucleotides to 3’ end of growing DNA strand
What is primase?
Enzyme that synthesizes RNA primers
What is the function of the sliding clamp?
Keep DNA polymerase firmly attached to template
What is the function of the clamp loader?
Lock sliding clamp around DNA
