Not Important Flashcards
When does DNA replication occur?
During cell division
What specific phase of cell division does DNA replication occur?
S-Phase of the Cell Cycle
What must DNA replication be?
Accurate
What does DNA replication involve?
Copying one DNA molecule into two identical molecules
When discovered, DNA structure suggested what?
How DNA was able to replicate
Step 1 of how DNA was able to replicate
The H-bonds between complementary bases break;
This allows the DNA to unzip
Step 2 of how DNA was able to replicate and what does this result in?
- Each DNA strand then acts as a template to build the complimentary strand
- This results in two identical DNA molecules; one for each daughter cell
What were the three methods of DNA replication in question?
-Conservative Method
-Semi-Conservative Method
-Dispersive Method
What does the Conservative Method involve?
The original double-stranded DNA being conserved as one molecule for one daughter, and a completely new one for the other daughter,
What does the Semi-Conservative method involve?
The original molecule is split in half, and the other side is filled-in)
What does the Dispersive method involve?
Each new molecule is comprised of bits and pieces of both new DNA and the original strand
What did scientists Meselson and Stahl’s experiment involve?
Growing Escherichia coli (E. coli.) in 15N media, which made the DNA heavy.
What did Meselson and Stahl then do?
Then grew it on normal media (14N).
What were the 2 possible outcomes of Meselson and Stahl’s experiment?
1)New molecules have medium (hybrid) DNA or
2) One molecule has heavy DNA the other light,
What outcome was ultimately observed?
The first was observed
Although DNA replication has many steps, what are the general steps?
Initiation and unzipping.
Priming
Elongation
Proof-reading.
What are the key steps in DNA replication?
DNA polymerase III
DNA polymerase I
Leading strand
Lagging strand
Okazaki fragments
RNA primase
Helicase
Gyrase
Ligase
Initiation and Unzipping: When does Replication begin?
When proteins bind at a specific site on the DNA known as the origin of replication (ori).
Differences and similarities between eukaryotic replication and prokaryotic replication
Eukaryotic replication is similar to prokaryotic replication but more complex
How many origins of replication does the closer circular DNA of prokaryotes have?
They usually have only one.
How many origins of replication does linear eukaryotic DNA have?
Have multiple
DNA Strand Separation: Why can’t DNA strands be pulled apart?
because they are held together by hydrogen bonds and twisted around each other in the double helix.
How are DNA template strands exposed?
When specific enzymes work together
What is involved in DNA strand separation?
DNA helicase, which unwinds the double helix by breaking the H-bonds at the replication fork
DNA Strand Separation: What is a Replication Fork?
Region where enzymes replicating
DNA bind to an untwisted, s.s. DNA strand
DNA Strand Separation: What are Single-stranded Binding Proteins (SSBs)?
bind the exposed DNA template strands to block new H-bonds that would re-join the strands
DNA Strand Separation: What is DNA Gyrase?
- relieves tension from the unwinding of the DNA strands.
- It cuts nicks in both strands of DNA, allowing them to swivel around one another and then resealing the cut strands
DNA Replication: How does replication begin?
in 2 directions from the ori ’s as a region of the DNA is unwound.
DNA Replication: How does it proceed?
toward the direction of the replication fork (leading strand) on one strand and away from the fork (lagging strand) on the other strand.
DNA Replication: In eukaryotes, what happens if 2 replication forks are too near?
a replication bubble forms
Priming for Elongation: DNA polymerase cannot do what?
start incorporating nucleotides on its own
Priming for Elongation: DNA polymerase needs what?
an existing 3’ end of a nucleic acid
Priming for Elongation: What provides that end?
A short segment of RNA (a “primer” - 10 to 60 nucleotides long)
Priming for Elongation: What does RNA primase do?
synthesizes the primer and anneals it to the template strand
Priming for Elongation: After RNA Primase is added, what can DNA polymerase then do?
add on DNA nucleotides
