DNA Replication I Flashcards
When does DNA replication occur?
When chromosomes are duplicated prior to cell division
What happens to a single DNA molecule during DNA replication?
It is duplicated to create two new DNA molecules
Is there a difference in the replicated DNA molecule and the original DNA molecule?
No.
The new DNA molecules are identical in base sequence to one another and to the original DNA molecule.
What does a DNA molecule consist of?
Two strands with complementary base sequences
What does semiconservative mean in replication?
It means the two strands are separated and the base sequence of each strand is used to create a new strand with a complementary sequence
Whenthe two DNA molecules are created, what does each DNA molecule contain?
Each consists of one of the original strands and a newly synthesized complementary strand
What does the term semiconservative mean overall?
It reflects the fact that one original strand is conserved in each new DNA molecule, but that the second strand is new
What are the base sequences of the original strands used for in replication?
They are used to create new complementary strands
What is the original strand called in replication?
Template strand
Parental strand
What are the new strands called during replication?
Daughter strands
At the end of replication, what does the replicated DNA molecule contain?
There are two DNA molecules, each containing one template and one daughter strand
What is the shape of DNA in E. coli?
Circular
What kind of orientation does DNA have in E. Coli?
Antiparallel orientation
What is the first step in DNA replication?
To create an area within the DNA molecule where the two template strands are separated
Where does strand separation begin?
At a specific site within the DNA molecule called the origin of replication (ori)
What is oriC?
The ori in coli
What does oriC contain?
Specific base sequences that are important for the initiation of replication
What are the three types of base sequences in oriC?
A—T rush region
DnaA boxes
GATC methylation sites
When does initiation start?
When DnaA proteins bind to DnaA boxes within oriC
What happens when DnaA proteins are bound to DnaA boxes?
DnaA protein interact with one another to form a complex
How many H bonds are in A—T? What does that mean?
There are two H bonds in between adenine and thymine.
This means it is easier to break the base pairs when compared to G—C, which have three H bonds
What do the GATC methylation sites do?
They prevent premature initiation of a second round of DNA replication
What happens once the two DNA strands are separated at the AT rich regions?
DnaA proteins recruit DNA helicases to the separated regions
How many DNA helicase proteins are on each template strand?
Each template strand is bound by one DNA helicase
What direction does DNA helicase move?
5’ to 3’ direction
What does DNA helicase do as it moves down the template strand?
It breaks the H bonds that hold the template strands together, separating the strands, and uncoiling the DNA helix
Do the DNA helicase proteins move in the same direction at the same time?
No, they move in opposite direction away from the ori. This is because DNA strands are antiparallel
What do single-strand binding proteins prevent template strands from doing?
They attach to the separated template strands to prevent them from coming back together and reforming those bonds between bases.
This is because the bases within the two template strands have a natural tendency to reform H bonds.
What does the separation of the template strands allow for?
It allows for daughter strand synthesis to begin
What is a replication fork?
An area where the template strands are separated and where daughter strand synthesis is occurring
Why are there always two replication forks?
This is because separation and unwinding of the template strands occurs bidirectionally
What happens to the position of replication forks over time?
The positions will change, continuously moving farther and farther away from oriC
