10.4-10.5: DNA Replication Flashcards
(15 cards)
What is the semiconservative model?
A model of DNA replication proposed by Watson and Crick. Suggests that DNA splits down the line of the bases, and then has free nucleotide pairs attach on to the two separate sides to form two sets of daughter DNA.
What are the limits of the semiconservative model?
Simplifies a very complex process. To untwist the DNA from its helical state and split the DNA takes the work of many enzymes. So while the model is correct, it is an oversimplification.
End of 10.4 Question: How does complementary base pairing make possible the replication of DNA?
When the two strands of the double helix separate, free nucleotides can base-pair along each strand, leading the synthesis of new complementary strands.
Where does replication of a DNA molecule begin?
At the origin of replication.
What are “bubbles” in the context of molecular DNA replication?
Bubbles are locations at the origins of replication in a DNA stand that are pulled apart by proteins and allow complementary bases to attach to the emerging daughter strands.
How many “bubbles” can be present at once? How does this affect DNA replication?
100s-1000s. This speeds up DNA replication because more bubbles means more space for complementary bases to attach and the parent DNA strands to fully separate.
What are primes? How do they factor into the structure of DNA?
Primes is the number of carbon atoms in each nucleotide sugar. There are two options: 5 prime (5’) and three prime (3’). The strands most be going in the opposite direction. When a phosphate group is found on the end, it is a 5’ end, and when it is the sugar, it is a 3’. Note that the sugar, 3’, end, attaches to a –OH group.
What enzyme is responsible for linking complementary nucleotides to parental DNA strands during DNA replication?
DNA polymerase.
What rules does DNA polymerase follow?
They only add nucleotides to the 3’ end of a strand and never the 5’. Daughter DNA strands only grow in the 3’–> 5’ direction.
Where does DNA polymerase work, in the context of bubbles?
A forking point in a bubble.
What are the short-pieces, or bubbles, called in DNA replication? What makes separates them from being an independent daughter strand?
Okazaki fragments. They have complementary base pairs, however the entire strand is not linked together yet.
What is the responsibility of DNA ligase?
To link the Okazaki fragments together and complete a strand of DNA.
Besides their functions in DNA replication, what doess DNA polymerase and ligase also do?
Polymerase do a “proof-reading” to guarantee no bases have been paired incorrectly. Both work in repairing cells damged by radiation such as UV, x-rays and toxic chemicals found in cigarette smoke.
End of 10.5 Question: What is the function of DNA polymerase in DNA replication?
As free nucleotides base-pair to a parental DNA strand, the enzyme covalently bonds them to the 3’ end of a growing daughter strands.
Note:
I don’t think I understand the function of ligase.
