DNA Replication Flashcards
Unit 3 Lesson 1 (14 cards)
What does it mean to run ‘5 to 3’ or 3’ to 5’
DNA strands run in opposite directions.
Each DNA strand has a 5’ (phosphate end) and a 3’ (OH end).
Unwinding the Helix is the first step to DNA Replication. What does this mean?
Topoisomerase relieves tension from the unwinding DNA coil
Helicase breaks the hydrogen bonds between base pairs, unzipping the DNA like a zipper.
(Replication fork)
Stabilizing the Open Strands is the second step to DNA Replication. What does this mean?
Single-Stranded Binding Proteins (SSBPs): Stick to the now-open strands to keep them from rejoining.
Starting the New Strand is the third step to DNA Replication. What does this mean?
Primase places a short RNA primer on each template strand (Primase creates RNA Primer) . This gives DNA polymerase a starting point to build the new complementary strands.
Is primase only used on the lagging strand?
No. It’s used on both strands, but more on the lagging strand because each Okazaki fragment needs a new RNA primer.
Building the New DNA is the fourth step to DNA Replication. What does this mean?
DNA Polymerase: Adds new DNA nucleotides
(A,T,C,G) to the primer, building in the 5’ to 3’ direction.
Leading vs. Lagging Strand is the fifth step to DNA Replication. What does this mean?
Leading strand is built continuously toward the fork. (<-)
Lagging strand is built in pieces (Okazaki fragments) away from the fork (->) since DNA polymerase only works 5’ to 3’.
Replacing Primers & Sealing Gaps is the sixth step to DNA Replication. What does this mean?
DNA polymerase removes RNA primers and replaces them with DNA.
DNA Ligase glues the Okazaki fragments together into one smooth strand.
Proofreading is the final step to DNA Replication. What does this mean?
DNA polymerase checks for errors and corrects any wrong base pairs.
How is DNA polymerase like a train during DNA replication?
DNA polymerase is like a train that moves along the DNA template from 5′ to 3′, dropping off DNA nucleotides (passengers) to build the new strand. On the leading strand, it moves smoothly; on the lagging strand, it stops and starts at each RNA primer (like shuttle trips)..
Why does DNA polymerase make shuttle trips on the lagging strand?
Because new track (RNA primers) keeps getting laid down by primase, so DNA polymerase can only build short sections at a time—like a shuttle train restarting at each new station (Okazaki fragment).
Why is DNA replication continuous on the leading strand but not on the lagging strand?
DNA polymerase can only build in the 5′ to 3′ direction. On the leading strand, this matches the direction of the fork, so it builds continuously. On the lagging strand, it runs opposite to the fork, it happens in short, discontinuous fragments.
Why is DNA replication called semi-conservative?
Because each new DNA molecule keeps one original strand and one newly made strand, conserving half of the original DNA in each copy.
What is a replication bubble and why is it important in humans?
A replication bubble is an open section of DNA where replication begins, with forks moving in opposite directions. Multiple bubbles form in the human genome to allow fast and efficient replication of its billions of base pairs.
