1.
a. Helicase - Unwinds the DNA double helix by breaking hydrogen bonds between base pairs.
b. Single-strand binding proteins (SSBs) - Stabilize single-stranded DNA and prevent reannealing.
c. Primase - Synthesizes short RNA primers to provide a 3’ OH group for DNA polymerase to begin synthesis.
d. DNA polymerase III - Main replicative enzyme that synthesizes new DNA strands in the 5’ to 3’ direction.
e. DNA polymerase I - Removes RNA primers and replaces them with DNA nucleotides.
f. DNA ligase - Joins Okazaki fragments on the lagging strand by catalyzing phosphodiester bonds.
g. Topoisomerase (or gyrase) - Relieves torsional stress ahead of the replication fork by cutting and rejoining DNA strands.
2.
- Leading strand: The strand synthesized continuously in the 5’ to 3’ direction toward the replication fork.
- Lagging strand: The strand synthesized discontinuously away from the replication fork as short segments (Okazaki fragments).
They are made differently because DNA polymerase can only add nucleotides in the 5’ to 3’ direction, and the two template strands are antiparallel. As the fork opens, one strand (leading) allows continuous synthesis, while the other (lagging) requires repeated primer synthesis and fragment joining.
3.
Primase, DNA polymerase III, DNA polymerase I, and DNA ligase are mainly involved in the production of the lagging strand.
Parent Tip: Review the logic above to help your child master the concept of dna replication worksheet.
