10
1. Before a cell divides, it must replicate its DNA. This ensures each resulting daughter cell has a full copy of chromosomes.
2. The double helical structure of DNA is antiparallel. This means that the 3′ end of one strand (which has a hydroxyl/–OH group hanging off of it) must line up with the 5′ end of the complementary strand (which has a phosphate group hanging off of it).
3. The lagging strand needs multiple RNA primers.
4. Free nucleotides are added to a growing strand of DNA through a dehydration reaction, which creates a new phosphodiester bond.
5. In order for DNA polymerase to attach a nucleotide through a dehydration reaction, there needs to be a free –OH (hydroxyl) group available; the 3′ end of a DNA molecule has a free hydroxyl group.
6.
a. The enzyme helicase unwinds and unzips DNA in order for replication to occur.
b. The enzyme primase must first synthesize a small piece of RNA in order for another enzyme to begin adding DNA nucleotides to the growing strand.
c. Once DNA is unzipped, single-stranded binding proteins stick to the unpaired bases in order to keep the two strands apart.
d. The enzyme ligase glues together fragments of newly synthesized DNA by creating new phosphodiester bonds.
e. The bulk of the work of creating a new strand of DNA is done by DNA polymerase, the enzyme responsible for pairing up complementary nucleotides.
7. First, in order for DNA polymerase to be able to create two identical DNA molecules, the original DNA must be double stranded. Otherwise, if the original DNA was a single strand, the newly synthesized strand would be a complementary (not identical) copy. Second, double-stranded DNA is much more stable than a single-stranded piece.
8. b. One strand from the original DNA molecule and one created from new nucleotides
9. False. Immediately after the DNA replication (and before the cell splits into two daughter cells), another DNA polymerase will replace the RNA primers with DNA.
10. a. When DNA is replicated, it is crucial that the resulting daughter cells have exactly the same compliment of DNA as the parent cell.