1. DNA replication is semi-conservative, meaning each new DNA
molecule consists of one old strand and one new strand. How
does this method of replication help ensure genetic continuity?
What would be the implications if DNA replication were fully
conservative or fully dispersive?
DNA replication is semi-conservative, meaning each new DNA molecule
keeps one original strand and builds one new strand. This ensures genetic
continuity because the parental strand acts as a template that guides the
correct addition of complementary bases, following the A-T and G-C pairing
rule. This greatly reduces errors and helps preserve the DNA sequence
through generations. If replication were fully conservative, the entire original
double helix would stay intact, and a completely new molecule would be
made, which would remove the template checking advantage and lead to
more mistakes. If replication were fully dispersive, each strand would be a
mix of old and new DNA, making the molecule unstable and making accurate
proofreading very difficult.
2. The leading and lagging strands are synthesized differently
due to the directionality of DNA polymerase. How do the
differences in their synthesis highlight the constraints of DNA
polymerase? Why is this process so carefully regulated?
DNA polymerase can only build DNA in the 5′ to 3′ direction, which causes
the two strands to be made differently. The leading strand is synthesized
continuously, while the lagging strand is built in short Okazaki fragments
because it runs in the opposite direction of the replication fork. This shows
that DNA polymerase cannot work backward and cannot begin without a
primer. Because of these limitations, several enzymes, helicase, primase,
topoisomerase, and ligase work together to control replication. The process
is carefully regulated because accuracy is essential; mistakes can cause
mutations. Proofreading by DNA polymerase and mismatch repair helps keep
errors extremely rare.
molecule consists of one old strand and one new strand. How
does this method of replication help ensure genetic continuity?
What would be the implications if DNA replication were fully
conservative or fully dispersive?
DNA replication is semi-conservative, meaning each new DNA molecule
keeps one original strand and builds one new strand. This ensures genetic
continuity because the parental strand acts as a template that guides the
correct addition of complementary bases, following the A-T and G-C pairing
rule. This greatly reduces errors and helps preserve the DNA sequence
through generations. If replication were fully conservative, the entire original
double helix would stay intact, and a completely new molecule would be
made, which would remove the template checking advantage and lead to
more mistakes. If replication were fully dispersive, each strand would be a
mix of old and new DNA, making the molecule unstable and making accurate
proofreading very difficult.
2. The leading and lagging strands are synthesized differently
due to the directionality of DNA polymerase. How do the
differences in their synthesis highlight the constraints of DNA
polymerase? Why is this process so carefully regulated?
DNA polymerase can only build DNA in the 5′ to 3′ direction, which causes
the two strands to be made differently. The leading strand is synthesized
continuously, while the lagging strand is built in short Okazaki fragments
because it runs in the opposite direction of the replication fork. This shows
that DNA polymerase cannot work backward and cannot begin without a
primer. Because of these limitations, several enzymes, helicase, primase,
topoisomerase, and ligase work together to control replication. The process
is carefully regulated because accuracy is essential; mistakes can cause
mutations. Proofreading by DNA polymerase and mismatch repair helps keep
errors extremely rare.
