Question

what is the role of single-strand binding proteins during dna replication?
○ a. unwinds the double helix
○ b. synthesizes rna primers
○ c. stabilizes the unwound dna strands
○ d. seals gaps between okazaki fragments

what characterizes the lagging strand during dna replication?
○ a. it does not require okazaki fragments
○ b. it is synthesized in the 5’ to 3’ direction only
○ c. it is synthesized in short, discontinuous fragments
○ d. it is synthesized continuously

what is the direction of synthesis of the leading strand during dna replication?
○ a. 3’ to 5’
○ b. 5’ to 5’
○ c. 5’ to 3’
○ d. 3’ to 3’

Explanation:

First Question: Role of single - strand binding proteins

• Option a: Helicase unwinds the double helix, not single - strand binding proteins.
• Option b: Primase synthesizes RNA primers.
• Option c: Single - strand binding proteins bind to the unwound single - stranded DNA and stabilize it, preventing it from re - annealing.
• Option d: DNA ligase seals gaps between Okazaki fragments.

• Option a: The lagging strand is synthesized as Okazaki fragments, so it does require them.
• Option b: Both leading and lagging strands are synthesized in the 5' to 3' direction.
• Option c: The lagging strand is synthesized in short, discontinuous fragments (Okazaki fragments) because DNA polymerase can only add nucleotides in the 5' to 3' direction and the template for the lagging strand is oriented in the 5' to 3' direction away from the replication fork.
• Option d: The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously.

• DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand. So, during DNA replication, both the leading and lagging strands are synthesized in the 5' to 3' direction. The leading strand is synthesized continuously in this direction as the replication fork moves.
• Option a: DNA is not synthesized in the 3' to 5' direction by DNA polymerase during replication.
• Option b: 5' to 5' is not a valid direction for DNA synthesis.
• Option d: 3' to 3' is not a valid direction for DNA synthesis.

Answer:

c. Stabilizes the unwound DNA strands

Second Question: Characteristics of the lagging strand