Question

a specialized enzyme called dna ligase, or just ligase, then catalyzes formation of a phosphodiester bond that closes the gap, creating a continuous sequence.
you may have noticed that as time goes on, the rna primer is gone and dna is now in its place. this makes sense; chromosomes are made of dna, not rna!
in case you were wondering, a specialized version of dna polymerase comes in after the main dna polymerase enzyme synthesizes the leading strand and each lagging strand fragment. this specialized dna polymerase removes the rna primer and replaces it with deoxyribonucleotides. in bacteria, this specialized enzyme is called dna polymerase i or just pol i; the main enzyme is dna polymerase iii or pol iii. there are many other enzymes in the dna polymerase \family\ of enzymes, including a pol ii.
which statements accurately compare leading and lagging strand synthesis? select all that apply.
□ lagging strand synthesis requires primase; leading strand synthesis does not.
□ lagging strand synthesis moves away from the fork; leading strand synthesis moves into the fork.
□ new deoxyribonucleotides are added to the 3 end during synthesis of the leading strand and the 5 end during synthesis of the lagging strand.
□ the leading and lagging strands are synthesized by the same individual dna polymerase molecule; this enzyme can work in two directions at once.
□ lagging strand synthesis occurs in fragments that have to be joined by ligase; leading strand synthesis is continuous from the point of origin.

Explanation:

• For the first option: Both leading and lagging strand synthesis require primase to synthesize RNA primers. So this option is incorrect.
• For the second option: The leading strand is synthesized continuously in the \(5'\to3'\) direction into the replication fork, while the lagging strand is synthesized discontinuously as Okazaki fragments moving away from the fork. This option is correct.
• For the third option: New deoxyribonucleotides are added to the \(3'\) end of both the leading and lagging strands (since DNA synthesis occurs in the \(5'\to3'\) direction for both strands). So this option is incorrect.
• For the fourth option: The leading and lagging strands are synthesized by different DNA polymerase molecules (e.g., in bacteria, pol III for leading and pol I for lagging - related functions in some aspects). Also, DNA polymerase works in the \(5'\to3'\) direction. So this option is incorrect.
• For the fifth option: The lagging strand is synthesized as Okazaki fragments that are joined by DNA ligase, while the leading strand is synthesized continuously from the origin. This option is correct.

Answer:

B. Lagging strand synthesis moves away from the fork; leading strand synthesis moves into the fork.
E. Lagging strand synthesis occurs in fragments that have to be joined by ligase; leading strand synthesis is continuous from the point of origin.