AP BIOLOGY

Detailed explanation-1: -Primase synthesizes an RNA primer to initiate synthesis by DNA polymerase, which can add nucleotides only in the 5’ to 3’ direction. One strand is synthesized continuously in the direction of the replication fork; this is called the leading strand.

Detailed explanation-2: -One of the key molecules in DNA replication is the enzyme DNA polymerase. DNA polymerases are responsible for synthesizing DNA: they add nucleotides one by one to the growing DNA chain, incorporating only those that are complementary to the template.

Detailed explanation-3: -DNA primases are enzymes whose continual activity is required at the DNA replication fork. They catalyze the synthesis of short RNA molecules used as primers for DNA polymerases. Primers are synthesized from ribonucleoside triphosphates and are four to fifteen nucleotides long.

Detailed explanation-4: -Primase is the ssDNA-dependent RNA polymerase that synthesizes RNA primers during DNA replication. In common with all DNA and RNA polymerases, primase has structural and functional features involved in polymer elongation. As RNA polymerase, it has structural and functional features for initiating chain synthesis.

Detailed explanation-5: -Topoisomerases play critical roles in DNA replication, transcription, and chromosome structure by altering the topological state of DNA, . These enzymes are capable of relaxing supercoiled DNA and of decatenating interlocked DNA (Fig. 3.3. 1).