Class notes Nursing (Biochemistry)

NUCLEIC ACIDS SYNTHESIS

, DNA REPLICATION
• Basic Concept = create a new strand by matching nucleotides to an existing strand
• Replication is semi-conservative (one strand is old, one strand new)




General Process of DNA Replication
• Step 1: Initiator Proteins bind to origins of replication to begin replication
Attracts other enzymes involved in replication process
• Step 2: DNA Helicase separates the DNA helix
• Step 3: Primase builds an RNA primer at the starting from the 5’ end of the new DN
Uses the 3’ end of existing DNA strand

, Primase



3’ 5’

5’


RNA Primer




DNA Polymerase III
Step 4: DNA Polymerase builds the new strand of DNA in a 5’ to 3’ direction by adding
nucleotides

, • How can both strands of DNA be replicated in a 5’- 3’ direction at the same tim
antiparallel?
• Answer: leading and lagging strands
Leading and Lagging Strands
Leading strand is synthesized continuously in the direction of replication (goes in
direction as helicase)
Lagging strand is synthesized in short fragments in the opposite direction of replicatio
direction as helicase)
DNA Ligase seals DNA fragments together