DNA Replication

Initiation

First stage of DNA replication; DNA is unwound and strands are separated to begin copying

Elongation

Stage where DNA polymerase synthesizes new DNA strands by adding nucleotides 5' → 3'

Termination

Final stage where DNA ligase seals fragments and replication is completed

5' to 3' Synthesis

Direction DNA polymerase builds new DNA; nucleotides are always added to the 3' end

3' to 5' Template

Orientation the template strand must be read for proper DNA synthesis

DNA Topoisomerase

Relieves supercoiling and untwists dsDNA at the origin of replication

Helicase

Separates the DNA strands by breaking hydrogen bonds; moves 5' → 3'

Single-Strand Binding Proteins (SSBs)

Keep the separated DNA strands from re-annealing

Origin of Replication

Specific site where replication begins

DNA Polymerase

Adds nucleotides 5' → 3' and proofreads for mismatches

dNTP (Deoxynucleoside Triphosphate)

Incoming nucleotide used for elongation; provides energy when phosphate bonds break

Leading Strand

Synthesized continuously toward the replication fork

Lagging Strand

Synthesized discontinuously away from the fork in Okazaki fragments

Okazaki Fragments

Short DNA fragments formed on the lagging strand

Polymerase III

Main enzyme synthesizing Okazaki fragments

DNA Ligase

Seals Okazaki fragments into a continuous strand

Bidirectional Replication

Replication proceeds in two directions outward from the origin

Proofreading

DNA polymerase activity that detects and corrects mismatched bases

Mitosis/Meiosis

Cell divisions during which DNA must be replicated

Nucleosome

DNA wrapped around histone octamers for compaction

Histone Proteins

Form nucleosome core (H2A, H2B, H3, H4 ×2 each)

Chromatin

Packed DNA–protein complex inside the nucleus

Taq Polymerase

Heat-stable polymerase used in PCR