3. DNA replication Flashcards
DNA Replication:
Before entering Mitosis, cells create a copy of its genome.
* During S-Phase (Interphase)
S-Phase:
Beginning of Cell division
Semiconservative DNA Replication:
- Helix unwounds: New strands formed using old as template.
- Result: Two new helices with one old strand and one new strand.
Origin of Replication:
Start of DNA replication.
* Specific DNA sequence that recruits components to initiate transcription.
DNA Replication is BIDIRECTIONAL:
- Starts at one place and replicates in two directions.
- Replication bubbles can start replicating at different times.
DNA Polymerase:
Enzyme that adds nucleotides to a replicating strand. Synthesizes in 5’ - 3’.
* Catalyze formation of PHOSPHODIESTER BONDS between 5’ Phosphate group and 3’ OH group.
* NEEDS: Template strand, Primer, 3’ end to extend from
Helicase:
Enzyme that unwinds DNA template.
3’-5’ Exonuclease Activity:
In case of replicating error: allows DNA polymerase to chew back newly synthesized strand and correct error.
PCNA Primer:
Sliding Clamp. Clamps DNA to avoid derailing while replicating.
DNA Replication is Semidiscontinuous:
Leading strand replication is continuous while lagging strand replication is discontinuous.
* Because: DNA polymerase only synthesize 5’-3’. and DNA is antiparallel helix.
Primase:
Places RNA primers, 5’-3’.
Antiparallel to DNA template.
* Needed once for leading and Multiple for Lagging.
Ligase:
- Enzyme binds Okazaki fragments on lagging.
- Needed once for leading.
- Lagging connects to Leading.
DNA Replication is concurrent:
Leading and Lagging replicated at same rate
Enzyme Dimer:
Enzyme dimers of the replicative DNA polymerases are formed to synthesize both leading and lagging strands of DNA simultaneously at the replication fork.
