DNA replication, the cell cycle and mitosis Flashcards
Initiation steps of DNA replication
- Topoisomerase unwinds DNA.
- DNA helicase unzips two strands, uses ATP to break H bonds between base pairs.
Leading strand synthesis process
- RNA primer placed at origin of replication
- DNA polymerase adds to RNA primer and synthesises continuously in a 5’ to 3’ direction.
- RNA primer is removed
Lagging strand synthesis process
- DNA primase synthesises multiple short RNA fragment primers
- DNA polymerase adds to RNA primer, starting Okazaki fragment
- Ribonuclease removes RNA primer after fragment completion.
- Repair DNA polymerase replaces RNA with DNA
- DNA ligase joins the two fragments together using ATP to make newly synthesised strand continuous
Name of starting point for replication
Origin of replication
Name of site of DNA synthesis
Replication fork
Role of sliding clamp in DNA replication
Ensures DNA polymerase stays attached during synthesis
Role of single-stranded DNA-binding proteins in DNA replication
Ensures DNA remains extended for replication
What is semi-conservative replication
Double-stranded daughter copies of parental DNA are made up of one strand from the parental DNA and a newly synthesised strand, complementary to the parental strand.
Process of proof-reading and correction in DNA replication
- Before a new nucleotide is added, previous nucleotide is checked for correct base-pairing
- Any incorrect bases are removed by 3’ to 5’ (opposite direction to synthesis) exonuclease activity of DNA polymerase
- New correct nucleotide added
Process of eukaryotic chromosome replication (and diagram see notes)
- Eukaryotic chromosomes are linear and very long
- Multiple origins of replication established around 100 kilo base pairs apart
- Each replication origin gives bi-directional replication forks
- Replication forks eventually meet to synthesis entirely new chromosome
E.coli chromosome replication process (and diagram see notes)
- Replication starts at unique origin
- Two replication forks proceed simultaneously in opposite directions
- Bacterial chromosomes are circular and continuous so replication forks eventually meet at the other side of the chromosome to where the origin is located
List cell cycle phases in order
M phase G1 phase - G0 phase S phase G2 phase
M phase features
Mitosis and cell division
G1 phase features
Gap phase 1
DNA in the form of a single linear double helix
S phase features
Synthesis phase
DNA synthesis and replication takes place
G2 phase features
Gap phase 2
Each chromosome has two identical sister chromatids produced by S phase ready for mitosis (M phase)
G0 phase features
Exits from G1 phase
Cells which have stopped dividing, apoptotic cells etc.
Mitosis phases in order
Prophase Metaphase Anaphase Telophase Cytokinesis Interphase
Late prophase chromosome condition
Chromosomes condensed, each contains two sister chromatids
Metaphase chromosome condition
Chromosomes condensed, now aligned on the central plane of the spindle
Anaphase chromosome condition and process
Sister chromatids move to opposite poles of spindle. Centromere splits, ensuring each new cell gets one half of new chromosomes
Telophase chromosome condition and process
Two daughters cells formed with half of total chromosomes in each
Cytokinesis process
Division of cytoplasm
Interphase G1 begins after telophase, main feature
Condensation of chromosomes is reversed
