BISC 101 Lecture Notes - Lecture 4: Helicase, Exonuclease, Primase

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Cell Cycle: Formation of a eukaryotic cell through duplication of its chromosomes until
Phases: 4 stages
Mitotic (M) Phase: Dividing Phase
Chromosomes as discrete structures when they condensed into compact
Interphase: Nondividing Phase BUT DNA replication (No dramatic
change/chromosomes uncoil into long/thin structures)
In the nucleus where histone (protein) with DNA
Called chromatin because can’t distinguish chromosomes
G1 (First Gap) Phase: Provides time required for parent cell to grow large
enough, synthesize enough organelles that it’s daughter cell can be normal in
G1 Checkpoint: Cell continues in cycle/divides OR exits the cell and
enters G0
Depends on Size/Availability of nutrients/Social
signals/Damage on DNA
Environment favourable
Prevents growth of mature cells that are in G0 phase
P53 (protein): Regulatory protein called tumour suppressors
that activate genes that stop the cell cycle until damage can be
S Phase: Replication of genetic material is separated from the partitioning of
chromosomes during M phase
G2 (Second Gap) Phase: Same as first gap
G2 Checkpoint: MPF (mitosis promoting factors) triggers and
Are all DNA replicated/repaired
Metaphase Checkpoint: If not all chromosomes are attached
properly to spindle apparatus, M phase arrests (stops) here
If not, some chromosomes might not separate
properly/daughter cells would have too many OR not enough
Cell-cycle checkpoints: Critical point in cell cycle that is regulated/Prevent division
of cells that are damaged
Interactions among regulatory molecules at each checkpoint allows a cell to
decide to proceed with division
Cells may divide uncontrollably/checkpoint fail if regulatory molecules
are defective
Types of Macromolecules involved:
Cohesins (Protein): Protein rings that hold sister chromatids until signal
Condensins (Protein): Protein rings that condense chromosomes (stabilize loops in
Nuclear Lamins : Mesh of intermediate filaments that give nucleus its shape
Form interface between chromosomes AND inside of nuclear envelope
Microtubules: Moves chromosomes to poles
Defects of cancer cells:
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