- Cell Cycle: is a highly regulated series of events for the growth and reproduction of eukaryotic cells
- Three stages: Interphase, Mitosis, & Cytokinesis
- Smaller cells better because easier to coordinate chromosomes and microtubules with less ATP
- DNA content doubles during Interphase (S phase) and halves during mitosis
Cell Cycle: Summary
Interphase
- Majority of cell cycle, split into 3 phases
- All have metabolic activity & growth
- All have metabolic activity & growth
G1 Phase
- Metabolic activity and growth; one chromatid
S Phase
- DNA replication; two chromatids
G2 Phase
- Prepares for cell division
M phase
- Mitosis and cytokinesis
The G0 Cycle
- If the cell does not receive the go ahead signal, it will exit the cycle, switching to a nondividing state called the G0 phase.
- Can re-enter the cell cycle in response to appropriate cues.
- Nondividing cells may exit the cell cycle or be held at a particular stage in it
How Does Mitosis Produce 2 Identical Daughter Cells
- DNA Replication (Interphase) and separation of chromatids (Anaphase)
- Once duplicated, a chromosome consists of two sister chromatids, connected along their entire length
- Before a cell divides, sister chromatids become individual chromosomes → ensure that daughter cells get a complete/identical set of chromosomes
- Sister chromatids attached by cohesins and held most tightly by centromere: region of repetitive DNA sequences and proteins
- Count chromosomes by number of centromeres but chromatids are double
MITOTIC SPINDLE
- Consists of mitotic fibers, centrosomes, and asters
- Fibers made up of microtubules and proteins: control chromosome movement
- Elongate by adding tubulin
- Asters: microtubules that hold together two centrioles to make a centrosome
- Spindle is complete when asters elongate and touch membrane
- Two kinds of microtubules:
- Kinetochore Microtubules: attach to kinetochores → move chromosomes to metaphase plate → jerk chromosomes back and form
- Non-kinetochore microtubules: interact/overlap → elongate the cell as motor proteins push them from opposite poles using ATP
- Fibers made up of microtubules and proteins: control chromosome movement