Topic 9 Mitosis Flashcards
Cellular Division
- The ability of organisms to produce more of their own kind
- The continuity of life is based on the reproduction of cells, or cell division
- Mitosis and Meiosis
Functions of Cellular Division
* In unicellular organisms:
- Division of one cell reproduces the
entire organism
- Multicellular eukaryotes depend on cell division for:
- Development from a fertilized egg
- Growth
- Repair
Cell cycle:
the life of a cell from formation to
its own division
daughter cells
Most cell division results in two daughter cells with identical genetic information
* The exception is meiosis:
Genome
all the DNA in a cell
* A genome can consist of:
* A single DNA molecule (common in prokaryotic cells)
* A number of DNA molecules (common in eukaryotic cells)
Chromatin
a complex of DNA and protein (histones) that condenses during cell division
Sister chromatids:
joined copies of the original chromosome, attached along their lengths by cohesins
Cohesins
protein complexes that attach sister chromatids
- The centromere:
- The narrow “waist” of the duplicated
chromosome - Where the two chromatids are most closely attached
- Once separate, the chromatids are called chromosomes
Interphase (G1, S, and G2)
- Cell growth and copying of chromosomes
in preparation for cell division
Mitotic phase (Mitosis and Cytokinesis)
- Mitosis: the division of the genetic material in the nucleus
- Cytokinesis: the division of the cytoplasm
G1 phase:
First gap, cells increase in size, gets ready for S phase
S phase:
Synthesis, DNA replication occurs
G2 phase
Second gap, cells continue to grow,
gets ready for Mitosis
G2 of Interphase (after s phase) 3
- A nuclear envelope enclose the nucleus
- Two centrosomes have formed
- Regions that organize microtubules
- Chromosomes duplicated in S phase cannot be seen, because they have not condensed
Prophase 4
- chromatin fibers are tightly coiled into discrete chromosomes, becoming visable
- duplicated chromosomes appear as two sister chromatids joined at centromeres
- mitotic spindle begins to form
- centrosomes move away from each other
prometaphase 5
- nuclear envelope fragments, chromosomes even more condense
- microtubules from each centresome invade nuclear area
- kinetochore on the centromere on each sister chromotid
- some microtubule become kinetochore microtubules, jerking chromosomes back and forth
- any non kinetochore microtubules elongate the cell
Metaphase 3
- Centrosomes now at opposite poles of the cell
- Chromosomes have arrived at the metaphase plate
- An imaginary plane at the middle of the cell * Centromeres lie at metaphase plate
- Kinetochore of each sister chromatid attach to kinetochore microtubules
Anaphase 4
- shorest phase of mitosis
- cohesios between chromotids are cleaved, allowing each pair to separate
- two new daughter chromosomes moving towards opposite poles
- centromeres lead, because microtubules attached to kinetochore
Telophase 4
- two daughter nuclei formm
- nuclear envelope reappears
- chromosomes start to decondense
- mitosis is complete
cytokinesis
- division of cytoplasm
- involves fomration of a cleavage furrow in animal cells
The Mitotic Spindle:
- A structure made of microtubules that controls chromosome movement during mitosis
centrosome
In animal cells, assembly of spindle microtubules begins in the centrosome
* Microtubule-organizing center (MTOC)
- the centrosome replicates during interphase
- two centrosomes migrate to oppoiste ends of the cell during prophase and prometaphase
Kinetochores
are protein complexes associated with centromeres
In anaphase, the cohesins are cleaved by
an enzyme called separase
The microtubules shorten by
depolymerizing at their kinetochore ends
Non-kinetochore microtubules
from opposite poles overlap and push against each other, elongating the cell
Non-kinetochore microtubules
from opposite poles overlap and push against each other, elongating the cell
In animal cells, cytokinesis occurs by…. In plant cells
a process known as cleavage, forming a cleavage furrow
* Contractile ring of microfilaments
a cell plate forms during cytokinesis
* Vesicles contain cell wall material
* Vesicles are derived f rom Golgi apparatus
cell cycle control system
The cell cycle is directed by a distinct cell cycle control system, which is similar to a clock
* The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received
Cellular Checkpoints
- Changes in regulatory protein concentrations drives the cell cycle
- Three important checkpoints are those in the G1, G2, and M phases
- If the cell does not receive the go- ahead signal, it will exit the cycle,
- Switches to an on-dividing state called the G0 phase v
