Cell division/Mitosis



http://www.patana.ac.th/Secondary/science/c4b/2/cell2.5.htm

2.5.1 Outline the stages in the cell cycle


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G stages are growth stages

S stage: replication of the double helix occurs.



The double helix is unzipped by helicase and a new complementary copy of the chromosome is formed. The copies stay attached by the centromere until they separate during mitosis. This ensures that each body cell has exact genetic copies.
Below is a diagram showing the a) the original chromosome and b) copied chromosome (two chromotids).


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2.5.2 State that tumors are the result of uncontrolled cell division



2.5.3 State that interphase is the active period in the life of the cell

G stages are growth stages, while S stage replicates the chromosmes ready for cell division (mitisis)

2.5.4 Describe the events in the stages of mitosis



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Interphase * is the "resting" or non-mitotic portion of the cell cycle.
  • It is comprised of G1, S, and G2 stages of the cell cycle.
  • DNA is replicated during the S phase of Interphase
Prophase
Prophase

Prophase
Prophase

Prophase - the first stage of mitosis. * The chromosomes condense and become visible
  • The centrioles form and move toward opposite ends of the cell ("the poles")
  • The nuclear membrane dissolves
  • The mitotic spindle forms (from the centrioles in animal cells)
  • Spindle fibers from each centriole attach to each sister chromatid at the kinetochore
Compare Prophase to the Prophase I and to the Prophase II stages of mitosis.
Metaphase* The Centrioles complete their migration to the poles
  • The chromosomes line up in the middle of the cell ("the equator")
Compare Metaphase to the Metaphase I and to the Metaphase II stages of mitosis.
Metaphase
Metaphase

Metaphase
Metaphase

Anaphase
Anaphase

Anaphase
Anaphase

Anaphase* Spindles attached to kinetochores begin to shorten.
  • This exerts a force on the sister chromatids that pulls them apart.
  • Spindle fibers continue to shorten, pulling chromatids to opposite poles.
  • This ensures that each daughter cell gets identical sets of chromosomes
Compare Anaphase to the Anaphase I and to the Anaphase II stages of mitosis.
Telophase* The chromosomes decondense
  • The nuclear envelope forms
  • Cytokinesis reaches completion, creating two daughter cells
Compare Telophase to the Telophase I and to the Telophase II stages of mitosis.
Telophase
Telophase

Telophase
Telophase


Cytokinesis Divides the Cytoplasm

In animal cells, cytokinesis occurs by a process known as cleavage


2.5.5 Explain how mitosis produces two genetically identical cells


DNA replication is complementary and semiconservative thus producing chromosomal copies that remain attached by the centromere until they separate by disjunction during metaphase. This ensures identical chromosme sets in the daughter cells. See diagrams above.

2.5.6 State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis