Topic 2 notes
Cell division
2.5.1 Outline the stages in the cell cycle, including
interphase ( G1, S, G2 ) mitosis and cytokinesis
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Cell cycle: the life cycle of a typical cell. After
cytokinesis, or splitting into two cells, the cells must
grow ( G1 )
Note that some cells simply live after growing to full
size, they do not prepare for additional divisions, they
are said to be in G0 phase.
S-phase is where DNA is replicated in preparation for
the next cell division
G2 phase is where the cell prepares for mitosis,
mitochondria, and other organelles are replicated.
Mitosis is the dance of the chromosomes. The DNA
information needs to be equally divided between the two
daughter cells. It is a continuous process that is
artificially divided into 4 phases.
Prophase: Chromosomes become visible by coiling
around histones. Nuclear membrane dissolves, spindle
starts to form. Centromeres are proteins that join exact
copies of DNA together ( Chromatids).
Metaphase: Spindle fibers have started to shorten
and they line the chromosomes up down the middle of
the spindle.
Anaphase: Centromeres separate and exact copies
of DNA are drawn to opposite sides of the spindle.
Telophase: Chromosomes have reached the spindle
end, new nuclear membranes form around the bundled
chromosomes.
Cytokinesis: is the actual splitting of the cell into two
daughter cells. In plants, a cell plate forms first. In
animals, a cleavage furrow forms that gradually divides
the cells.
2.5.2 State that tumors ( cancers) are the result of
uncontrolled cell division and that these can occur in any
organ or tissue.
A cell that constantly copies itself can sometimes be
called cancerous, especially if it no longer differentiates
into a specific kind of cell. Chemo therapy is a drastic
method of stopping all cell division in your body.
Cancer cells hopefully die before you do. Hair stops
growing, skin stops replacing, you are in suspended
animation for a while.
2.5.3 State that interphase is an active period of life of a
cell when many metabolic reactions occur, including
protein synthesis, DNA replication and an increase in the
number of mitochondria and/or chloroplasts.
2.5.4 Describe the event that occur in the four phases of
mitosis ( prophase, metaphase, anaphase and telophase)
Include supercoiling around histone proteins,
attachment of spindle microtubules to the centromeres,
the splitting of the centromeres, movement of sister
chromosomes to opposite poles, and breakage and reformation of nuclear membranes.
2.5.5 Explain how mitosis produces two genetically
identical nuclei.
During S phase all the chromosomes have exact
copies of themselves made. These copies are attached
together by the protein centromere. Each individual
copy is called a chromatid. Mitosis is the mechanism for
assuring that each daughter cell receives one copy of
each chromosome.
2.5.6 State that growth, embryonic development, tissue
repair and asexual reproduction involve mitosis.
Mitosis creates exact copies of the original cell.
This is how multicellular animals grow and organisms
repair themselves. Meiosis is the special division that
creates sexual reproduction cells, or gametes.