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Notes: Chapter 12 The Cell Cycle
1. General Purpose and Process
a. Cell division functions in reproduction, growth, and tissue renewal
b. A cell copies its chromosomes (composed of DNA), allocates them equally to
opposite ends of the cell, and then separates into 2 identical daughter cells.
c. Genome is a cell’s endowment of DNA.
2. Mitosis
a. Every species has a characteristic number of chromosomes
b. ex) Human somatic cells have 46 (Egg and sperm cells have 23 chromosomes)
c. centromere = a narrow waist in the chromosome.
d. Chromatin = Long strands of DNA and protein
i. (It is continually folded to form chromosomes)
e. Labeled Replicated Chromosome Diagram:
f.
The Mitotic Cell Cycle (Like a clock) (Figure 12.4)
i. Interphase (90% of cell’s life) *Growth occurs throughout Interphase
1. G1 – Growth - Cell makes proteins and reproductive organelles
like centrosomes.
2. S – Chromosomes duplicated: ‘S’ stands for synthesis
3. G2 – Growth: Final preparations for division
ii.
Mitotic Phase or M Phase (The division of the nucleus, Figure 12.5)
1. Prophase
a. Chromosomes condense
b. Nucleoli disappear
c. Mitotic spindle begins to form
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d. Chromosomes move away from each other
2. Prometaphase
a. Nuclear envolope fragments
b. Spindle invades nuclear area and interacts with the
chromosomes
c. Centrosomes continue to move toward opposite poles
d. Some microtubules attach to kinetochores and jerk
chromosome
3. Metaphase
a. Centrosomes are now at opposite poles
b. Chromosomes lie on the metaphase plate – an
imaginary plane between the spindle’s two poles.
c. Each chromatid’s kinetochore is attached to
microtubules
d. Entire apparatus of microtubules= spindle
4. Anaphase
a. Paired centromeres of each chromosome separate
b. New chromosomes begin to move to opposite poles as
their kinetochore microtubules shorten
c. At the end, poles have equal and complete collections
of chromosomes
5. Telophase and Cytokinesis (Division of the cytoplasm)
a. nonkinetochore microtubules continue to elongate cell
b. Two daughter nuclei form at the two poles of the cell
c. Chromosomes become less tightly coiled
d. In animal cells, a cleavage furrow forms
e. In plant cells, a cell plate forms
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3. Regulation of the Cell Cycle
a. Cell cycle control system – a cyclically operating set of molecules that triggers
and coordinates key events in the cell cycle.
b. Cell Cycle Checkpoints – a crucial control point where stop and go signals
regulate the cycle.
c. Controlled by internal and external growth cues
ex) Cytoplasmic proteins that promote cell division
ex) density- dependent inhibition – crowded cells stop dividing.
4. MPF (maturation promoting factor)
a. It is a kinase protein (one that switches target cell cycle proteins on or off by
phosphorylating them)
b. The two protein components of MPF are:
a) Cdks (cyclin-dependent kinase)- a cell division
control protein is active only when it is bound
to cyclin.
b) cyclin- a protein whose amount varies
cyclically, when it is in abundance, it binds to
cdk to make active MPF
c. It promotes entrance into mitosis from the M phase by phosphorylating
multiple proteins including one that leads to the destruction of cyclin itself