
3.a.2 – In eukaryotes, heritable information is
passed to the next generation via processes
that include the cell cycle and mitosis, or
meiosis plus fertilization (12.1-12.3).
1.
2.
3.
4.

Reproduction (uni vs. multi)
Growth
Repair/replace old or damaged cells
To distribute identical genetic material to
two new daughter cells
Goal: To split the sister chromatids and give
one to each new cell – to make two new cells
with the correct amount of genetic info
1.
Somatic
 Non-sex cells (all body cells EXCEPT sex)
 Ex: red blood, skin, muscle
2.
Sex
 Otherwise known as gametes
 Ex: sperm, egg
The cell's hereditary endowment of DNA
Usually packaged into chromosomes
(easier to manage during the cell cycle)
 Prokaryotes:


 Single stranded, in cytoplasm, circular in shape

Eukaryotes:
 Double stranded, in nucleus, helix/spiral in shape

Made of a DNA and protein complex called
chromatin


During cell division, the chromatin becomes
highly condensed into the chromosomes
# of chromosomes:
 Sex cell (haploid cell)
▪ 23 (no pairs)—only contains one set of chromosomes
 Somatic cell (diploid cell)
▪ 46 (in 23 pairs)—contain two sets of chromosomes
 Chromatin
 Long, thin fiber
 Uncondensed
 Before/after cell division
 Genetic material usually in this form
 Chromosome
 Characteristic “X” shape
 Condensed into this shape
 Only during cell division
At cell division, each chromosome has
been duplicated
 The duplicated chromosome consists of
two sister chromatids
 Centromere – the point where two
sister chromatids are connected

1. Interphase - (90% of cycle) - when the
cell grows and duplicates the
chromosomes
2. Mitotic Phase (M) - when the
chromosomes are split into separate
cells
 In order:
 G1 - first gap
 S - synthesis
 G2 - second gap

G1:
 Cell grows and carries out regular
biochemical functions

S:
 DNA is replicated or synthesized -
chromosomes are replicated

G2:
 Cell completes preparations

Comment: A cell can complete S, but fail
to enter G2.
1. Mitosis - division of replicated
chromosomes
2. Cytokinesis - division of the cell’s
cytoplasm
To divide the 2 copies of the DNA
equally
 To separate the sister chromatids into
separate cells

Prophase
Prometaphase
Metaphase
4. Anaphase
5. Telophase
1.
2.
3.
Nucleoli disappear
Chromatin condenses into
chromosomes
 Centrioles separate to opposite ends
of the cell
 Mitotic spindle begins to form


 Nuclear envelope dissolves
 Spindle fibers join with the
kinetochore of the centromeres
Centrioles now at opposite ends of the
cell
 Chromosomes line up on the metaphase
plate
 Spindle apparatus fully developed

Centromeres break and the duplicate
chromosomes are pulled away from
each other toward opposite ends of the
cell
 Cell elongates; poles move slightly
further apart

Specialized regions of the centromeres
where spindle microtubules attach
 Appear to “ratchet” the chromosome
down the spindle fiber microtubule using
a motor protein
 Microtubules dissolve behind the
kinetochore

Chromosomes uncoil back to chromatin
Nuclear envelope reforms
Nucleoli reappear
 Spindle fibers disappear
 Cytokinesis usually starts




Animal
 Cleavage furrow forms
 Microfilaments contracts and divides the
cytoplasm into two parts

Plant
 Cell plate develops in between the two new
daughter cells (from Golgi vesicles)
 New cell wall developed around the cell plate
Plant Cell - Mitosis

Hypothesis: Mitosis has origins in
prokaryotic cells
 How do we know this?
▪ Proteins involved are identical
▪ Ex: kinetochores, protein kinase checkpoints,
etc.


Must be controlled
Rate of cell division depends on the cell
type
 Ex - skin: frequently
 liver - as needed
 brain - rarely or never



A critical control point in the cell cycle
Several are known
Cells must receive a “go-ahead” signal
before proceeding to the next phase
Also called the “restriction point” in
mammalian cells
 Places cells in a non-dividing phase
called the Go phase

GO



Non-dividing state
Most cells are in this state
Some cells can be reactivated back into
M phase from the Go phase
Uses protein kinases to signal “goahead” for the G2 phase
 Activated by a protein complex whose
concentration changes over the cell
cycle

GO
Protein
Kinase
 M-phase Promoting Factor
 Protein complex required for a cell to
progress from G2 to Mitosis
 Role of MPF - to trigger a chain of
protein kinase activations
 Active MPF has: cdk and cyclin
GO
MPF
Protein
Kinase

CDK:
 Protein Kinase
 Amount remains constant during cycle
 Inactive unless bound with cyclin

Cyclin:
 Protein whose concentration builds up over G1, S
and G2
 When enough cyclin is present, active MPF is
formed
Triggers Mitosis
Activates a cyclin-degrading enzyme,
which lowers the amount of cyclin in
the cell
 Result - no active MPF to trigger
another mitosis until the cycle is
repeated




External signals that affect mitosis
Examples:
 PDGF
 Density-dependent inhibition
 Anchorage dependence
PlateletDerived
Growth
Factor
 Stimulates
cell division
to heal
injuries


The number of cells in an area force
competition for nutrients, space, and
growth factors
 When density is high  no cell division
 When density is low  cells divide
Inhibition of cell division unless the cell
is attached to a substratum
 Prevents cells from dividing and floating
off in the body



Do not stop dividing.
The control mechanisms for cell
division have failed
Regulation of cell division is a balance
between:
Mitosis - making new cells
Apoptosis - cell suicide
 Cancer can result if either process
doesn’t work









Identify the roles of cell division
Identify the composition of a chromosome.
Recognize the phases of the cell cycle.
Identify the stages and characteristics of
Interphase.
Identify the stages and characteristics of
Mitosis.
Recognize the mechanisms of Cytokinesis.
Recognize factors that control cell division.
Recognize the results when the regulation of
cell division goes wrong.