Ch 12 RQ
1.
2.
3.
4.
5.
What functions is MITOSIS used for in
the body?
What is ALL of the DNA in a cell known
as?
Nuclear division is also called ____.
The division of the cytoplasm is called
______.
What is the process by which gametes
are produced?
1. Describe the structural organization of
the genome.
Genome = the total hereditary endowment of
a cell
• Organized into functional units called
chromosomes (supercoiled DNA-protein
complexes of chromatin)
• The DNA exists in different phases at
different stages in the cell cycle 
2. Overview the major events of cell division
that enable the genome of one cell to be
passed on to two daughter cells.
1.
The complete genome is duplicated during
interphase
- these become sister chromatids (2
identical copies)
2. Cell division occurs after duplication in
two phases  nuclear and cytoplasm
(mitosis)
(cytokinesis) 
3. Describe how chromosome number changes
throughout the human life cycle.
1.
2.
3.
4.
5.
Individual inherits
46, 23 from each
parent
Meiosis halves
number to 23 (sperm
or ovum)
Fertilization (23 +
23 = 46)
Zygote has 46 new
chromosomes
Becomes an
individual 
4. List the phases of the cell cycle and
describe the sequence of events that occurs
during each phase.
A.
B.
Interphase  growth & metabolic activity
- 90% of cell cycle
1. G1 phase = growth
2. S phase = synthesis (duplication)
3. G2 phase = growth
Mitosis & Cytokinesis  nuclear & cytoplasmic division
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
6. Cytokinesis 
5. List and draw the phases of mitosis and
describe the events characteristic of each
phase.
Prophase
• Nucleoli disappear
• Chromatin
condenses into
chromosomes
• Spindle and
centrosomes form
(act as anchors) 
Prometaphase…
• Nuclear envelope
fragments
• Spindle fibers extend
• Kinetochore at the
centromere region
• Kinetochore
microtubules attach
• Nonkinetochore
radiate and overlap
with others 
Metaphase…
• Centrioles position
at opposite poles
• Chromosomes move
to the cell’s
equator and
centromeres align

Anaphase…
• Characterized by
movement
• Sister chromatids
split apart
• Kinetochore
microtubules shorten
• Poles move further
apart, elongating the
cell 
Telophase & cytokinesis…
• Nonkinetochore
microtubules elongate
cell
• Daughter nuclei begin
to form
• Nuclear envelopes
form
• Nucleoli reappear
• Chromosomes uncoil
• Cytoplasm divides 
•
•
•
•
6. Draw or describe the spindle apparatus
including centrosomes, nonkinetochore
microtubules, kinteochore microtubules, asters,
and centrioles (in animal cells).
The assembly of spindle microtubules begins in the
centrosome, or microtubule organizing center
Nonkinetochores elongate the whole cell during
anaphase
Kinetochores arrange
chromosomes and
align them
Centrioles  the center
of the centrosome
(not necessary and only
found in animal cells) 
7. Describe what characteristic changes
occur in the spindle apparatus during each
phase of mitosis.
Prophase spindle microtubules radiate out
Prometaphase  each chromatid develops
kinetochores
-spindles attach and become kinetochore
microtubules
Metaphase  all duplicated chromosomes align at
plate (equator)
Anaphase  centromeres split – microtubules direct
segregation; kinetochore microtubules shorten by
depolymerizing ends
Telophase  sets of chromosomes are clustered at
ends 
8. Explain the current models for poleward
chromosomal movement and elongation of the
cell’s polar axis.
• Kinetochore microtubules shorten at the
kinetochore end as chromosomes approach
poles
• Microtubules shorten by depolymerizing at
the ends; pulling chromosomes apart
The mechanism of this interaction may
involve microtubule-walking proteins that
“walk” a chromosome (between
kinetochores and microtubules) 
9. Compare cytokinesis in animals and plants.
-
Animals
process called
‘cleavage’
1. Cleavage furrow
forms a shallow
groove in the cell
surface
2. Contractile ring of
actin forms and
contracts
3. Parent cell pinches
into two
Plants
- cell plate grows and
eventually divides cell
into two joined cells 
10. Describe the process of binary fission in
bacteria and how this process may have
evolved to mitosis in eukaryotes.
• A process during which
bacteria replicate
their chromosomes
and equally distribute
the copies
• Preceded eukaryotic
cell division
- origins of mitosis 
11. Describe the roles of checkpoints, cyclin,
Cdk, and MPF, in the cell-cycle control
system.
• Checkpoints  ensure that appropriate
conditions have been met before the cycle
advances
• Cyclin  a class of regulatory proteins that
control cyclical changes in kinase activity
• CDKs  cyclin-dependent-kinases that
regulate the cell cycle when attached to a
particular cyclin
• MPF  maturation promoting factor –
controls the cell’s progress through the G2
checkpoint to mitosis 
12. Describe the internal and external
factors which influence the cell cycle control
system.
Internal
• Kinetochores signal
the M- phase
checkpoint about
chromosome –
spindle interactions
• All chromosomes
must be attached
External
• Chemical factors
- lack of essential
nutrients
- growth factors needed
• Physical factors
- crowding (densitydependent inhibition)
- need substrate
(anchorage-dependent
inhibition) 
13. Explain how abnormal cell division of
cancerous cells differs from normal cell
division.
• Cancer cells have escaped cell cycle
controls
- divide excessively
- do not respond to cell density or lack of
growth factors
- can make growth factors themselves
• Products of mutated or transformed
normal cells
• Spread of cancer is called metastasis 