CHAPTER 9
MITOSIS (CELL DIVISION) AND CELL CYCLE
ACTIVATOR—KWL CHART
What do
you know
about
mitosis?
MITOSIS
What do
you want
to know
about
mitosis?
What did I
learn
today
about
mitosis?
ACTIVATOR
Name the stages of
mitosis in order.
IMPACTS, ISSUES: HENRIETTA’S
IMMORTAL CELLS



Cancer cells isolated from Henrietta Lacks
established a self-perpetuating lineage of cancer
cells
The cell lineage, name HeLa cells, is used in
research laboratories across the world
Henrietta Lacks’ contribution is used to research
cancer, viral growth, protein synthesis, effects of
radiation, and more
Henrietta’s Immortal Cells
Fig. 9-2, p.141
UNDERSTANDING CELL DIVISION

“Omnis cellula e cellula”---ALL cells from cells

What instructions are necessary for inheritance?


How are those instructions duplicated for
distribution into daughter cells?
By what mechanisms are instructions parceled
out to daughter cells?
REPRODUCTION


Parents produce a new generation of cells or
multicelled individuals like themselves
Parents must provide daughter cells with
hereditary instructions, encoded in DNA, and
enough metabolic machinery to start up their
own operation
DIVISION MECHANISMS
Eukaryotic organisms

Mitosis(nuclear division) & cytokinesis (cytoplasm
division)

Meiosis—ch 10
Prokaryotic organisms

Prokaryotic fission—replicates only a small, single,
circular chromosome
HUMAN LIFE CYCLE
BOZEMAN VIDEO--MITOSIS
http://www.youtube.com/watch?v=1cVZBV9tD-A
ROLES OF MITOSIS


Multicelled organisms

Growth

Cell replacement
Some protistans, fungi, plants, animals

Asexual reproduction
CELL DIVISION

Individual cells of a human embryo divide,
developing from a paddlelike structure into a
hand
Cell
Division
Fig. 9-10, p.149
CHROMOSOME

A DNA molecule & attached proteins

Duplicated in preparation for mitosis
one chromosome (unduplicated)
one chromosome (duplicated)
Chromosome
a One chromosome (unduplicated)
one chromatid
one chromatid
two sister
chromatids
b One chromosome (duplicated)
Stepped Art
Fig. 9-3a, p.142
STRUCTURE OF CHROMOSOME PAIR
Sister chromatids
 Centromere
 locus

ORGANIZATION OF CHROMOSOMES
DNA
DNA and proteins
arranged as cylindrical fiber
one nucleosome
histone
CHROMOSOME NUMBER

Sum total of chromosomes in a cell

Somatic cells


Chromosome number is diploid (2n)

Two of each type of chromosome
Gametes

Chromosome number is haploid (n)

One of each chromosome type
THE CELL CYCLE
—ALTERNATES BETWEEN M (MITOSIS) PHASE
AND INTERPHASE
interphase
G1
S
Mitosis
telophas
e
anaphas
e
metaphas
e
prophas
e
G2
Figure 9.5
Page 144
INTERPHASE

Usually longest part of the cycle

Nondividing phase

Cell increases in mass (grows & PREPARES for
division)

Number of cytoplasmic components doubles

DNA is duplicated
G1—1st growth phase
 S– synthesis (DNA replicates)
 G2– 2nd growth phase; considered by some to be
the first phase of mitosis

MITOSIS
 Period
of nuclear division
 Usually
followed by cytoplasmic
division(cytokinesis)
 Four
stages:
Prophase
Metaphase
Anaphase
Telophase
CONTROL OF THE CYCLE

Once S begins, the cycle automatically runs
through G2 and mitosis

The cycle has a built-in molecular brake in G1

Cancer involves a loss of control over the cycle,
malfunction of the “brakes”
STOPPING THE CYCLE
 Some
cells normally stop in interphase

Neurons in human brain

Arrested cells do not divide
 Adverse

conditions can stop cycle
Nutrient-deprived amoebas get stuck in
interphase
THE SPINDLE APPARATUS


Consists of two distinct sets of microtubules

Each set extends from one of the cell poles

Two sets overlap at spindle equator
Moves chromosomes during mitosis
SPINDLE APPARATUS
one spindle pole
one of the
condensed
chromosomes
spindle equator
microtubules
organized
as a spindle
apparatus
one spindle pole
MAINTAINING
CHROMOSOME
NUMBER
chromosome
(unduplicated) in cell at
interphase
same chromosome
(duplicated) in
interphase prior to
mitosis
mitosis, cytoplasmic division
chromosome
(unduplicated)
in daughter
cell
at interphase
chromosome
(unduplicated)
in daughter
cell
at interphase
1
2
3
6
7
8
13
14
15
19
20
21
4
9
10
16
22
5
11
12
17
18
MAINTAINING
CHROMOSOME
NUMBER
XX (or XY)
Fig. 9-6a, p.145
Maintaining
Chromosome Number
a Two of the
chromosomes
(unduplicated)
in a parent cell
at interphase
b The same two
hromosomes, now
duplicated, in that
cell at interphase,
prior to mitosis
c
c Two chromosomes
(unduplicated) in the
parent cell’s daughter
cells, which both start
life in interphase
Fig. 9-6b, p.145
pol
e
Maintaining
Chromosome
Number
pole
microtubule of
bipolar spindle
p.145
STAGES OF MITOSIS
Prophase
Metaphase
Anaphase
Telophase
EARLY PROPHASE MITOSIS BEGINS
Duplicated chromosomes begin to condense and become
observable under a microscope; mitotic spindle
forms
Figure 9.7
Page 146
LATE PROPHASE—AKA PROMETAPHASE
 New
microtubules are
assembled
 One
centriole pair is
moved toward opposite
pole of spindle
 Nuclear
envelope starts
to break up
Figure 9.7
Page 146
TRANSITION TO METAPHASE
Spindle forms
Spindle
microtubules
become attached to
the two sister
chromatids of each
chromosome
Figure 9.7
Page 146
METAPHASE
All chromosomes are
lined up at the spindle
equator
 Chromosomes are
maximally condensed

Figure 9.7
Page 147
ANAPHASE
Characterized by
MOVEMENT!
 Sister chromatids of each
chromosome are pulled
apart thus elongating the
cell
 Once separated, each
chromatid is a
chromosome
 Kinetechore vs.
nonkinetechore
microtubles

Figure 9.7
Page 147
TELOPHASE


Chromosomes loosen and
become less distinct
Two nuclear membranes
form, one around each set of
unduplicated chromosomes
 Cytokinesis
starts to
produce 2 identical
daughter cells

Plasmodia—when some slime
molds have NO cytokinesis
resulting in mulitnucleated
masses
Figure 9.7
Page 147
RESULTS OF MITOSIS
Two daughter nuclei
 Each with same
chromosome number as
parent cell
 Chromosomes in
unduplicated form

Figure 9.7
Page 147
a Cell at Interphase
The cell
duplicates its
DNA, prepares Mitosis
for nuclear
pair of
division
centrioles
nuclear
envelop
chromosomes
b EARLY PROPHASE
Mitosis begins. The DNA
and its associated proteins
have started to condense.
The two chromosomes
color-coded purple were
inherited from the female
parent. The other two
(blue) are their
counterparts., inherited
from the male parent.
c LATE PROPHASE
Chromosomes
continue to
condense. New
microtubules
become assembled.
They move one of
the two pairs of
centrioles to the
opposite end of the
cell. The nuclear
envelope starts to
d TRANSITION TO
METAPASE
Now microtubules
penentrate the nuclear
region. Collectively,
they form a bipolar
spindle apparatus.
Many of the spindle
microtubules become
attatched to the two
sister chromatids of
each chromosome.
Fig. 9-7a, p.146
microtubule
e METAPHASE
All chromosomes have
become lined up at the
spindle equator. At this
stage of mitosis (and of
the cell cycle), they are
most tightly condensed
f ANAPHASE
Attachments between
the two sister
chromatids of each
chromosome break.
The two are separate
chromosomes, which
microtubules move to
opposite spindle pores.
g TELOPHASE
There are two clusters
of chromosomes, which
decondense. Patches of
new membrane fuse to
form a new nuclear
envelope. Mitosis is
completed.
h INTERPHASE
Now there are two
daughter cells.
Each is diploid; its
nucleus has two of
each type
of chromosome,
just like the
parent cell.
Fig. 9-7b, p.146
ANIMAL CELL DIVISION—
CLEAVAGE FURROW FORMS AT OLD METAPHASE
PLATE BY WAY OF AN ACTIN CONTRACTILE RING
Animal Cell Division—
1 Mitosis is
over, and the
spindle is
now
disassembling
.
2 At the former
spindle equator,
a ring of microfilaments
attached to the
plasma
membrane
contracts.
3 As its
diameter
shrinks, it
pulls the cell
surface
inward.
4
Contractions
continue; the
cell is
pinched in
two.
Fig. 9-8a, p.148
Cell Plate Formation
cell
plane
formin
g
1 As mitosis
ends, vesicles
cluster at the
spindle equator.
They contain
materials for
anew primary
cell wall.
2 Vesicle membranes
fuse. The wall
material is
sandwiched between
two new membranes
that lengthen along
the plane of a newly
forming cell plate.
3 Cellulose is
deposited inside
the sandwich. In
time, these deposits
will form two cell
walls. Others will
form the middle
lamella between
the walls and
cement them
together.
4 A cell plate
grows at its
margins until it
fuses with the
parent cell plasma
membrane. The
primary wall of
growing plant
cells is still thin.
New material—
cellulose- is
deposited on it.
Fig. 9-8b, p.148
MITOTIC CONTROL



Growth factors—such as needed nutrients
Density-dependent inhibition—overcrowding=less
growth
Checkpoint(restriction point)—Ex: cells have a
checkpoint in G1 where cell can either go on with cycle
or go into G 0 (this is where mature muscle and nerve
cells are)
CONTINUED MITOTIC CONTROL
CYCLIN-DEPENDENT KINASES-AKA Cdks
 enzymes(proteins) which are affected by the cell
cycle regulatory protein cyclin; when these
enzymes are active & attached to cyclin, then
mitosis can happen)
 Ex: MPF (maturation promoting factor)

CELL CYCLE & RELATIVE CYCLIN
CONCENTRATION
TUMORS



Sometimes a checkpoint gene mutates and
control over cell division is lost.
Cells uncontrollable division forms an abnormal
mass called a tumor.
Neoplasms
Cancer
Fig. 9-12, p.150
MALIGNANT VS. BENIGN (SEE P. 151)
cell at
interphase
nucleus
cytoplas
m
telophas
e
prophas
e
anaphas
e
metaphas
e
Fig. 9-15, p.153