Chapter 5c
Cell Division and Mitosis
Division Mechanisms
Eukaryotic organisms
– Mitosis
– Meiosis
Prokaryotic organisms
– Prokaryotic fission`
Roles of Mitosis
• 1) Multicelled organisms
– a) Growth
– b) Cell replacement
• 2) Some protistans, fungi, plants, animals
– a) Asexual reproduction`
Chromosome
• 1) A DNA molecule & attached proteins
• 2) Duplicated in preparation for mitosis`
one chromosome (unduplicated)
one chromosome (duplicated)
Chromosome Number
• 1) Sum total of chromosomes in a cell
• 2) Somatic cells
– a) Chromosome number is diploid (2n)
– b) Two of each type of chromosome
• 3) Gametes
– a) Chromosome number is haploid (n)
– b) One of each chromosome type`
Human Chromosome Number
• 1) Diploid chromosome number (n) = 46
• 2) Two sets of 23 chromosomes each
– a) One set from father
– b) One set from mother
• 3) Mitosis produces cells with 46
chromosomes--two of each type`
Cell Cycle
• 1) Cycle starts when a new cell forms
• 2) During cycle, cell increases in mass
and duplicates its chromosomes
• 3) Cycle ends when the new cell
divides`
Interphase
• 1) Usually longest part of the cycle
• 2) Cell increases in mass
• 3) Number of cytoplasmic components
doubles
• 4) DNA is duplicated`
Stages of Interphase
• 1) G1
– a) Interval or gap after cell division
• 2) S
– a) Time of DNA synthesis (replication)
• 3) G2
– a) Interval or gap after DNA replication`
Mitosis
• 1) Period of nuclear division
• 2) Ending with telophase and
cytoplasmic division
• 3) Four stages:
– a) Prophase
– b) Metaphase
– c) Anaphase
– d) Telophase`
The Spindle Apparatus
• 1) Consists of two distinct sets of
microtubules
– a) Each set extends from one of the cell
poles
– b) Two sets overlap at spindle equator
• 2) 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
Early Prophase Mitosis Begins
1) Duplicated chromosomes begin to
condense``
Late Prophase
• 1) New microtubules
are assembled
• 2) One centriole pair
is moved toward
opposite pole of
spindle
• 3) Nuclear envelope
starts to break up`
Prometaphase
• 1) Spindle forms
• 2) Spindle
microtubules
become attached to
the two sister
chromatids of each
chromosome`
Metaphase
• 1) All
chromosomes are
lined up at the
spindle equator
• 2) Chromosomes
are maximally
condensed`
Anaphase
• 1) Sister
chromatids of
each chromosome
are pulled apart
• 2) Once
separated, each
chromatid is a
chromosome `
Telophase
• 1) Chromosomes
decondense
• 2) Two nuclear
membranes form,
one around each
set of unduplicated
chromosomes`
Results of Mitosis
• 1) Two daughter
nuclei
• 2) Each with same
chromosome
number as parent
cell
• 3) Chromosomes in
unduplicated form`
MITOSIS
pair of
centrioles
plasma
membrane nucleus
CELL AT INTERPHASE
The cell duplicates its
DNA, prepares for
nuclear division
nuclear
envelope
chromosomes
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.
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 break up.
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.
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
ANAPHASE
Attachments between the
two sister chromatids of each
chromosome break. The two
are separate chromosomes,
which microtubules move to
opposite spindle pores.
TELOPHASE
There are two clusters
of chromosomes, which
decondense. Patches of
new membrane fuse to form
a new nuclear envelope.
Mitosis is completed.
INTERPHASE
Now there are two
daughter cells. Each
is diploid; its nucleus
has two of each type
of chromosome, just
like the parent cell.
Cytoplasmic Division
• 1) Usually occurs between late
anaphase and end of telophase
• 2) Two mechanisms
– a) Cell plate formation (plants)
– b) Cleavage (animals)`