Transcript Metaphase - Faperta UGM

Cell Cycle,
Cell Division and Mitosis
1
Phases of the Cell Cycle
The cell cycle consists of
– Interphase – normal cell activity
– The mitotic phase – cell division
INTERPHASE
Growth
G1
(DNA synthesis)
Growth
G2
2
Cell Division



All cells are derived from pre-existing
cells
New cells are produced for reproduction,
growth and to replace damaged or old cells
Differs in prokaryotes (bacteria) and
eukaryotes (protists, fungi, plants, &
animals)
3
Functions of Cell Division
(a) Reproduction. An amoeba,
a single-celled
eukaryote, is
dividing into two cells. Each
new cell will be an individual organism
(b) Growth and development. This micrograph
shows a sand dollar embryo shortly after the
fertilized egg divided, forming two cells (LM)
(c) Tissue renewal. These dividing bone marrow
cells (arrow) will give rise to new blood cells
(LM).
4
Cell Division
•
•
•
An integral part of the cell cycle
Results in genetically identical daughter
cells
Cells duplicate their genetic material
–
Before they divide, ensuring that each
daughter cell receives an exact copy of the
genetic material, DNA
5
Cell Devision


DNA must be copied or
replicated before cell
division
Each new cell will then
have an identical copy of
the DNA
6
Identical Daughter Cells
Two
identical
daughter
cells
Parent Cell
7
Prokaryotic Chromosome
The DNA of
prokaryotes (bacteria) is
one, circular
chromosome attached
to the inside of the cell
membrane
8
Eukaryotic Chromosomes



All eukaryotic cells store
genetic information in
chromosomes
Each chromosome is
composed of a single, tightly
coiled DNA molecule
Chromosomes can’t be seen
when cells aren’t dividing and
are called chromatin
9
9
Chromatids

Duplicated
chromosomes are
called chromatids &
are held together by
the centromere
Called Sister Chromatids
10
Chromosomes
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
11
Homologues Chromosome
•
•
•
•
Look the same
Control the same traits
May code for different forms of each trait
Independent origin - each one was inherited from a
different parent
12
Chromosome Duplication
•
•
In preparation for cell division, DNA is replicated and the
chromosomes condense
Each duplicated chromosome has two sister chromatids, which
separate during cell division
0.5 µm
A eukaryotic cell has multiple
chromosomes, one of which is
represented here. Before
duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosome
consists of two sister chromatids
connected at the centromere. Each
chromatid contains a copy of the
DNA molecule.
Mechanical processes separate
the sister chromatids into two
chromosomes and distribute
them to two daughter cells.
Chromosome
duplication
(including DNA
synthesis)
Centromere
Separation
of sister
chromatids
Sister
chromatids
13
Centrometers
Sister chromatids
Chromosome Duplication
•
•
Because of duplication, each condensed chromosome
consists of 2 identical chromatids joined by a centromere.
Each duplicated chromosome contains 2 identical DNA
molecules (unless a mutation occurred), one in each
chromatid:
Non-sister
chromatids
Centromere
Duplication
Sister
chromatids
Two unduplicated
chromosomes
Sister
chromatids
Two duplicated chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
14
Structure of Chromosomes
•
•
The centromere is a constricted region of the chromosome
containing a specific DNA sequence, to which is bound 2 discs of
protein called kinetochores.
Kinetochores serve as points of attachment for microtubules that
move the chromosomes during cell division:
Metaphase chromosome
Centromere
region of
chromosome
Kinetochore
Kinetochore
microtubules
Sister Chromatids
15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structure of Chromosomes
–
–
Diploid - A cell possessing two copies of each chromosome (human
body cells).
Homologous chromosomes are made up of sister chromatids joined
at the centromere.
Haploid - A cell possessing a single copy of each chromosome
(human sex cells).
16
Types of Cell Reproduction




Asexual reproduction involves a single cell
dividing to make 2 new, identical daughter
cells
Mitosis & binary fission are examples of
asexual reproduction
Sexual reproduction involves two cells (egg
& sperm) joining to make a new cell (zygote)
that is NOT identical to the original cells
Meiosis is an example of sexual reproduction
17
Cell Division in Prokaryotes



Prokaryotes such as
bacteria divide into 2
identical cells by the
process of binary
fission
Single chromosome
makes a copy of itself
Cell wall forms between
the chromosomes
dividing the cell
Parent
cell
Chromosome
doubles
Cell splits
2 identical daughter cells
18
Phases of the Cell Cycle
•
•
•
Interphase
– G1 - primary growth
– S - genome replicated
(DNA replication)
– G2 - secondary growth
M - mitosis
C - cytokinesis
19
Phases of the Cell Cycle
20
Interphase
•
•
G1 - Cells undergo majority of growth
S - Each chromosome replicates
(synthesizes) to produce sister
chromatids (DNA replication)
–
–
•
Attached at centromere
Contains attachment site (kinetochore)
G2 - Chromosomes condense - Assemble
machinery for division such as
centrioles
21
Interphase - G1 Stage
1st growth stage after cell division
 Cells mature by making more
cytoplasm & organelles
 Cell carries on its normal
metabolic activities

22
Interphase – S Stage


Synthesis stage
DNA is copied or replicated
Two
identical
copies of
DNA
Original DNA
23
Interphase – G2 Stage
2nd Growth Stage
 Occurs after DNA has been copied
 All cell structures needed for division are
made (e.g. centrioles)
 Both organelles & proteins are
synthesized

24
DNA Copied
Cells Mature
Cells prepare for
Division
Daughter
Cells
Cell Divides into Identical
cells
25
25
Mitosis



Some haploid & diploid cells divide by mitosis.
Each new cell receives one copy of every chromosome
that was present in the original cell.
Produces 2 new cells that are both genetically identical to
the original cell.
DNA duplication
during interphase
Mitosis
Diploid Cell
26
Mitosis





Division of the
nucleus
Also called
karyokinesis
Only occurs in
eukaryotes
four stages
Doesn’t occur in
some cells such as
brain cells
27
Four Mitotic Stages
Prophase
 Metaphase
 Anaphase
 Telophase

28
28
Early Prophase


Chromatin in nucleus condenses to form
visible chromosomes
Mitotic spindle forms from fibers in
cytoskeleton or centrioles (animal)
Nucleolus
Chromosomes
Cytoplasm
Nuclear Membrane
29
Late Prophase




Nuclear membrane & nucleolus are broken
down
Chromosomes continue condensing & are
clearly visible
Spindle fibers called kinetochores attach to
the centromere of each chromosome
Spindle finishes forming between the poles
of the cell
30
Late Prophase
Chromosomes
Nucleus & Nucleolus have disintegrated
31
Spindle Fiber attached to
Chromosome
Kinetochore Fiber
Chromosome
32
Review of Prophase
33
Spindle Fibers




The mitotic spindle form from the
microtubules in plants and centrioles in
animal cells
Polar fibers extend from one pole of the cell
to the opposite pole
Kinetochore fibers extend from the pole to
the centromere of the chromosome to which
they attach
Asters are short fibers radiating from
centrioles
34
The Spindle
35
35
Metaphase


Chromosomes, attached to the kinetochore fibers,
move to the center of the cell
Chromosomes are now lined up at the equator
Equator of Cell
Pole of the
Cell
36
Metaphase
Asters at the
poles
Spindle
Fibers
Chromosomes
lined at the
Equator
37
Metaphase
Aster
Chromosomes at Equator
38
Metaphase
39
Anaphase


Occurs rapidly
Sister chromatids
are pulled apart to
opposite poles of
the cell by
kinetochore fibers
40
Anaphase
Sister
Chromatids
being
separated
41
Anaphase
42
Telophase

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
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Sister chromatids at opposite poles
Spindle disassembles
Nuclear envelope forms around each set of
sister chromatids
Nucleolus reappears
CYTOKINESIS occurs
Chromosomes reappear as chromatin
43
Comparison of Anaphase & Telophase
44
44
Mitosis in a plant cell
Chromatine
Nucleus
Nucleolus condensing
1 Prophase.
The chromatin
is condensing.
The nucleolus is
beginning to
disappear.
Although not
yet visible
in the micrograph,
the mitotic spindle is
staring to from.
Chromosome
Metaphase. The
2 Prometaphase.
3
4
spindle is complete,
We now see discrete
and the chromosomes,
chromosomes; each
attached to microtubules
consists of two
at their kinetochores,
identical sister
are all at the metaphase
chromatids. Later
plate.
in prometaphase, the
nuclear envelop will
fragment.
5
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends
of cell as their
kinetochore
microtubles shorten.
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will
divided the cytoplasm
in two, is growing
toward the perimeter
of the parent cell.
45
Cytokinesis
Means division of the cytoplasm
 Division of cell into two, identical halves
called daughter cells
 In plant cells, cell plate forms at the
equator to divide cell
 In animal cells, cleavage furrow forms to
split cell

46
Cytokinesis In Animal And
Plant Cells
Cleavage furrow
Contractile ring of
microfilaments
100 µm
Vesicles
forming
cell plate
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (SEM)
47
Cytokinesis
Cleavage furrow in
animal cell
Cell plate in animal
cell
48
48
Daughter Cells of Mitosis
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

Have the same number of chromosomes as
each other and as the parent cell from which
they were formed
Identical to each other, but smaller than
parent cell
Must grow in size to become mature cells
(G1 of Interphase)
49
Identical Daughter Cells
2
Chromosome number the same, but cells smaller than
parent cell
50
Mitotic Division of an Animal Cell
G2 OF INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Chromatin
(duplicated)
Nuclear
Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
Chromosome, consisting
of two sister chromatids
PROMETAPHASE
Fragments
of nuclear
envelope
Kinetochore
Nonkinetochore
microtubules
Kinetochore
microtubule
51
Mitotic Division of an Animal Cell
METAPHASE
ANAPHASE
Metaphase
plate
Spindle
Centrosome at Daughter
one spindle pole chromosomes
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
52
G2 of Interphase
 A nuclear envelope bounds
the
nucleus.
 The nucleus contains one or
more
nucleoli (singular, nucleolus).
 Two centrosomes have
formed by
replication of a single centrosome.
 In animal cells, each
centrosome
features two centrioles.
 Chromosomes, duplicated
during S
phase, cannot be
seen individually
because they have not yet condensed.
The light micrographs show dividing lung
cells from a newt, which has 22
hromosomes in its somatic cells
(chromosomes appear blue, microtubules
green, intermediate filaments red). For
simplicity, the drawings show only four
chromosomes.
G2 OF INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Chromatin
(duplicated)
Nuclear
Plasma
envelope membrane
53
Prophase
• The chromatin fibers become
more
tightly coiled, condensing into discrete
chromosomes observable with a light
microscope.
• The nucleoli disappear.
• Each duplicated chromosome appears
as two identical sister chromatids joined
together.
• The mitotic spindle begins to form.
It is composed of the centrosomes and
the microtubules that extend from them.
The radial arrays of
shorter
microtubules that extend
from the
centrosomes are called asters (“stars”).
• The centrosomes move away from each
other, apparently propelled
by the
lengthening microtubules between them.
PROPHASE
Early mitotic Aster
Centromere
spindle
Chromosome, consisting
of two sister chromatids
54
Metaphase
• Metaphase is the longest stage of
mitosis, lasting about 20 minutes.
• The centrosomes are now at
opposite ends of the cell.
•The chromosomes convene on the
metaphase plate, an imaginary
plane that is equidistant between
the spindle’s two poles. The
chromosomes’ centromeres lie on
the metaphase plate.
• For each chromosome, the
kinetochores of the sister
chromatids are attached to
kinetochore microtubules coming
from opposite poles.
• The entire apparatus of
microtubules is called the spindle
because of its shape.
METAPHASE
Metaphase
plate
Spindle
Centrosome at
one spindle pole
55
The Mitotic Spindle
•
•
•
•
•
The spindle includes the centrosomes, the spindle
microtubules, and the asters
The apparatus of microtubules controls
chromosome movement during mitosis
The centrosome replicates, forming two
centrosomes that migrate to opposite ends of the
cell
Assembly of spindle microtubules begins in the
centrosome, the microtubule organizing center
An aster (a radial array of short microtubules)
extends from each centrosome
56
The Mitotic Spindle
•
•
Some spindle microtubules attach to the kinetochores of
chromosomes and move the chromosomes to the metaphase
plate
In anaphase, sister chromatids separate and move along the
kinetochore microtubules toward opposite ends of the cell
Aster
Microtubules
Sister
chromatids
Chromosomes
Centrosome
Metaphase
plate
Kinetochores
Centrosome
1 µm
Overlapping
nonkinetochore
microtubules
Kinetochore
microtubules
0.5 µm
57
Anaphase
 Anaphase is the shortest stage of mitosis,
lasting only a few minutes.
 Anaphase begins when the two sister
chromatids of each pair suddenly part.
Each chromatid thus becomes a fullfledged chromosome.
 The two liberated chromosomes begin
moving toward opposite ends of the cell, as
their kinetochore microtubules
shorten.
Because these microtubules are attached at the
centromere region, the chromosomes move
centromere first (at about 1 µm/min).
 The cell elongates as the non kinetochore
microtubules lengthen.
 By the end of anaphase, the two ends of
the cell have equivalent—and complete—
collections of chromosomes.
ANAPHASE
Daughter
chromosomes
58
Telophase
• Two daughter nuclei begin to
form in the cell.
• Nuclear envelopes arise from
the fragments of the parent
cell’s nuclear envelope and
other portions of the
endomembrane system.
• The chromosomes become
less condensed.
• Mitosis, the division of one
nucleus into two genetically
identical nuclei, is now
complete.
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nucleolus
forming
Nuclear
envelope
forming
59
Meiosis
Formation of Gametes
(Eggs & Sperm)
60
Meiosis
1. Reduction in amount of genetic material in the daughter
cell
2. A type of cell division that results in four daughter cells
each with half number of chromosome of the parent
cell, as in the production of gametes and plant spores
3. The process by which the nucleus divides in all sexually
reproducing organisms during the production of spores
and gametes
4. The process by which the cell divides producing
daughter cell that have a single set of chromosomes and
are called haploid as opposed to diploid cells with two
sets of chromosome
61
Facts About Meiosis


Preceded by interphase which includes
chromosome replication
Two meiotic divisions:
1. Meiosis I
2. Meiosis II


(Reduction- division)
Original cell is diploid (2n)
Four daughter cells produced that are
monoploid (1 n)
62
Facts About Meiosis
•
•
•
•
Only diploid cells can divide by meiosis.
Prior to meiosis I, DNA replication occurs.
During meiosis, there will be two nuclear
divisions, and the result will be four haploid
nuclei.
No replication of DNA occurs between
meiosis I and meiosis II.
63
Facts About Meiosis
Daughter cells contain half the number
of chromosomes as the original cell
 Produces gametes (eggs & sperm)
 Occurs in the testes in males
(Spermatogenesis)
 Occurs in the ovaries in females
(Oogenesis)

64
Meiosis


It is the fundamental basis of sexual
reproduction
Two haploid (1n) gametes are brought
together through fertilization to form a
diploid (2n) zygote
65
Fertilization
2n = 6
1n =3
“Putting it all together”
66
Stages of Meiosis
Begins with Interphase
Chromosomes replicate
Meiosis I
Meiosis II
•
Prophase I
•
Prophase II
•
Metaphase I
•
Metaphase II
•
Anaphase I
•
Anaphase II
•
Telophase I
•
Telophase II
67
Replication of Chromosomes




Replication is the
process of
duplicating a
chromosome
Occurs prior to
division
Replicated copies
are called sister
chromatids
Held together at
centromere
Occurs in
Interphase
68
A Replicated Chromosome
Gene X
Homologs
(same genes,
different alleles)
Sister
Chromatids
(same genes,
same alleles)
Homologs separate in meiosis I and therefore
different alleles separate.
69
Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by
half
Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right
number!
70
Meiosis:
Two Part Cell Division
Sister
chromatids
separate
Homologs
separate
Meiosis
I
Meiosis
II
Diploid
Haploid
Haploid
71
Meiosis I:
Reduction Division
Spindle
fibers
Nucleus
Early Prophase I
(Chromosome
number doubled)
Late
Prophase I
Nuclear
envelope
Metaphase I
Anaphase I
Telophase I
72
Prophase I
Early prophase
Homolog’s pair.
 Crossing over
occurs.
Late prophase
Chromosomes condense.
Spindle forms.
Nuclear envelope fragments.
73
Tetrads Form
in Prophase I
Homologous chromosomes
(each with sister chromatids)
Join to form a
TETRAD
Called Synapsis
74
Crossing-Over



Homologous
chromosomes in a
tetrad cross over
each other
Pieces of
chromosomes or
genes are
exchanged
Produces Genetic
recombination in
the offspring
75
Homologous Chromosomes
During Crossing-Over
76
Crossing-Over
Crossing-over multiplies the already huge number of
different gamete types produced by independent
assortment
77
Metaphase I
Homologous pairs of
chromosomes align
along the equator of
the cell
78
Anaphase I
Homolog’s separate and move
to opposite poles.
Sister chromatid’s remain
attached at their centromers.
79
Telophase I
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
80
Meiosis II
Gene X
Only one homolog of each
chromosome is present in the
cell.
Sister chromatids carry
identical genetic
information.
Meiosis II produces gametes with one copy of
each chromosome and thus one copy of each
gene.
81
Meiosis II
Prophase II
Metaphase II
Telophase II
Anaphase II
4 Identical
haploid cells
82
Prophase II
Nuclear envelope
fragments.
Spindle forms.
83
Metaphase II
Chromosomes align
along equator of cell.
84
Anaphase II
Equator
Pole
Sister chromatids
separate and move to
opposite poles.
85
Telophase II
Nuclear envelope
assembles.
Chromosomes
decondense.
Spindle disappears.
Cytokinesis divides cell
into two.
86
Results of Meiosis
Gametes (egg & sperm) form
Four haploid cells with one
copy of each chromosome
One allele of each gene
Different combinations of
alleles for different genes along
the chromosome
87
Gametogenesis
Oogenesis or Spermatogenesis
88
Spermatogenesis




Occurs in the testes
Two divisions
produce 4 spermatids
Spermatids mature
into sperm
Men produce about
250,000,000 sperm
per day
89
Spermatogenesis in the
Testes
Spermatid
90
91
91
Oogenesis





Occurs in the ovaries
Two divisions produce 3 polar bodies that
die and 1 egg
Polar bodies die because of unequal division
of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte matures into
an ovum (egg) every 28 days
92
Oogenesis in the Ovaries
93
93
Oogenesis
First polar body
may divide
(haploid)
a
Mitosis
Oogonium
(diploid)
A
X
X
Primary
oocyte
(diploid)
X
a
X
a
a
X
Polar
bodies
die
Meiosis I Meiosis II
(if fertilization
A
occurs)
X
A
X
Secondary
oocyte
(haploid)
Ovum (egg) Mature
A
egg
X
Second
polar body
(haploid)
94
Mitosis & Meiosis
Mitosis
•
•
•
•
Functions
– Asexual
reproduction
– Growth, repair
Occurs throughout
plant
Produces clones
Diploid parents and
offspring
Meiosis
•
•
•
•
Function
– Sexual reproduction
Occurs only in cells
that give rise to sperm
and eggs
Produces variable
offspring
Diploid parents,
haploid offspring
95
Mitosis & Meiosis
Mitosis
Meiosis
Number of divisions
1
2
Number of daughter cells
2
4
Yes
No
Same as parent
Half of parent
Where
Somatic cells
Germ cells
When
Throughout life
At sexual maturity
Role
Growth and
repair
Sexual reproduction
Genetically identical?
Chromosome number
96
Mitosis and Meiosis
•
•
Mitosis
–
Two diploid cells produced
–
Each identical to parent
Meiosis
–
Four haploid cells produced
–
Differ from parent and one another
97