Download Cell unit pt 2

Cellular Reproduction
• Cellular reproduction
occurs in both Eukaryotic
and Prokaryotic cells
• Cellular reproduction in
multicellular organisms is
important for growth and
to insure the survival of
that species.
• Cellular reproduction in
unicellular organism is
only important for the
survival of that species.
• When cells reproduce
they go through a process
called cell division
Reproduction of Organisms
• Cells that divide in multicellular
organisms to produce sex cells
for sexual reproduction is
called meiosis (we’ll discuss
later).
• Unicellular organism divide
asexually to produce their
offspring
• Asexual reproduction include
- binary fission (bacteria)
- budding (yeast)
binary fission
budding
Cell Division: Mitosis & Cytokinesis
• In Eukaryotic cells, cell
division has two parts called
mitosis and cytokinesis
• Mitosis is the process by
which the nucleus of the cell
is divided into two new
nuclei, each nucleus with
same number and kinds of
chromosomes as the parent
cell.
• Cytokinesis is the process
by which the cytoplasm
divides, thus forming two
distinct cells.
Mitosis
Cytokinesis
Chromosomes
• Chromosomes are structures in the
nucleus of a cell that contain genetic
(DNA) information that is passed on
from one generation to another.
• After DNA replication the
chromosomes become visible. As
seen in the diagram to the right a
chromosome is made up of two
identical parts (Chromatids or Sister
Chromatids) Each chromatid is
attached to each other at the center
called a centromere
Chromosomes and their numbers
The parents cells of an organism
contain a certain number of
chromosomes. We called this number the
Diploid number.
 Diploid cells have two complete sets
of chromosomes, one set inherited from
each parent.The diploid is often
abbreviated as 2n.
 Daughter cells that develop from
parent cells can have a diploid number
(2n) of chromosomes or a haploid
number (n) of chromosomes
 Haploid cells have half the usual
number of chromosomes, or only one
chromosome set.
parents cells
(always diploid)
Daughter cells or
diploid
Daughter cells
haploid
Cells and their Chromosomes
• Somatic cells (all body
cells except reproductive
cells) are diploid as parent
cells and diploid as
daughter cells.
• Germ cells (reproductive
cells) are diploid as parent
cells and haploid as
Gametes (daughter sex
cells). Male gametes are
sperm, female gametes are
the egg cell.
The Cell Cycle
• The cell cycle is the period
from the beginning of one
mitosis to the beginning of the
next.
• Notice the Blue area on the
outside called interphase.
• Notice the Red area on the
outside called mitosis.
• These two areas make up the
cell cycle.
• Notice at the end of mitosis
two new cells are produced.
Interphase
• The longest period of the cell cycle.
The cell spends about 3/4 of the cell
cycle time in interphase
• Not considered part of mitosis,
sometimes call the “resting stage”, but
it is actually a period of intense
activity.
• Interphase is divided into three phases:
G1, S, G2. Each is characterized by
specific events
• G1or gap 1, growth occurs
• The S phase DNA replication occurs,
along with protein synthesis.
• G2 or gap 2, preparation for cell
division occurs
Cytoplasm
Nucleolus
Chromatin
Interphase
The S phase
Mitosis: Prophase
• The longest phase of mitosis.
• Sister Chromatids become
visible. (Notice the number of
chromatids/chromosomes is 4)
• The centrioles, separate from
each other and take position on
the opposite sides of the
nucleus.
• Centrioles form spindle fibers, a
meshlike structure made of
tubulin, a microtuble protein
helps move the chromosomes.
• The nucleolus disappear and the
nuclear membrane break down.
centriole
Sister
Chromatids
spindle fibers




nuclear
membrane
Metaphase
• The shortest phase of
mitosis.
• The sister chromatids line
up across the center
(MIDDLE) of the cell.
• Microtubles connect the
centromere of each
chromatids to the poles of
the spindle.
• Because of their starlike
arrangement around the
poles of the spindle, these
microtubules are called
asters.
asters

Centromere



Anaphase
• Begins when the centromeres
that join the sister chromatids
split.
• The sister chromatids separates
forming individual
chromosomes, the two set of
chromosomes move to opposite
poles
• Biologists are not sure what
provides the force that separates
the chromosomes.
chromosomes
Telophase
• The End or Final stage of mitosis
• The chromosomes, which have
been distinct and condensed, now
begin to uncoil into a tangle of
chromatin.
• the nuclear membrane reforms
around the chromatin, the spindle
begins to break apart and a
nucleolus becomes visible.
• Notice that the number of
chromosomes, (4) is the same as
when mitosis started.
Cytokinesis
• This is the physical
division of the cytoplasm
of eukaryotic cells into
two daughter cells after
mitosis.
daughter
• Animal cells divide
cells
when microfilaments
pull past one another,
decreasing the diameter
of the cell and creating a
cleavage furrow around
the circumference of the
cell.
cleavage
furrow
Cytokinesis con’t
• Plant cells divide by
forming a cell plate
of cellulose, which
lays down along the
membrane, dividing
the cytoplasm into
two parts and
forming a cell wall
between the
daughter cells.
cell plate
Plant Cell Mitosis
Use these
terms and
label the
phases of
mitosis and
identify the
different
structures
in the
diagrams.
prophase
metaphase
telephase
interphase
anaphase
chromosome
centriole
spindles
centromere
What is the correct order of the stages of mitosis
shown above?
F1–4–3–2
G2–4–1–3
H4–1–2–3
J4–2–1–3
Which figure shows the last stage of mitosis?
A Figure 1
B Figure 2
C Figure 3
D Figure 4
Meiosis
• Meiosis is the cell division in
• Reproduction involves the
which the number of
fusing of two gametes (n)
chromosomes is halved during the
(fertilization) to produce a
formation of gametes (haploid
zygote (2n).
cells).
• The gametes (n) are produced by
a process called meiosis which
involves two divisions.
• All cells within the body of a
sexually reproducing organism
originated from a single fertilized
egg.
• Variations of genes occur when
the exchange of chromosome
segments (crossing over) take
place during prophase 1.
Differences between Mitosis
and Meiosis
Mitosis
Meiosis
• One division only
• Two divisions
• 2 daughter cells
• 4 daughter cells
• All daughter cells contain a
haploid number (n) of
chromosomes
• Chromosomes line up in pairs
on the central plane
• All daughter cells
contain a diploid
number (2n) of
chromosomes
• Chromosomes line
up randomly on the
central plane
• Chromatids separate
• Chromosome pairs separate in
the first division followed by
the separation of the
chromatids in the second
division
Mitosis vs Meiosis
greatest number of chromosomes
• Parent Cell of Mitosis
• Parent Cell of Meiosis
somatic cells = diploid (2n)
germ cell = diploid (2n)
body cells = diploid (2n)
root cells = diploid (2n)
• Daughter Cell of Meiosis
liver cells = diploid (2n)
sex cells = haploid (n)
• Daughter Cell of Mitosis
gametes = haploid (n)
all are diploid (2n)
sperm = haploid (n)
egg (ovum) = haploid (n)
• Fertilization of sex cells
zygote = diploid (2n)
Zygote Development via Mitosis