Transcript Document 7930695

Mitosis
How Cells Reproduce
Types of Cells
• The body contains two different types of
cells
– Somatic cells
• Reproduce by mitosis (asexual reproduction)
• They are diploid, that is they contain two complete
sets of genetic information, (one from each parent)
– Gametes
• Reproduce by meiosis (sexual reproduction)
• They are haploid. Contain only on set of genetic
information.
Mitosis
• Aged cell transforms itself into twin youthfu
cells
• Happens millions of times every second in
the human body.
• It gradually replaces every cell in your
body except muscle and nerve cells
• In the body, what cells do you think
replace themselves the fastest?
The Cell Cycle
• The life of a cell can
be divided into
recurring different
time periods called
the cell cycle.
• Two main parts to the
cell cycle.
– Interphase
– mitosis
Fig. 9.3, p. 151
Interphase
•
The first part of
interphase is devided
into 4 different parts
1.
2.
3.
4.
G1
S
G2
Cytokinesis or the
division of the
cytoplasm
Most cells spend most their
time (90%) in interphase
Fig. 9.3, p. 151
Fig. 9.3, p. 151
centromere
one chromatid
its sister chromatid
one chromosome
(in duplicated state)
in-text, p. 163
Mitosis
• The division of the nucleus is divided into
four distinct phases
• Prophase
• Metaphase
• Anaphase
• Telephase
Prophase
pair of
centrioles
microtubules
• Chromosomes start condensing
• The spindle starts forming
kinetochores
– Centroles start to move to opposite ends of the cells
– Microtubules extend out from the centrioles to the kinetochores
on each sister chromotid
• Nuclear envelope begins to break apart
CELL AT INTERPHASE
EARLY PROPHASE
cell
LATE PROPHASE
PROMETAPHASE
chromosomes
nucleus
microtubules
pair of
centrioles
plasma
membrane
nuclear
envelope
Fig. 9.5a, p. 152
Metaphase
• Spindle fibers interact
to orient chromatids
and aligne them at
the cell’s equator,
halfway between the
poles.
Anaphase
• The microtubules that
are attached to the
kinetochores begin to
shorten and pull the
sister chromotids
apart.
• One half of each
sister chromotide
goes to each side of
the cell
Telophase
• Telophase is the
opposite of prophase
– Nuclear envelope is
reformed
– Microtubules are
wound up in the
centrioles
– Chromosomes unwind
into chromotine
Cytokinesis
(The division of the cytoplasm)
• Contractile
microfilaments at the
cleavage furrow pull
the plasma
membrane inward.
• The membranes
come together and
pinch off to form new
daughter cells
Questions
• How many DNA molecules are present in a
duplicated chromosome?
• What is being separated in anaphase?
• What type of cells undergo mitosis?
• What is the chromosome number at G1? What
is the chromosome number after cytokinesis?
METAPHASE
ANAPHASE
TELOPHASE
INTERPHASE
Fig. 9.5b, p. 153
Meiosis
The Making of gametes
Meiosis
• Meiosis can be broken up into two different
parts: Meiosis I and Meiosis II
• In meiosis the nucleus devides 2 times, once in
meiosis I and again in meiosis II
• Meiosis I is broken up into four parts
– Prophase I, Metaphase I, Anaphase I and telophase I
• Meiosis II also has four different stages.
– Prophase I, Metaphase I, Anaphase I and telophase I
Prophase I
• The exact same steps that occur in
prophase of mitosis occur here.
• There are additional steps
– Synapsis: Homologous chromosomes come
together.
– Crossing over takes place
Homologous chromosomes
• Homologous chromosomes are
chromosomes that code for the same
genes
• We inherit one homolog from each parent
• There are 23 pairs of homologous
chromosomes in human somatic cells.
MEIOSIS I
PROPHASE I
newly
forming
microtubules
in the
cytoplasm
Homologous
Chomosomes come
together in a process
called synapsis
Fig. 10.4a p. 164
Crossing over
• During synapsis homologous chromosomes
exchange segments of DNA in a process called
Crossing over
Meiosis I
• In Meiosis I the cell is separating
homologous chromosomes.
• In Meiosis II the cell is like mitosis in that
the cell is separating sister chromotids
MEIOSIS I is separating homologous chromosomes
plasma
membrane
newly
forming
microtubules
in the
cytoplasm
PROPHASE I
spindle
equator
(midway
between the
two poles)
one pair of
homologous
chromosomes
METAPHASE I
ANAPHASE I
TELOPHASE I
Fig. 10.4a p. 164
MEIOSIS II
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
Fig. 10.4b p. 165