Post on 07-Jul-2015
Mitosis
Why do cells need to divide?
Recap…
Cell theory…
Cells are the basic structural unit of life
Cells are the functional units of life
Cells come from pre-existing cells
Overview
Why do cells need to divide?
Repair, growth, development
Types of reproduction
Sexual
Genetically different
2 parents
Takes time to develop, better chance of survival
asexual
Genetically identical
One parent
Many offspring very quickly
DNA
Blueprint of life, nucleic acid
Chromatin
Granular genetic material, spread out in
nucleus of non-dividing cells
Chromosomes
Condensed genetic material, in dividing cells
Sister chromatids
Identical copies of Chromosomes joined by
a centromere (“centro-” middle)
Humans
46 chromosomes
46 sister chromatids
One from your mom, one from your dad
Cell Cycle: Life of a Cell
Cell Cycle
Interphase
90 % of cell’s life, non dividing
G1 phase
Grows, makes organelles
S phase
DNA Synthesis…DNA replicates
G2 phase
Cell prepares to divide, makes sure it has all important
organelles for division
M phase
When the cytoplasm and nucleus of the cell
divides
Cell Cycle
There are check points in G1, S, and G2
Make sure cell is ready to move onto the
next phase (has all necessary organelles,
copied DNA, etc.)
Once the cell has past the G1
checkpoint, it will complete the cell cycle
Some cells stay in the G1 phase all their
life (muscle cell, brain cells)
Regulators of Cell Cycle
Cyclins
Protein that regulates the timing of the cell
cycle in eukaryotic cells
Levels of cyclins rise and fall throughout the
cell cycle
Cyclin-dependent Kinases (cdks)
Enzymes that are activated when they bind
with cyclin and they make the cell cycle
continue
Regulators
Internal
Factors within the cell that control cell cycle
Cyclin and CDKs
Allow cell cycle to proceed only when certain processes
have occurred
Replication of chromosomes
Chromosome Attachment to spindle before anaphase
External
Factors Outside the cell
Growth factorsmolecules that bind to cell surface that
signal cell to divide
Similar cells have molecules that have opposite effect so
that when it becomes to crowded, cells stop dividing
M-phase
Consists of mitosis and
cytokinesis
Mitosis
Process by which the
nucleus of a cell divides
One parent cell makes two
identical daughter cells
This is how organisms
repair tissue and grow and
develop
Cytokinesis-division of the
cytoplasm
Depending on cell type…
Mitosis can take a few minutes or a few
days
Muscle cells (non-dividing)
Nerve cells (non-dividing)
Skin cells (divide all the time)
Digestive Tract cells (divide all the time)
Life Span of Some Human
Cells
Cell type Life span Cell division
Lining of esophagus 2-3 days Can divide
Lining of small intestine 1-2 days Can divide
Lining of the large
intestine
6 days Can divide
Red blood cells Less than 120 days Cannot divide
White blood cells 10 hours to decades Many do not divide
Smooth muscle Long-lived Can divide
Cardiac (heart) muscle Long-lived Cannot divide
Skeletal muscle Long-lived Cannot divide
Neurons (nerve) cells Long-lived Most do not divide
Prophase
50-60% of time
Chromosomes become visible
Centrioles develop in cytoplasm near nuclear
envelope
Centrioles separate and migrate to opposite ends
of nuc. Env.
Centrosome
Region where Centrioles are found
Organize the “spindle”
Fan like microtubule structure that helps separate
chromosomes
Plants do NOT have Centrioles
End of prophase
Chromosomes coil together tightly
Nucleolus disappears
Nuclear envelope breaks down
Metaphase
Few minutes
Chromosomes line up in middle (M in
metaphase MIDDLE)
Microtubules connect centromere of each
chromosome to the 2 poles of spindle
Anaphase
Centromeres joining sister chromatids
separate and become individual
chromosomes
They are dragged by fibers to opposite
poles
Ends when chromosomes stop moving
Telophase
Opposite of prophase
Condensed chromosomes disperse into
tangle of material
Nuclear envelope reforms
Spindle breaks apart
Nucleolus becomes visible
At the end 2 identical nuclei in one cell
Cytokinesis
Happens at the same time as Telophase
Division of cytoplasm
Animal Cells
Cell membrane drawn inward until it pinches
off and forms 2 id daughter cells
Plant Cells
Cell plate forms between nuclei
Cell Plate develops into separate membrane
Cell wall appears
Regulators of Cell Cycle
Cyclins
Protein that regulates the timing of the cell
cycle in eukaryotic cells
Levels of cyclins rise and fall throughout the
cell cycle
Cyclin-dependent Kinases (cdks)
Enzymes that are activated when they bind
with cyclin and they make the cell cycle
continue
Regulators
Internal
Factors within the cell that control cell cycle
Cyclin and CDKs
Allow cell cycle to proceed only when certain processes
have occurred
Replication of chromosomes
Chromosome Attachment to spindle before anaphase
External
Factors Outside the cell
Growth factorsmolecules that bind to cell surface that
signal cell to divide
Similar cells have molecules that have opposite effect so
that when it becomes to crowded, cells stop dividing
MEIOSIS
Gregor
Mendel
1822
Austrian monk
University of
Vienna
In charge of
the Garden
What Gregor Mendel
Knew…
Each organism must inherit a single copy of every gene from each of its “parents”
Each of the organisms gametes must contain just one set genes
When gametes are formed, there must be a process that separates the 2 sets of genes so each gamete gets one set
Karyotype
A photograph of a organism’s
chromosomes, arranged according to
size
Chromosome Number
Homologous chromosomes
Chromosome that has a corresponding
chromosome from the opposite-sex parent
Fruit fly has 8 chromosomes
4 from mom
4 from dad
Diploid
Di= two sets
Cell that contains both sets of homologus chromosomes Cell contains
2 complete sets of chromosome
2 complete sets of genes
Number of chrms in diploid cell represented by 2N
For Drosophilia (fruit fly) 2N=8
Mendel said: Each adult cell contains two copies of each gene
Haploid
Means “one set”
Refers to cells that contain only one set
of chromosomes
Gametes (sex cells)
Represented by N
Drosophilia fruit fly
N=4
How are
haploid (N)
gametes made
from diploid
(2N) cells?
Meiosis
Process of reduction division in which the
number of chromosomes per cell is cut in
half through the separation of
homologous chromosomes in a diploid
cell
Meiosis
2 distinct stages
Meiosis I
A diploid cell enters here
Meiosis II
At the end of this, the diploid cell that
entered meiosis has become 4 haploid cells
Meiosis I
Before meiosis 1, each chromosome is replicate
Then they divide like in mitosis
What happened in mitosis? PMAT
Tetrad STRUCTURE MADE WHEN EACH
CHROMOSOME PAIRS UP WITH ITS HOMOLOGOUS CHROMOSOME
4 CHROMATIDS IN A TETRAD
Prophase 1
Each chromosome pairs with its
homologous chromosome making a
tetrad
As they pair up in tetrads, chromosomes
exchange portions of their chromatids in
the process …. CROSSING OVER
Crossing Over
Metaphase1
Spindle fibers attach to chromosomes
Anaphase 1• The spindles pull homologous
chromosomes apart to opposite
poles/ends
Telophase 1• Nuclear membranes form and cell
separates into two new cells
Now what do we have?
2 new daughter cells
Are they identical to the parents?
No
The parent has 4 chromosomes
Each daughter cell has 4 chromosomes but they
are different because of crossing-over
Each daughter cell has a set of chromosomes
and alleles different from each other and
different from the parent diploid cell
Meiosis II
Unlike Mitosis, Neither cell goes through
a round of chromosome replication
Each cell’s chromosome has 2
chromatids
Prophase II
Meiosis I resulted in 2 “seemingly” diploid
cells
Remember they are genetically different b/c
of crossing over in prophase I
We still need to cut this number in half to
reach our goal of 4 haploid cells
Metaphase 2
Chromosomes line up in middle
Anaphase 2• Sister chromatids separate and move to
opposite poles
Telophase 2• Meiosis II results in 4 haploid (N)
daughter cells
• 4 daughter cells contain haploid number
of chromosomes, just 2 each
Gamete Formation
Male
Haploid gametes produced by meiosis are called
sperm
Female
Haploid gamete produced by meiosis is called an
egg
Cell divisions at the end of meiosis one and two
are uneven so one cell gets most of the cytoplasm
(the EGG) and the other three are called polar
bodies (don’t participate in reproduction)
Mitosis vs. Meiosis
Mitosis Results in the production of two genetically
identical DIPLOID cells
Daughter cells have sets of chromosomes identical to each other and to parent cell
MITOSIS allows body to grow and replace other cells
Asexual reproduction
Meiosis Results in four genetically different HAPLOID cells
MEIOSIS is how sexually reproducing organisms make gametes
Genes
Microscope Lab Analysis
Mitosis/Meiosis Microscope Lab Lab notebooks Title
“Cell Division Microscope Lab”
MUST sketch each stage and label the power
Label slide name
Stage of mitosis or meiosis
Power of the objective used to observe cell
Need to observe each stage of mitosis and meiosis