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Cell Growth & Division
What problems does growth
pose for cells?
DO NOW
Why do cells need to be small?
Why do cells need to be small?
– Trouble moving enough nutrients and
wastes across the cell membrane
– Organization
– The larger a cell becomes, the more
demands on its DNA
Purpose of cell division?
Chromosomes
Chromosome number is unique to
every species
•
•
•
•
Humans: 46 chr.
Chimpanzees: 48 chr.
Yeast: 32 chr.
Adders-Tongue Fern: 1440 chr.!
Moral:
Quality of the Genetic
Material and NOT the
Quantity
give an organism
complexity
23
Chromosomes
• Humans have 46 chromosomes in every cell
• During S-phase of the cell cycle, all 46 are copied
• When the cell splits in half, each new cell has the
exact same chromosome # as before
MITOSIS
Parent
Cell
Daughter
Cells
Checkpoints
G1 Checkpoint:
-
Cell size
-
DNA can be replicated
G2 Checkpoint
-
Cell size
-
DNA intact
-
DNA duplicated
M checkpoint
- Chromosomes are
properly attached to the
spindle fibers.
What happens if the cell cannot
pass through the checkpoint?
1. Repair the damage
OR
2. Self-destruct
APOPTOSIS
(Programmed Cell
Death)
I. Interphase:
90% of the time!
1. Gap 1
2. Synthesis
3. Gap 2
cell grows, doubles organelles
Duplication of the DNA
cell grows
MITOSIS : NUCLEAR DIVISION
During Mitosis the movement of the chromosomes (DNA) are
guided by spindle fibers which are long proteins that grow
from the centrioles (in animal cells) or the membrane (in
plant cells).
Steps of Mitosis: (PMAT)
Prophase
Metaphase
Anaphase
Telophase
http://www.goldiesroom.org/Note%20Packets/14%20Mitosis%20and%20Asexual/00%20Mito
sis--WHOLE.htm
1. Prophase• Chromatin fibers condense
• Nuclear membrane breaks down
• Spindle of microtubules forms from centrioles
[animals only]
2. Metaphase- “middle”
•
•
Spindle fibers from centrioles attach to
centromeres
Spindles move Chromosomes to line up in the
middle
Centriole
Spindle
3.
Anaphase: “away phase”, form “A’s”
•
•
•
•
Spindle fibers contract
Pull sister chromatids apart
Chromosomes move towards opposite ends
Each side has own copy of DNA
Individual
chromosomes
4. Telophase- “end phase”
•
•
•
Nuclear membranes reform at each pole
Chromosomes unwind
Spindle disappears
Cytokinesis
(NOT a phase of Mitosis)
During cytokinesis, the cytoplasm cuts
in half
Each daughter cell has an identical set
of duplicate chromosomes
Cytokinesis in Plants
In plants, a structure known as the cell plate
forms midway between the divided nuclei.
Cytokinesis in Animals
Animal cells contract an
actin fiber across
middle of cell and “pinch”
into 2 new cells. - called
a “cleavage furrow”.
Cancer Cells…
- Do not stop dividing when they contact other
cells
- Do not respond to signal and divide
uncontrollably
- Don’t stop at checkpoints and do not do
apoptosis
- Form masses of cells called tumors
- Metastasis: tumor cells break loose and
spread in body
Contact Inhibition
- Normal cells will reproduce until they
contact other cells.
- When this happens, they stop growing.
How are cancer cells different from other cells?
Tumors - mass of cancer cells.
The cells attract new blood vessel growth
(this is called angiogenesis)
Causes of Cancer/Carcinogens
/ Random Mutations
/ Genetics
/Chemicals- asbestos, cigarettes,
formaldehyde, pesticides, nitrates
/ Radiation
/ Certain viruses (HPV)
/ Poor Diet/ Obesity
Prevention of Cancer
/ Genetic screening BRCA 1 and BRCA 2
/ Do not smoke
/ limit alcohol consumption
/ Maintain a proper diet
/ exercise
/ prevent sunburns
/ Get Proper health screenings
Mutations typically happen in
two types of genes
1. Proto-oncogenes are normal genes
that regulate cell growth
Oncogenes are mutated
proto-oncogenes
2. Tumor suppressor genes – genes that
stop the cell cycle or promote apoptosis
ex. p53 gene
p53 gene,
Tumor suppressor gene "guardian
of the genome", usually functions to
properly control the cell cycle
p53 is mutated in over 50% of all
human cancers.
Biopsy- way to
diagnose
cancer by
surgically
removing piece
of tissue and
examining it
Staging
- Describes the severity of a person’s cancer
- Aids in planning the treatment
MEIOSIS
Sperm and egg.
Meiosis
- the production of haploid cells with unpaired
chromosomes - word means "to diminish".
-process creates
gametes (sperm
and eggs), cells that
are haploid (1N)
-gametes combine
to create a zygote
which is diploid (2N)
Meiosis is actually
TWO divisions, this
results in FOUR
daughter cells, each
with HALF the
number of
chromosomes.
These cells are
HAPLOID!
Homologous Chromosomes
- each chromosome has a match,
called a homolog.
This is why normal organisms
always have an even number
of chromosomes.
Chromosomes are numbered and
paired according to their size.
Karyotype showing
homologous pairs.
Why Meiosis increases Genetic Variation
During Prophase I homologous
chromosomes pair
up and exchange
DNA. -
this is called
CROSSING-OVER
During metaphase, chromosomes line up in PAIRS, but they
line up randomly. This picture shows all the different
possible arrangements for an organism with 6
chromosomes.
This is called INDEPENDENT ASSORTMENT
Fertilization = combining the genes of two different
parents.
When gametes combine, offspring show variation due to
independent assortment and crossing over
The Phases of Meiosis
Similar in plants and animals.
Plant cells lack centrioles.
Meiosis creates gametes
(sperm and eggs)
Meiosis ensures variability in
offspring
Gametes combine to create a
zygote which is diploid (2N) process of sexual reproduction
Figure 10.9a
During OOGENESIS, cytoplasm divides unevenly during each cytokinesis,
resulting in only ONE viable egg cell.
3 small polar bodies are formed
1 large OOCYTE has potential
to be fertilized
Key points of Meiosis
●The process results in 4 daughter cells
●Daughter cells are haploid (N)
●Daughter cells have unique combinations of
chromosomes
Check for understanding
1. What phase directly follows metaphase I?
anaphase I
2. How many cells are present at the end of meiosis I ? 2
3. A cell has a diploid number of 60, what is the organism's
haploid number?
30
4. Meiosis occurs in what type of cells? gametes
5. In what phase do homologous chromosomes pair up and
crossing-over can occur?
prophase
1
6. In what phase do the CHROMATIDS separate?
anaphase 2
Pg 180
Which of these pictures is metaphase I of
MEIOSIS and which is metaphase of MITOSIS?
Mitosis
Meiosis
Mitosis Videos
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__mitosi
s_and_cytokinesis.html http://www.youtube.com/watch?v=VlN7K19QB0 http://www.cellsalive.com/mitosis.htm http://www.youtube.
com/watch?v=lf9rcqifx34å
Twilight DOES IT TOO!