Download cell division

CELL DIVISION
Types of Cell Division
• Mitosis – makes new body
cells (in eukaryotes)
• Binary Fission – makes new
cells (in prokaryotes)
• Meiosis – makes new sex
cells (in eukaryotes)
WHY DIVIDE?
• Why do multicellular organisms do mitosis?
– To repair or heal
– To grow and develop
– To replace cells that die
• Why do unicellular organisms do mitosis
(eukaryotes) or binary fission
(prokaryotes)?
– To reproduce asexually (cloning)
• Why do multicellular organisms for meiosis?
– To reproduce sexually
Important part of Cell Division
• Nucleus - contains genetic information
(DNA)
• Chromosomes – strands of DNA
• When a cell divides, the new cells made must
have the correct number of chromosomes.
• Most of the time, DNA looks like a lump of
spaghetti, and is called chromatin.
Cell Cycle
Cell Cycle
• Interphase
– G0 – cell at rest; is not preparing
for division
– G1 – cell gets ready for division
– S – chromosomes copy themselves
– G2 – cell checks for mistakes and
prepares for division
• Mitosis – cell divides
• Most of the time cells are not
dividing.
• Several proteins are involved
in starting division.
• Some cells can divide in as
little as 20 minutes.
• Cells typically stop dividing
when:
– Nutrient levels drop (no
food)
–They come into contact
with other cells (no room)
–Receive chemical signals
to stop.
INTERPHASE
• Cells spend most of their life in
interphase.
• Normal cell activities occur.
• To prepare for cell division, the
chromosomes make copies of
themselves.
• In other words, the DNA replicates.
• Recall, DNA polymerase… etc.
MITOSIS: CELL DIVISION
FOR EUKARYOTES
Four Stages
1.Prophase
2.Metaphase
3.Anaphase
4.Telophase
Some animations….
Cells Alive animation
McGraw animation
John Kyrk animation
PROPHASE
• Chromatin condenses and
becomes visible as
chromosomes.
• The nucleus and its various
parts disappear.
• Spindle fibers are made and
attach to the chromosomes.
• Centrioles separate and
move to opposite ends (poles)
of the cell.
• Each copy of the chromosome
is called a chromatid.
• The two chromatids are
attached at the centromere.
Chromosome
chromatids
centromere
METAPHASE
• The chromosomes line up
at the middle of the cell
(equator).
ANAPHASE
• The joined chromatids separate
and move to opposite ends of the
cell.
• In plant cells, the cell plate
begins to form.
TELOPHASE
• The chromatids arrive at the
opposite poles of the cell.
• Spindle fibers disappear.
• New nuclei form in the two new
cells.
• Cytokinesis - pinching in of cell
membrane (formation of cleavage)
in order to form two new cells
END RESULTS OF MITOSIS
• Two new “daughter” cells are made
with each containing the same
number and kinds of chromosomes
as the original (parent) cell.
• They have the same genetic code.
BINARY FISSION: CELL DIVISION
FOR PROKARYOTES (BACTERIA)
• Bacteria only have one chromosome so
they do not have to go through the
steps of mitosis and instead do binary
fission.
• The single chromosome attaches to
the cell membrane.
• The DNA replicates making 2
identical chromosomes – one for each
new cell.
• The cell elongates and
eventually separates into
2 new cells.
• Each cell gets one
chromosome.
CANCER
• Caused by uncontrollable mitosis.
• Cells either fail to stop dividing or get
signals to continue dividing.
• An increased number of cells makes a tumor.
• Tumors can be benign (non-cancerous) or
malignant (cancerous).
• Cancer cells spread (metastasis) throughout
body, unlike normal cells!
Some Causes of Cancer
•
•
•
•
•
Genetics
Radiation
Carcinogens
Old Age
Viruses
– Can mutate DNA causing some cancers
– Example: Human papillomavirus (HPV)
associated with cervical cancer in women
• Poor diets
Carcinogens
• Cancer causing agents
– Mutate DNA turning a normal cell
into a cancer cell
– Examples: cigarette smoke,
pollution
• Can cause increased amounts of
free radicals
Free Radicals
• Free radicals form when a weak bond
splits between two molecules causing
one of those molecules to lose an
electron.
• The free radical then attacks a
different molecule to steal its electron,
which causes more free radicals to
form.
• Free radicals can attack DNA!
Free Radicals and antioxidants
• Free radicals can occur in your
body naturally.
• Carcinogens can make free
radicals in the body.
• Antioxidants may battle free
radicals by bonding with them
before the free radicals can do
any harm.
Examples of Antioxidants
• Vitamins A, C, and E
• Beta carotene
• Lycopene (red pigment in
tomatoes)
Foods with High Antioxidants
• Fruits
– Ex. berries, pomegranate, grapes,
orange, plum, pineapples, kiwi,
grapefruit
• Vegetables
– Ex. cabbage, artichokes, Brussel
sprouts, spinach, red beets
• Beans/ Legumes
– Ex. soybeans, red kidney beans,
coco beans
More Foods with High
Antioxidants
• Dry fruits
– Ex. apricots, prunes, and dates
• Nuts and seeds
– Ex. pecans, walnuts, hazelnuts, sunflower
seeds
• Cereal
– Ex. barley, millet, oats, corn
Fight cancer!
• Chemotherapy (anti-cancer drugs) kills cancer
cells, but unfortunately it also damages healthy
cells. This is why people get sick when they
undergo chemotherapy.
• Radiation – kills cancer cells
• Vaccines – help prevent some cancers that are
caused by viruses (ex. Gardasil against HPV)
• Surgery – removal of cancerous tumor
• Newer, experimental treatments include gene
therapy, antiangiogenesis therapy, and
hypothermia
• Don’t smoke, eat healthy, and exercise!
MEIOSIS:
Making sex cells
CHROMOSOME NUMBER
• The number of chromosomes
varies from one kind of
organism to another.
• Humans have 46 chromosomes
& fruit flies have 8.
• Some plants have hundreds.
• Karyotype – a picture of
chromosomes that shows the
number and the size of
chromosomes that a cell has
• Amniocentesis and Chorionic
Villi Sampling– tests done on
pregnant women in order to
look at the chromosomes of
the developing baby
• Chromosomes of animal cells
are usually paired. WHY?
• Humans have 23 pairs, fruit
flies have 4 pairs.
• Haploid - the # of pairs or n
• Diploid - the total number of
chromosomes or 2n
• For humans: n=23 and 2n=46
• In diploid cells, each chromosome pair
has the same basic structure.
• Each chromosome in a pair carries a
message for the same trait, although
not necessarily the same message.
• For example, both chromosomes in a
pair have a gene for eye color, but
one may have a blue gene and the
other may have a brown gene.
• It is the combination of the two
chromosomes or genes that
determines the eye color of the
person.
SEXUAL REPRODUCTION
• Fertilization - the combination of
chromosomes (genetic
information) from two sex cells
(combining sperm and egg)
• Each sex cell gives half of the
total chromosomes.
• Sex cells are also called
gametes.
–Female sex cell = egg or
ovum
–Male sex cell = sperm
• Gametes are haploid
(half the chromosomes).
Gamete Production
• Gametes are produced in gonads.
• Eggs are made in ovaries.
– Females begin making their eggs
before they are born!
– They stop making eggs during
menopause.
• Sperm are made in testes.
– Males make sperm from
approximately puberty until death.
• After fertilization, the
developing organism is called a
zygote and is diploid.
• After fertilization the zygote
grows bigger by doing
MITOSIS.
• A zygote becomes an embryo
and later a fetus.
MEIOSIS
• Meiosis converts a diploid cell into 4
haploid gametes.
• It increases genetic diversity in the
offspring.
• Meiosis is divided into two main parts
labeled I and II.
MEIOSIS I
• PROPHASE I
– Homologous (similar)
chromosomes find their
partner (a step unique to
meiosis)
– This means the same-sized
chromosomes find each other.
• METAPHASE I
»The chromosomes
line up in the middle
of the cell with their
partners.
• ANAPHASE I
–The pairs separate and
the individual
chromosomes move to
separate poles.
• TELOPHASE I
– Each of the daughter cells is
now haploid, but each
chromosome still has two
chromatids.
MEIOSIS II
• Meiosis II is similar to
mitosis.
• However, there is no
interphase and almost no
prophase.
• METAPHASE II
–The individual chromosomes
line up in the middle of the
two new cells.
• ANAPHASE II
–The chromatids separate
and move to opposite ends
of the two cells.
• TELOPHASE II
– Both new cells complete
division making four new cells.
MEIOSIS END RESULT
• Meiosis makes 4 haploid, sex cells.
• These 4 cells are sex cells (sperm
and egg).
• Each cell has half the number of
chromosomes as the parent cell
(haploid).