Transcript Cell Division - Effingham County Schools

Anatomy and Physiology
Cell Reproduction
The Cell Cycle: Mitosis
The Cell Cycle
• The series of
changes that a
cell undergoes
from the time
it forms until
the time it
divides.
Interphase
Period between cell divisions when
a cell is carrying on its normal
functions and is preparing for
division.
• Stages of Interphase
• G1 - Growth phase - cells grow and develop,
rapid growth and protein synthesis.
• S - Synthesis phase - DNA replication
occurs.
• G2 - Growth phase - centrioles replicate,
cell prepares for cell division.
Mitosis
• Division of a
somatic cell to form
two genetically
identical nuclei or
daughter cells.
• P.M.A.T
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Mitosis
• Somatic Cells - body cells, chromosome
number is constant.
• Chromosomes exist in pairs.
– Ex. We have 23 pairs of chromosomes or 46
chromosomes.
• Called diploid or 2N (two homologous copies of
a chromosome)
• Each pair of chromosomes carries the genetic
information for the same trait - Homologous.
Chromosome Structure
• Sister Chromatids
– Duplicated
chromosome made in
S phase of
interphase.
• Centromere
– Holds sister
chromatids together.
Chromatin
All the DNA/proteins in nucleus …
condenses to form chromosomes
during Mitosis
Chromatid
Sister chromatid
Chromosomes
Condensed
chromatin .. Either 2
sister chromatids or
1 chromatid
Nucleus
Sister chromatid
4 Stages of Mitosis: Prophase
– Chromatin in the
–
–
–
–
nucleus condenses to
form visible
chromosomes.
Nuclear membrane
breaks down.
Nucleolus disappears.
Centrioles move to
opposite sides of the
cell.
Microtubules form
spindle fibers
attached to
centrioles.
4 Stages of Mitosis:
Metaphase
Chromosomes
align in the
center of the
cells and attach
to the spindle
fibers by their
centromeres.
4 Stages of Mitosis: Anaphase
• Centromeres
separate- sister
chromatids move to
opposite ends (poles)
of the cell.
• The individual sister
chromatids are now
call individual
chromosomes.
4 Stages of Mitosis:
Telophase
– Like prophase in
reverse.
– Chromosomes uncoil.
– Nuclear membrane
reforms around
chromosome set.
– Nucleoli become
visible inside nucleus
again.
– Spindle fibers break
down.
Cytokinesis: Cytoplasmic
Division
• Considered a
separate stage.
• Cell membrane
pinches in on
itself until 2
daughter cells
are formed.
Cytokinesis
• Regulation
• Internal and external factors regulate cell
division.
• Cancer is the uncontrolled growth and division of cells.
• Cancer cells can kill an organism by crowding out normal cells,
resulting in the loss of
tissue function.
Cancer
cancer cell
normal cell
bloodstream
metastasize
Benign
Malignant
• Causes of Cancer
• Internal Factors
– Inheritance
– Mutations
Skin
Cancer
• External Factors
» Carcinogens are substances that are known to
produce and promote the
development of cancer.
– Radiation
– Chemical
– Viruses
Mitosis
Cell Differentiation
• The process by
which cells develop
different structures
and specialized
functions.
• Controlled by the
activation of certain
genes.
Stem Cells
 A precursor cell that can be triggered
by genes to become any type of cell.
Meiosis
Why does it take place?
•Forming of gametes which are haploid cells
Where does it take place?
•Reproductive organs – Male = testes
Female = ovaries
46
23
46
+
haploid
23
haploid
fertilization
46
Meiosis - Formation of Gametes
• Meiosis only occurs
during the
production of
gametes.
• After fertilization,
the diploid zygote
divides by mitosis
producing a
multicellular,
diploid organism.
Meiosis
• Meiosis reduces the chromosome number
from diploid to haploid.
• Occurs in two divisions, called meiosis I and
meiosis II.
• Divisions result in 4 daughter cells, each with
half the number of chromosomes as the
parent. (Haploid = n)
• Meiosis 1 separates the homologous
chromosomes (2 copies of each chromosome-1
from mom & 1 from dad) and Meiosis 2
separates sister chromatids.
Karyotype of a Female
Homologous chromosomes
Two Meiotic Divisions
Meiosis I
Meiosis II
Comparing Mitosis and Meiosis
Formation of Sperm vs. Formation of Eggs
4 haploid gametes … 4
sperm
Process = Spermatogenesis
4 haploid gametes …
1 Ovum (egg) & 3 Polar Bodies
Process = Oogenesis