Download Cell Division - Shelton School District

Cell Division
Chapter 9
 Why do you think cells in all plants and
organisms need to divide?
 To replace damaged tissue
 To increase in size
 To reproduce
Repair
• Cells are constantly repairing themselves
• If a cell can’t be repaired new ones are
produced to fill the void
Growth
• Cells are also what create our size
• As we grow our cells are constantly
reproducing
• If the reproduction rate is faster than normal
we grow
Reproduction
Asexual
• Done by somatic or
body cells
• Creates identical
daughter cells
Sexual
• Done by sex cells
• Creates genetically
different daughter cells
What do we need for cell division?
• Chromatin: a mass of DNA found in the
nucleus
What do we need for cell division?
• Chromosome: a compacted
piece of chromatin that is
used for cell division
• Sister Chromatids: A pair of
identical Chromosomes
• Centromere: The center
section where the sister
chromatids are connected
Sister chromatids
Centromere
DNA supercoil
LE 8-4
Sister chromatids
Chromosome
duplication
TEM 36,600
Centromere
Sister
chromatids
Chromosome
distribution
to
daughter
cells
How do cells divide?
• Cell Cycle: an orderly sequence of events
where cells divide
• The cell cycle consists of two major phases
– Interphase (90% of the time)
– Mitotic Phase (10% of the time)
The Cell Cycle
In humans and other mammals, cells that reproduce daily have a cell
cycle that usually lasts 10 to 20 hours.
The Cell Cycle: series of events that cells go through from
“birth” to reproduction
Interphase
• Phase where all metabolic processes and
functions happen
– Ex:
•
•
•
•
•
Cellular respiration
Protein creation
Movement
Growth
Other desired function
Interphase
• Interphase is also when the cell prepares for
cell division
– Ex:
•
•
•
•
Increases proteins
Duplicates organelles
Grows in size
Duplication of DNA
Mitotic Phase
• The division phase of the cell
• There are two main parts of M phase
– Mitosis
– Cytokinesis
Mitotic phase
• Mitosis
– The division of a cells nucleus and DNA into two
equal parts
– Creates two daughter nuclei
• Cytokinesis
– The division of the cells cytoplasm
• Together they create two identical daughter
cells
Mitosis
• Prophase:
– Sister chromatids are formed
– Formation of spindle
– Nuclear envelope breaks down
• Metaphase:
– Sister chromatids line up
– Spindle is formed and attaching to chromosomes
LE 8-6a
INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Nuclear
envelope
PROPHASE
Chromatin
Plasma
membrane
Early mitotic
spindle
PROMETAPHASE
Centrosome
Chromosome, consisting
of two sister chromatids
Centromere
Fragments
of nuclear
envelope
Kinetochore
Spindle
microtubules
Mitosis
• Anaphase:
– Separation of sister chromatids
– Spindle pulls chromosomes to either side of the
cell
• Telophase:
– Spindle breaks down
– Nuclear envelopes form (2)
– Chromosomes loosen to become chromatin
• Cytokinesis:
– Cell pulls apart to create two identical cells
LE 8-6b
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Cytokinesis in animal cells
Animal
• Formation begins with
indentation
• Cell is pulled/ pinched
until it breaks apart
Plants
• Formation begins with a
disc containing cell wall
materials
Cleavage
• A cell
furrowplate forms
between the two nuclei
Cleavage furrow Contracting ring of
microfilaments
Daughter cells
Cytokinesis in plant cells
• Formation begins with a disc containing cell wall materials
• A cell plate forms between the two nuclei
Cell wall
Vesicles containing
cell wall material
New cell wall
Cell plate
Daughter cells
Benign vs. malignant tumor
• Benign tumor:

– abnormal mass of normal cells
Malignant tumor:
• Masses of cells that result from the reproduction of cancer
cells
• Cancer
– Disease caused by cells that loose their ability to
control rate of division
Meiosis
• Organisms that reproduce sexually have
specialized cells called gametes
• Gametes are the result of a type of cell
division called meiosis
Diploid and haploid
• Almost all human cells are diploid or containing two
homologous sets of chromosomes
2n = 46
• Eggs and sperm cells (gametes) are haploid or
containing a single set of chromosomes
n = 23
HUMAN KARYOTYPE
A display of all the 46
chromosomes of an
Individual.
9.5 page 2
ORGANISM (Genus species)
NUMBER OF CHROMOSOMES
 Homo sapiens (human)______________________________46
 Mus musculus (house mouse)_________________________40
 Drosophila melanogaster (fruit fly)_____________________8
 Caenorhabditis elegans (microscopic roundworm)_________12
 Saccharomyces cerevisiae (budding yeast) ______________32
 Arabidopsis thaliana (plant in the mustard family) ________10
 Xenopus laevis (South African clawed frog)______________36
 Canis familiaris (domestic dog)________________________78
 Gallus gallus (chicken) ______________________________28
 Zea mays (corn or maize)____________________________20
 Muntiacus reevesi (the Chinese muntjac, a deer) _________23
 Muntiacus muntjac (its Indian cousin) __________________6
 Myrmecia pilosula (an ant) ___________________________2
 Parascaris equorum var. univalens (parasitic roundworm)___2
 Cambarus clarkii (a crayfish)__________________________200
 Equisetum arvense (field horsetail, a plant)______________216
Horsetail
MITOSIS
Meiosis
haploid egg and sperm
diploid zygote
In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis
produces an embryo with numerous cells that continue to multiply and develop.
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis
MEIOSIS
MITOSIS
Original diploid cell
2n
2n
2n
2 diploid daughter cells
Genetic variation is a result of two
processes that occurr during meiosis:
• Independent assortment of chromosomes, and
• Crossing over
• During metaphase I, the independent assortment
of chromosomes that end up in the resulting cells
occurs randomly
• Crossing over:
exchange of genetic
material between
homologous
chromosomes during
prophase I of meiosis
• Genetic recombination: new combination of
genetic information in a gamete as a result of
crossing over during prophase I of meiosis
(pages 195, 200, & 201)
TYPE OF CELL (that undergoes
this division)
# OF CELL DIVISIONS
Starts/ends as diploid or
haploid cell
# OF DAUGHTER CELLS
# OF CHROMOSOMES AFTER
DIVISION
EXCHANGE OF DNA (Y/N)
UNIQUE OR IDENTICAL CELL
AFTER DIVISION
MITOSIS
MEIOSIS
Development of egg and sperm
Onion Root Cell Observations
• Using the largest magnification (X400), find a section of
the onion root (towards the tip works better).
• Count only the cells in one of the quadrants.
• Try to find the different stages of cell division, and fill out
the table bellow as accurately as you can.
Phase
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total # of cells
# of cells
%
Time/min.