Transcript Cell Division

Unit 2
Cell Division
Mitosis and Meiosis I and II
Mitosis Word Meanings
• Chromosome
– Etymology: Greek : Chromo = colored soma = body
• Centromere
– Centro= center mere= part
• Inter
– Etymology: Latin: between
• Pro– Etymology: Greek: before
• Meta– Etymology: Greek: after
• Ana– Etymology: Greek: up
• Telo– Etymology: Greek : end
• Cytokenesis
– Etymology: Greek: Cyto = cytoplasm kenesis = movement
I.
Reasons why a cell needs to divide.
1. Destroyed cells need to be replaced.
2. Cell size
a. Most living cells are between 2 and 200
micrometers in diameter (3 feet = 1 meter = 1
million micrometer)
b. Limitation of cell size
i.
Surface area to volume ratio
1.
2.
ii.
Increase cell size will increase volume of cell
As cells grow, the amount of surface area becomes
too small to allow materials to enter & leave the cell
quickly enough by diffusion.
Diffusion (see unit 1)
1.
2.
fast & efficient over short distances
If cell gets too large, would decrease diffusion.
iii.
The nucleus
1. DNA in the nucleus is copied to make proteins
which run the cells activities in the cytoplasm.
2. Cell size is limited by the amount of proteins the
DNA is able to make to control the cell.
II.
DNA Packing (occurs before cells divide)
a.
DNA is a very long thin molecule (can’t see it)
i.
ii.
In order to fit in the nucleus it has to get really compact (=
packed in closely).
The DNA does this by wrapping around proteins called
Histones, and folding in on itself
i.
b.
This is known as Chromatin. (We can see this)
When Chromatin is wrapped up on itself and takes on a
distict shape (looks like an “X”) it is known as a
Chromosome (We can see this too)
III. Chromosomes
1.
Human cells have 46 Chromosomes
a.
b.
c.
Humans get 23 from the mother and 23 from the father.
Before the DNA wraps up into a chromosome, the DNA gets
copied.
Before cell divides each DNA piece winds up into a c’some
i.
ii.
d.
One side of the chromosome is the original chromosome
The other side of the chromosome is the copy of the original
chromosome.
When a Chromosome is paired we call each side a
Chromatid. (You have 2 Chromatids for each Chromosome)
a.
b.
Chromosomes pairs are held together by a centromere.
When the chromatids separate into separate nuclei we call
them chromosomes again.
Chromatids
Centromere
Before DNA Replication
1 pair per type of
chromosome
Individual chromosomes
• 1 from each parent
Dad Mom
After DNA Replication
2 pairs per type of
chromosome
Homologous Pairs
IV. Cell Cycle
i.
Interphase – before cell division
1.
G1 phase
i.
ii.
2.
cell growth
production of new organelles
G0 (G zero)
i.
ii.
iii.
iv.
3.
period when cell is not preparing to
divide.
Here cells lack growth factors
Cells stay in the G0 until there is a
reason for them to divide.
Ex. Muscle, brain, nerve cells
S phase = Double the DNA
i.
ii.
4.
DNA replication (duplicate)
Go from 46 to 92 single chromosome
molecules per cell in humans
G2 phase
i.
cell prepares to divide
ii.
M phase = Mitosis – Cell Division
1.
Prophase
i. chromosomes shorten, thicken, and become visible
ii. nucleus and other organelles break down and disappear
iii. Organelles called centrioles begin to make spindle fibers
2. Metaphase
i.
spindle fibers become present and attach to
centromeres of chromosome pair.
ii. chromosomes line at center of cell (metaphase plate
= equator)
3. Anaphase
i.
The Chromatids are pulled apart towards polar ends
of the cell.
4. Telophase
i. New nuclei form around each set of chromosomes
ii. two new cells start to take shape
iii. chromosomes begin to make proteins
5. Cytokinesis
a. In animal cells
i. Animal cells undergo cytokinesis by pinching off
along their equator
ii. This works because their membrane is flexible.
b. In plant cells
i.
Plant cells cannot do the same as animal cells
because of their cell wall.
ii. Plant cells send vesicles filled with cell wall material
to their equator where they fuse together.
iii. This fusion creates cell plates that fuse with the cell
wall separating the two cells.
V.
Cancer
i. It is the disease where the
body’s cells DO NOT STOP
mitosis.
ii. Results in tumors forming
throughout the body.
a. A tumor is a bunch of cells in
one area of the body that
keep dividing.
b. These cells can then move
on to other parts of the body
causing tumors to develop in
other regions.
iii. Cancer kills by causing your
organs to malfunction.
VI. Cell Differentiation
i.
Unspecialized cells develop into mature forms and
functions
a.
b.
Each cell has a full set of DNA
BUT, each type of cell uses only specific genes on the DNA to
carry out its functions
ii. Stem Cells
a.
b.
Can develop into a variety of cell types
Will divide by mitosis into either two stem cells, or, a stem
cell and a specialized cell.
Mitosis Pop Quiz
1.___________________________
2._________________________
3.___________________________
4.__________________________
Meiosis Word Meanings
• Homologous
– Etymology: Greek homologos : to agree
– having the same position, value, or structure
• Tetrad
– Etymology: Greek
– a group or arrangement of four
• Dyad
– Etymology: Late Latin dyas, from Greek, from dyo
– : pair; two individuals
• -ploid
– having or being a chromosome
• Di– Etymology: Latin, from Greek; akin to Old English twi– twice : two : double
• Ha– Etymology: Greek :single
• Somatic cells and Gametes
– Somatic cells are body cells.
• Make up most of your body cells.
• These are diploid (2n)
– Have two sets of chromosomes.
– 1 set from father & 1 set from mother
– Gametes = sex cells(sperm/egg cells)
• These are haploid (n)
– Have only one set of chromosomes
– Types of Chromosomes
• Autosomes – contain genes not
associated with sex
• Sex chromosomes – directly control
sexual traits.
Meiosis – The creation of sex cells
Interphase (G1, S, G2)
• All your cells start off as diploid cells
= Diploid (2n): cell with two of each kind of
chromosome (In humans = 46 [23 from
each parent])
• G1 – Cell grows; DNA is long and stringy and
is not visible. (so the DNA can be copied)
• S – DNA gets replicated (copied).
• G2 – Cell continues growing and prepares to
divide.
Meiosis I
Prophase I
1. The chromatin wind-up, creating chromosomes
which can now be seen.
2. Centriols create Spindle Fibers
3. Nuclear envelope disappears
4. Each chromosome pair then actively seeks
out its homologous chromosome pair.
–
–
Homologous pairs are about the same size and shape
This is called a tetrad (four chromatids)
– Crossing Over will now happen.
• where two non-sister chromatids exchange genetic
material.
Before DNA Replication
1 pair per type of
chromosome
Individual chromosomes
• 1 from each parent
Dad Mom
After DNA Replication
2 pairs per type of
chromosome
Homologous Pairs – each individual
chromosome has been copied
Prophase I
Metaphase I.
1. The spindle fibers attach to the centromere on
each chromosome pair.
2. Homologous chromosomes are lined up on the
metaphase plate (equator) by the spindle fibers.
3. 2 rows of 23 chromosome pairs = 46 pairs total
Anaphase I
1. The tetrad gets pulled apart = homologous chromosomes
separate.
– CHROMATIDS DO NOT GET PULLED APART YET!
2. Each homologous chromosome moves to opposite poles.
Telophase I / Cytokenesis
1. Individual nuclear envelopes begin to surround
the separate chromosome pairs
2. Cytokenesis separates the one cell in two.
END OF MEIOSIS I
Two cells are created each with 23 chromosome
pairs
Meiosis II
Prophase II
1. Each dyad (2 Chromatids = 1 Chromosome pair)
are connected by a centromere.
2. Nuclear envelope disappears
3. The centrioles create spindle fibers again.
Metaphase II
1. The spindle fibers attach to the centromere on
each dyad (1 Chromosome pair = 2 Chromatids).
2. The dyads are lined up on the metaphase plate
(equator) by the spindle fibers.
3. 1 row of 23 chromosome pairs in each cell.
Anaphase II
1. The individual sister chromatids from each dyad
get pulled apart by the spindle fibers
2. Each sister chromatid ends up on opposite poles
of the cell
Telophase II / Cytokenesis
1. The shape of the cell changes, beginning to form
two cells.
2. New nuclei form around each set of chromosomes
3. The cytoplasm of both cells divides once again.
4. Four gametes (= sex cells) are now created
END OF MEIOSIS II
Four unique haploid cells are created, each with a half set
of chromosomes compared to the original (Original Parent
cell had 46, each daughter cell has only 23 chromosomes).
= Haploid (n): cell with only 1 of each kind of chromosome (in
humans = 23 chromosomes)
Mitosis: Chromosome Number Flow
Interphase
Mitosis
46 individual
chromosomes
2n
46 chromosome
pairs
46 individual
chromosomes
2n
46 individual
chromosomes
2n
Meiosis I & II Chromosome Number Flow
Meiosis I
Interphase
46 individual
chromosomes
2n
46 chromosome
pairs
23
chromosome
pairs
23
chromosome
pairs
Meiosis II
23 individual
chromosomes
n
23 individual
chromosomes
n
23 individual
chromosomes
n
23 individual
chromosomes
n