Chapter 10
Cell Division
Ch. 10: Section 1
I. Limits to Cell Growth/Size
A. DNA “Overload” – If a cell grows too
large, its DNA could no longer serve the
needs of the entire cell
B. Exchanging materials – if a cell is too
large, is struggles to move enough
nutrients & wastes throughout the cell
and to the cell membrane
II. Surface Area to Volume Ratio
A. Surface Area = length x width x # of sides
B. Volume = length x width x height
C. Surface Area to Volume Ratio = SA/V
D. Volume increases more rapidly than
surface area, causing the ratio to
decrease
E. 2 lane main street into a town will
experience more traffic as town gets
bigger, and it takes longer to get to
center of town as size of town increases.
II. Surface Area to Volume Ratio (cont)
Calculations:
All sides = All sides = All sides =
Cell Size:
Surface Area
(length x width x 6)
Volume
(length x width x
height)
Ratio of Surface
Area to Volume
(SA/V)
1cm
2cm
3cm
II. Surface Area to Volume Ratio (cont)
Calculations:
All sides = All sides = All sides =
Cell Size:
1cm
2cm
3cm
Surface Area
(length x width x 6)
6 cm2
24 cm2
54 cm2
Volume
(length x width x
height)
1 cm3
8 cm3
27 cm3
6/1 =
6:1
24/8 =
3:1
54?27 =
2:1
Ratio of Surface
Area to Volume
(SA/V)
Ch. 10: Section 2
I. Why cells divide/reproduce
A. Growth – new cells are needed to grow
tissues and organs
B. Replacement & Renewal – old/damaged
cells die & are replaced with new
C. Reproduction
1.
2.
unicellular organisms divide to make new
organisms
multicellular organisms divide cells to make
sex cells (gametes).
II. Chromosome Structure
A. Gene – DNA is a large molecule broken
down into hereditary units called genes
•
DNA is organized & packaged into
chromosomes during cell division
B. Chromosome – DNA wound or coiled
tightly around proteins (histones)
•
•
Prokaryote Chromosome – a single, circular
loop of DNA
Eukaryote Chromosome – many linear DNA
molecules packaged into chromosomes
C. Structure – fully condensed, duplicated
•
•
•
•
A chromosome is made of 2 identical
halves. Each half is called a chromatid.
A centromere holds 2 chromatids together
to make a chromosome.
DNA is packaged as a chromosome only
during cell division, after it has been
copied.
When a cell is not dividing, its DNA is
packaged more loosely as chromatin.
III. Chromosome #’s - each species
has a different number of chromosomes
A. Sex Chromosomes – and X or Y
chromosome
1. They determine the sex of the
individual
2. Female = XX
Male = XY
B. Autosomes – all remaining
chromosomes
1. In humans: 44 autosomes + 2 sex
chromosomes = 46 total chromosomes
2. The 44 autosomes in a human are
actually 22 pairs. An individual gets a
copy of each chromosomes from each
parent.
C. Homologous Chromosomes – a pair
of chromosomes
1. A human has 22 homologous
chromosome pairs
2. A homologous pair are the same size,
shape, and contain the same types of
genes for the same traits.
 Each chromosome can have
different specific genes than its
homologous pair
D. Diploid Cells
1. Are cells having all homologous pairs and
2 sex chromosomes
2. All cells except gametes
(gametes = sex cells: egg and sperm cells)
3. Diploid cell are abbreviated as 2n, where
n = # of 1 set of chromosomes.
4. Also called body cell, or somatic cells.
5. The chromosomes of diploid cells can be
arranged and studied using karyotypes.
E. Haploid Cells
1. Cells that contain only 1 chromosome
from the pair of homologous
chromosomes and 1 sex chromosome.
2. Haploid cells are abbreviated as n.
3. Haploid cells are gametes.
Chromosome # Example
A male human has 46 total chromosomes.
(A chromosome is made of 2 chromatids, duplicated
copies of the same DNA molecule)
• # of autosomes =
• # of sex chromosomes =
– The sex chromosomes are
• # of homologous pairs =
• Diploid # (2n) =
• Haploid # (n) =
IV. Eukaryote Cell Cycle
A. Cell Cycle – repeating events of growth
and division during the life of a cell
B. Interphase – time when cell is not
dividing
1. G1 Phase – cells grows rapidly as it makes
more organelles
2. S Phase – DNA/chromosome is copied
3. G2 Phase – cell continues to grow and
makes organelles for cell division
4. G0 Phase – when cell doesn’t divide
(instead of G1, S, & G2 Phases)
C. Mitosis – division of the nucleus (DNA)
1. Prophase – 1st step
• DNA is packaged into chromosomes
• Nucleolus and nuclear membrane
break apart
• Centrioles move to opposite ends of
the cell
2. Metaphase – 2nd step
• Spindle fibers coming from the
centrioles attach to the centromeres
of the chromosomes
• Chromosomes line up in the middle
of the cell
3. Anaphase – 3rd step
• Spindle fibers pull chromatids apart
at the centromere
• Each chromatid is now considered a
chromosome!
4. Telophase – 4th (last) step
• Spindle fibers disappear
• Nuclear envelope reforms around
each set of chromosomes
D. Cytokinesis
1. Begins during telophase.
2. Is the division of the cell/cytoplasm.
• Animal cells: cell membrane pinches
inward making a cleavage furrow.
This continues until 2 cells are formed.
• Plant Cells: a cell plate forms between
the 2 sets of chromosomes.
***Mitosis happens in somatic cells and makes
2 diploid cells!
Mitosis in a Plant Cell
Mitosis in an Animal Cell
E. Controls on Cell Division
1. Physical contact
• Cells tend to divide until a space has
been filled.
• Once that space has been filled, or the
cells contact each other, they stop
dividing.
2. Cell Cycle Regulators
• Cyclin – protein that regulates the cell
cycle
• High levels of cyclin = cell division
• Low levels of cyclin = Interphase
F. Uncontrolled Cell Growth
1. Cancer – cells lose the ability to control
cell divison/growth
2. Cancer cells do not respond to the
signals that regulate the growth of most
other cells.
3. As a result, they form masses of cells,
tumors, that can damage the
surrounding tissues.
Section 11-4: Meiosis
Meiosis – cell division that halves the
number of chromosomes in new cells,
making haploid cells
*Recall, haploid cells in human are
egg/sperm cells, called gametes, and contain
23 chromosomes.
Stages of Meiosis
I. Interphase
A. cells go through G1, S, and G2 phases;
B. DNA is copied and cells grow larger.
II. Meiosis I
A. Prophase I
1.
DNA is coiled into chromosomes & nucleus
breaks down
2. Centrioles move to ends of cell; spindle
fibers appear
3. Chromosomes pair up (in homologous pairs)
and twist together.
– Portions of a chromatid can break off and
reattach to the identical chromatid on its
homologous chromosome = crossing over
Prophase I and Crossing Over
B. Metaphase I
1. Homologous chromosomes line up
randomly in the center of the cell
2. Spindle fibers attach to the centromeres
C. Anaphase I
1. Spindle fibers pull homologous
chromosomes apart.
2. The direction the chromosomes are pulled
is random = independent assortment
D. Telophase I
1. Chromosomes move to opposite ends of
the cell
2. Cytokinesis occurs
**Meiosis I results in 2 new haploid cells
III. Meiosis II
• Begins immediately after Meiosis I.
• Both cells from Meiosis I go through
Meiosis II.
• DNA is not copied this time!!!!!!!
A. Prophase II – spindle fibers reform,
centrioles move to opposite ends of cell
B. Metaphase II – single chromosomes
line up in the middle of the cell
C. Anaphase II – spindle fibers attach at
centromeres and pull chromatids apart
D. Telophase II – chromatids move to
opposite ends, and nucleus forms
around them and cytokinesis occurs
**Meiosis II results in 4 new Haploid cells.
Stages of Meiosis II
IV. Meiosis Forms Gametes
A. The 4 haploid cells produced in Meiosis
are gametes (sex cells = egg/sperm)
B. Spermatogenesis – production of sperm
cells
C. Oogenesis – production of mature egg
cells or ova (singular = ovum)
V. Genetic Variation in Meiosis
A. Crossing Over – switching of DNA
between chromatids of homologous
pairs; occurs during prophase I
B. Independent Assortment – each
homologous pair is separated
independent of how the other pairs
are separated.
C. Random Fertilization – of the 4
gametes produced in meiosis, any one
can fertilize (join) with another gamete