Download Chapter 10: Cell Growth and Division

Chapter 10:
Cell Growth and Division
Section 10-1
Cell Growth
How Do Living Things Grow?

Cell division allows living things to grow, and
replace old cells.

Some organisms use it for asexual
reproduction.
Limits to Cell Growth
Cells can only grow so big for two reasons:
1. DNA Overload:

DNA (1 copy) holds information for an entire cell so
as a cell gets larger it puts more demands on its DNA.

Example: A library has only a certain number of
books. If a town doubles or triples in population
there wouldn’t be enough books for everyone.
2. Exchanging materials:

Nutrients enter and waste products leave
cells through the cell membrane.

Lower surface area to volume ratio = worse
at exchanging nutrients and waste.
Ratio of Surface Area to Volume

As a cell grows, surface area to volume ratio decreases.
Area = L x W x 6 sides
Volume = L x W x H
1 cm
2 cm
4 cm
A = 6 cm2 A = 24 cm2 A = 96 cm2
V = 1 cm3 V = 8 cm3 V = 64 cm3
Surface Area / Volume =
6/1
3/1
1.5/1
Section 10-2
Cell Division
Cell Division

Cell division – process by which a cell divides
into two new daughter cells


This solves problem of material exchange by
reducing cell volume.
Before cell division, cells replicate their DNA.

This solves problem of DNA overload because
each new cell gets a copy of DNA.
Chromosomes

Chromosome = a very long strand of
DNA tightly wound around proteins.

Every species’s cells contain a certain
number of chromosomes.
(ex. Human cells – 46, jack jumper
ant cells - 2, adders-tongue fern cells 1260)
Chromosomes

Cells (with one exception, see Ch. 11)
have two non-identical copies of
every kind of chromosome. These
copies are called homologous
chromosomes.


One copy came from Mom, one copy
came from Dad.
Human cells have 23 kinds of
homologous chromosomes = 46 total
chromosomes in each cell.
Chromosomes

When a cell is preparing to
divide, it replicates its
DNA, making a perfect
identical copy of each
chromosome.

The identical copies remain
attached to each other.
They’re called sister
chromatids.
Chromosomes Practice

Are these pairs of homologous chromosomes
or sister chromatids?
Chromosomes Practice

This image shows
homologous
chromosomes
after DNA
replication into
sister chromatids.
Point to a pair of
each…
The Cell Cycle

Cell Cycle – “life cycle of a cell,” the series of
events that cells go through as they grow and
divide

After the cell divides, the two new daughter
cells begin the cell cycle again.
Cell Cycle
Cell Cycle
The Cell Cycle

Phases of the cell cycle:
• G1 phase – cell growth
• S phase – DNA replication
interphase
• G2 phase – rapid metabolism
• M phase – Mitosis - division of the nucleus
Cytokinesis - division of the cytoplasm

http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the
_cell_cycle_works.html
Interphase – G1, S, and G2

Interphase = “normal life.”


DNA is unwound and chromosomes are not visible.
Nucleus bound by nuclear membrane
Purpose and Results of
Mitosis and Cell Division

Purpose – to create more of the same type of cell
so an organism can grow and replace old cells

Results – 2 new daughter cells that are genetically
identical to each other and to the original cell
M phase (includes Mitosis)
Mitosis is divided into four phases:
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
(part of M phase but
not part of mitosis)
Prophase



In Preparation for division, DNA condenses into
visible chromosomes.
Centrioles move to opposite sides of the cell and
spindle fibers form.
Nuclear membrane breaks down.
Metaphase

Chromosomes line up across the Middle of the cell
and are connected to the spindle.
Anaphase

Spindle fibers shorten, pulling the duplicated
chromosomes Apart to opposite sides of the cell.
Telophase


Two new nuclear membranes form around the
chromosomes at opposite ends of the cell.
Chromosomes unravel and lose their distinct shape.
Cytokinesis


Cytoplasm pinches in half, the new daughter cells
move apart.
Each daughter cell immediately goes back into G1
of interphase.
Models





Long string = Cell membrane
Short string = Nuclear membrane
Jujubes = Centrioles
Twizzlers = Spindle fibers
Each cell has 6 chromosomes

Gummi worms = Chromosome #1


Sour worms = Chromosome #2


Different colors = homologous chromosomes, same color = sister
chromatids
Different colors = homologous chromosomes, same color = sister
chromatids
Good n’ Plenties = Chromosome #3

Different colors = homologous chromosomes, same color = sister
chromatids
Section 10-3
Regulating the Cell Cycle
Controls on Cell Division

Normally, cells stop dividing when they come in contact
with other cells.
Example:
 Cells placed in a petri-dish grow and divide until they form
a thin layer covering the bottom.
 If cells are removed, cells bordering the open space divide
until they have filled the space and then stop.
Uncontrolled Cell Growth

Cancer – mutations to DNA in genes that control the cell
cycle result in rapid, uncontrolled cell growth
cancer
normal
http://scienceeducation.nih.gov/supplements/nih1/cancer/activities/activity2_animations
.htm
Section 11-4
Meiosis

Reminder: homologous chromosomes
Example:
 A body cell in an adult fruit fly has 8 chromosomes,
as shown in the drawing below.

4 chromosomes came from dad, and 4 came from
mom. The two sets of chromosomes are homologous.
Diploid and Haploid Cells

Diploid (2n) – cells containing homologous
chromosomes


Example: all body cells except sex cells
Haploid (n) – cells containing only one of
each kind of chromosome

Example: sex cells or gametes (sperm and egg
cells)
Diploid and Haploid Cells

Diploid vs Haploid before DNA replication
(no sister chromatids)
Diploid and Haploid Cells

Diploid vs Haploid after DNA replication
(with sister chromatids)
Why are reproductive cells haploid?
• A sperm cell (haploid) and an egg cell (haploid) combine to
create the first cell of a new organism (diploid).
Sperm
1 set
1 set
Egg
Humans
Zygote
(Baby)
2 sets
Meiosis

Meiosis - a process of nuclear division that produces
gametes, new cells with half of the original cell’s
genome
Meiosis

Meiosis goes through two divisions instead of one.
Meiosis
Crossing Over

Crossing over – portions of
homologous chromosomes
are exchanged


Happens in Prophase I, at the
very start of meiosis
Helps ensure that every
sperm and egg cell is unique
Meiosis

Result: Meiosis
produces four
haploid daughter
cells (gametes) that
are all genetically
different from each
other, and from the
original cell.
Animations

http://highered.mcgrawhill.com/sites/0072495855/student_view0/cha
pter28/animation__how_meiosis_works.html

http://highered.mcgrawhill.com/sites/0072495855/student_view0/cha
pter28/animation__comparison_of_meiosis_a
nd_mitosis__quiz_1_.html
Mitosis
Meiosis
to grow and
replace old cells
make gametes or
reproductive cells
2
4
Chromosome Number
(diploid or haploid)
diploid
(2 sets)
haploid
(1 set)
Genetic Relationship
to Original Cell
identical
different
body cells
gametes
Purpose for Organism
Number of Cells
Produced
Type of Cells Produced
Mitosis
Meiosis
to grow and
replace old cells
make gametes or
reproductive cells
2
4
Chromosome Number
(diploid or haploid)
Diploid->Diploid
Diploid->haploid
Genetic Relationship
to Original Cell
identical
different
body cells
gametes
Purpose for Organism
Number of Cells
Produced
Type of Cells Produced