Chapter 10 (pages 240-252)

There are 2 limitations that cause cells
to divide instead of grow indefinitely
 With
a partner, take a few minutes to think
of what these 2 limitations might be!
Why do cells divide instead of growing
indefinitely?
There are 2 limitations that cause cells to
divide instead of grow indefinitely
 Larger the cell, more demands placed on DNA

 Library

Larger the cell, harder to move nutrients and
wastes across the cell membrane
 Volume increases much
more rapidly than SA in a
growing cell – smaller ratio
 Town Road




In eukaryotic cells, chromosomes pass
genetic information from one
generation to the next
Made up of DNA and proteins
Not visible to the human eye because
the DNA and proteins are spread out
through the nucleus, but condense at
beginning of cell division
We have 46 chromosomes
Centromere
center
attachment
Sister
chromatids
Identical
replications of the
chromosome

Process by which a cell divides
into 2 new daughter cells
 Prokaryotes
– simple process
 Eukaryotes – bit more complex
Prokaryotes do not have organelles or a nucleus to
replicate, Eukaryotes do!

Interphase: time period between cell divisions

G1 phase


Cell growth
S phase
DNA replication
 Chromosome replication


G2 phase
Preparation for mitosis
 Organelle production


M phase


Includes mitosis and cytokinesis
Go phase

Cell is done dividing

Interphase: period of
growth that prepares the
cell for division
 Includes
G1, G2, and S
phase
 Cell size increases
 DNA replication
Division of the cell nucleus
4 Phases

Prophase
Metaphase
Anaphase
Telophase
1st and longest phase (takes
50-60% of the total time)
 Chromosomes become
visible
 Spindle starts to form
 fanlike microtubule
structure that separates
the chromosomes
 Nucleolus disappears and
nuclear envelope breaks
down

Short phase
 Chromosomes line
up across center of
cell
 Microtubules
connect the
centromere to the
2 poles of spindle

Centromeres split,
allowing sister chromatids
to separate and become
individual chromosomes
 Chromosomes move until
they are at opposite ends
of the cell
 Ends when chromosomes
stop moving

Final phase
 Chromosomes lose their
distinct shape
 A new nuclear envelope
forms around each cluster
of chromosomes

Cytoplasm
pinches in half
 Each daughter
cell has an
identical set of
duplicate
chromosomes


A structure known as
the cell plate forms
midway between the
divided nuclei
 The
cell plate gradually
develops into a
separating membrane
 A cell wall then begins to
appear in the cell plate
Cell Plate

On the half sheet of paper, answer the following
questions. Keep your half sheet at your desk!
1. In which phase of mitosis do the chromsomes
appear and become visible to the human eye?
 2. In which phase of mitosis do the chromosomes
line up in the middle of the cell?
 3. In which phase of interphase does the DNA
replicate?
 4. During which phase of mitosis does the nuclear
membrane (envelope) reappear?
 5. In which phase of mitosis do the centromeres
split?
 6. In which phase of interphase does cell growth
occur?


Cellular division in a multicellular organism is a
carefully controlled process
 Not
all cells move through the cell cycle at the same
rate and some do not continue to divide after
development

Don’t keep dividing:
Nerve cells
 Muscle cells


Do keep dividing:
Skin cells
 Digestive tract cells
 Bone marrow cells
 Blood cells (but wait, they don’t have a nucleus?!)


Scientists found a particular protein they associated
with cell cycle regulation – they help control the
cycle
 This
protein is called 
 Cyclin

is found in large quantities during cell division
However, cyclin is not the only regulator that plays a
role in cell division
 There
are both internal and external regulators that
affect the cell cycle
– regulate internal factors
of cell growth
 Example:
proteins that regulate mitosis so that it does
not occur until all chromosomes have been replicated
– regulate external
factors of cell growth
growth factors  present on the surface of
cells so they know when to stop/start dividing
 Example:
Controlled Cell Growth

Scientists have observed controlled cell growth in a
lab by using a petri dish with nutrient broth
 What
is a common reason why our cells are stimulated
to grow?

Uncontrolled cell growth is
extremely severe!
: disorder in the body in
which cells lose their ability to
control their growth
 Result
of cancer: cells divide
uncontrollably and form masses of
cells called tumors
 Cells break loose from the tumors
and spread to other parts of the
body
Brain Cancer

Some cancers have a cause
Tobacco Use
 Radiation Exposure


All cancer has 1 thing in common – the cell
has lost its ability to control cell division
A large number of cancers have been tied to a
defect in the p53 gene
 p53: regulator that halts the process of mitosis
until all chromosomes have been replicated
 If the cell starts dividing too early, it loses
valuable info it needs to regulate cell division
from there on out

Additional Vocabulary

Homologous chromosomes are
a chromosome pair that are
similar but not identical
One chromosome of
each homologous pair comes from
the mother and one comes from the
father
 Sister chromatids = identical!


Chromatin: DNA that is spread
out in a non-dividing cell
Name that phase….
Interphase
Prophase
Metaphase
Anaphase
Telophase
Oreo Mitosis! Yeah!