10-1 Cell Growth
Growth and Development!!
When Do New Cells Need to Form?

A. Growth - More cells

B. Maintenance (repair and replacement)-->
intestinal lining/RBC’s)

C. Asexual reproduction

D. Formation of sex cells (Meiosis)
Limit of cell size?
1. TOO SMALL - There will not be enough
room for all the organelles to carry out the
processes needed.
2. TOO BIG!: Cell membrane
cannot control all movements of
materials

The larger a cell
grows the more
trouble it has…

moving enough
nutrients in

Moving all the
waste materials
out
Problem with Being Too Big!!
The volume gets too big for the surface area.
 The cell membrane cannot control all the
movement in and out when the volume is too
large.
 Your cells cannot too large either. The
surface area must be in the correct ratio of
the volume.
 Neurons are very long and skinny so that
ration is correct.

Radius
1cm
Radius 1cm
Radius 2cm
Radius 3cm
2___
= _____
S.A.S.A.
= __13cm
S.A. = ___50cm2__
S.A.
S.A.
= __113cm
= _____ 2_
3____
= ______
V =V__4cm
V = __33cm3____
V =V___113cm
= ______3___
RatioSA:V
SA:V==_13:4
___
Ratio
or 3.25:1__
Ratio SA:V =
50:33_or 1.51:1
Ratio
Ratio
SA:V
SA:V
= ___
=
_113:113 or 1:1__
S.A. = 4 (pi) r 2
1. As the spheres get larger what happens to the SA:V ratio?
3rd problem: DNA overload
rd
3
Problem - Too Big
3. DNA overload
 Your DNA controls all activities in
the cell. When the cell gets too big
then the DNA cannot control all
activites.
Cells Divide at Different Rates
 The
rate of cell division is determined by
the body’s need for that type of cell.
 Nerve cells do not divide because they
do not die like our skin cells.
 A new layer of skin is replaced every 3
weeks. The lining of your intestines has
to be replaced often because of the
wear and tear. This is also skin cells.
The Cell Cycle and Mitosis
Cell Cycle – life of a cell
 The
life of a cell. It has a pattern of
cell growth, DNA replication, and
cell division. Results in two new
daughter cells.
The Cell Cycle
 The
sequence of growth and
division of a cell.
 95% of cell cycle in
interphase(growth)
 5% of cell cycle in
mitosis(division)
3 Main Events of a Cell Cycle
1. Interphase
2. Mitosis Phase –
nucleus dividing
 G1 - growth
 Prophase
 S – DNA
replication
 Metaphase
 G2 – growth
 Anaphase
and prepare
 Telophase
for division
3. Cytokinesis –
cell division
What’s
Missing?
M Phase, Cell Division and Mitosis
Cell Cycle

http://www.cellsalive.com/mitosis.htm

http://www.johnkyrk.com/mitosis.html
The Cell Cycle - series of events that cells
go through as they grow and divide

The cell cycle is
divided into two
halfs
 Interphase period of the cell
cycle between
cell divisions
 Mitosis phase and
cytokinesis –
period of time
when mitosis and
cell division
occurs
Definitions
Histones
 Telomeres
 Somatic cells
 Chromatin
 Chromosomes
 Centromeres
 Spindle fibers

Some Definitions



Histones: proteins that DNA will wrap around. This
helps the DNA to fit.
Telomeres: End of DNA molecules to prevent them
from attaching to each other. They do not contain
genes.
Somatic Cells – body cells


Produced through mitosis
Has 46 chromosomes (23 pairs)
Chromatin - A complex of DNA and proteins
in the cell nucleus that condenses to form
chromosomes during cell division(loose
DNA).
 Chromosomes – Condensed Chromatin(X)
 They are the same stuff, just in different
forms
 Centromeres: Center point where
chromatids are attached.
 Spindle Fibers - Fibers that pull part the
chromosomes during mitosis.

Chromatin condenses in chomosomes
before mitosis begins

Chromatin

Chromosomes
Parts of Interphase
 G1
Phase(growth)
Cell grows
Synthesize new
proteins and
organelles
Doing their jobs
Longest phase
of cell cycle
S Phase
S
Phase(synthesis)
 Chromosomes(DNA) are replicated
 Key proteins associated with
replication are made (centromeres
Gap 2 Phase
 G2
Phase(growth)
Shortest of the 3 phases of
interphase
Organelles and molecules for cell
division are produced (centrioles)
Check-up phase before mitosis
G - 0 Stage
This is a stage of interphase that
SOME cells enter. Cells such as
nerve and white blood do not divide
often so they enter this stage of rest.
Animated Cycle
http://www.cellsalive.com/cell_cycle.htm
What stops cell from growing?

Proximity to neighbor cells.
 Cells in a petri dish will continue to grow
until they come into contact with other
cells.
 Similarily, skin around a wound
After a cell has quit growing, it is time to
divide!!!
Mitosis
MITOSIS
Mitosis
Division of the nucleus.
Followed by cytokinesis!!!
The daughter cells are identical to
one another and to the original
parent cell.
Mitosis
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase
Longest phase of mitosis
 Chromatin condenses into
chromosomes
 Spindle fibers form and
attach to centrioles
 Nuclear membrane
dissappears
 Nucleolus breaks down

Prophase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase
The cell prepares for nuclear
division

Animal Cell

Packages DNA into
chromosomes

Plant cell

Packages DNA into
chromosomes
Metaphase
Centromeres line up
across the center of
the cell
 Spindle fibers
connect to
centromeres

Anaphase
 Chromosomes
are pulled apart by
spindle into
individual
chromatids.
 The chromatids
are now
considered
Chromosomes!!
Anaphase
 Centromeres
split
 Sister chromatids are pulled
apart to opposite poles of the
cell
 Each chromatid is now a
separate chromosome
Telophase
 Nuclear
envelopes (2) and
nucleolus reform
 Chromosomes begin to uncoil
 Spindle fibers disappear.
Mitosis Animation
http://www.cellsalive.com/mitosis.htm
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Cytokinesis
 Cytoplasm
divides
 Two new daughter cells are
now separate
http://www.johnkyrk.com/mitosis.html
Cytokinesis
The cytoplasm pinches in
half
 Animal - cleavage furrow
 Plants - cell plate

In plant cells, a cell plate forms. The cell plate is
synthesized by the fusion of multiple membranebounded vesicles. Their fusion supplies new plasma
membrane for each of the two daughter cells. Synthesis
of a new cell wall between the daughter cells then
occurs at the cell plate.
Apoptosis
 Cell
death. Factors that signal
genes to produce self
destructive enzymes. Not sure
why.
 EX: webbing of toes on an
embryo.
Cyclins
Protein that
controls cell
division..
They can make
cells grow in a
petri dish.
Doesn’t work on
all cells.
Controls on Cell Division
Cancer
Class of disease caused by uncontrolled cell
division. Arises when the regulation of the
cell cycle breaks down. The cells continue to
divide with the absence of internal and
external growth factors.
 Benign tumor: cancer cells remain in one
mass and usually can be removed.
 Malignant: cancer cells break away from the
cancer cells to other parts of the body.

Why are cancer cells so
dangerous?

Cancer cells cannot perform the duties
needed by the body. Too many cancer cells
and the body cannot perform the processes
needed to live. A large tumor can apply
pressure to other organs and affect the
processes of organ.
What causes cells to form
cancer?
Cancer cells comes from regular cells that
have damage in one of the two genes that
makes the proteins for cell cycle regulation.
 Oncogene: gene that accelerates the cell
cycle.
 Gene 2 : breaks cell cycle.
 A mutation in these 2 genes can be inherited
or a carcinogen can cause a mutation in
these genes.

Causes of Cancer

Carcinogen: Substances known to cause the
cell cycle genes to mutate and cell divide
uncontollably.

Various forms of cancer have many causes
 Smoking
 Radiation
 Viral
infections
The common thread in all cancers is that
control over the cell cycle has broken down.
 Over 50% of cancer cells have a defect in
the p53 gene.

p53 antioncogene


p53 is a tumor
suppressor gene
found mutated in
about half of
human cancers.
It encodes a gene
regulatory protein
that is activated by
damaged DNA and
is involved in
blocking further
progression of the
cell cycle.
Oncogenes
SRC, proto-oncogene tyrosine-protein kinase
Treatments for Cancer

Radiation and chemotherapy – used to kill
the cancer cells and stop division. They kill
good and bad cells.
Stem Cells
Stem cells are a type of body
cell that have the ability to
1. Divide and renew
themselves
2. Remain undifferentiated
3. Develop into a variety of
specialized cells.