Chapter 10 and 11-4
Cell Growth and
Division
Cell Growth and Division
Organisms need to grow and
reproduce:
• Both require divisions of the
nucleus (Mitosis/Meiosis) and
the cytoplasm (Cytokinesis)
1. Growth
•
Mitosis- the division of the
cell’s nucleus into 2 identical
copies
2. Reproduction
•
Meiosis – the reduction of the
chromosomes by ½ to create
gametes for sexual
reproduction.
I. Cell Growth
A. Limits to Cell Growth
– As a cell grows larger the cell volume increases but the
surface area to volume ratio decreases.
– What does this mean?
Cells come in different sizes, in order to make
a multicellular organism cells must divide, not
just grow larger
Exchanging Material
1.
Larger cells have more
problems getting materials in
and out of the cell.
2. Doubling the cell size;
increases the amount of time it
takes for materials to enter and
leave.
a.
b.
O2, nutrients, monomers, water
enter
waste products such as CO2
leave, also proteins made by the
cell leave
3. How rapidly materials pass
across the membrane and get to
the center of the cell is a
function of surface area
4. The relationship of surface area (SA) to volume (V) is expressed
as a SA/V Ratio
Cell Sizes
Surface Area
lengthxwidthx6
Volume
Lengthxwidthxheight
Ratio of surface
area to volume
6 cm2
24
54 cm2
cm2
27cm3
1 cm3
6:1
8 cm3
3:1
2:1
5. The higher the SA/V ratio = the more efficient
transport of substances
• Example: If you wanted to chill a warm Coke,
would you use 3 large ice cubes or crushed ice?
vs.
• Answer: crushed ice (more surface area exposed to
cool down drink)
DNA Overload:
1. DNA must be able to
be transcribed fast
enough to create
mRNA to make
proteins for the cell to
function
2.
The DNA is limited to
the amount of mRNA
that can be produced
without significantly
slowing down the cells
activities.
B. Division of the Cell
1. Cellular division solves
both problems.
•
In order to grow larger,
more cells will be made
through the process of cell
division.
2. As an organism grows
larger, the number of
cells increases
3. Conception -1 cell, birth
– 1 trillion cells, adult 65 trillion cells
B. Division of the Cell
DNA
replication
4. The DNA must be copied, the cell divides and the daughter
cells have increased SA/V ratios
5. This allows for efficient exchange of materials and DNA
can fulfill protein manufacturing quota
II. Cell Division: Mitosis and Cytokinesis
A. Chromosomes: Structure
and Composition
1. Prokaryotes: circular form
(plasmids)
2. Eukaryotes: form distinct
shapes of chromosomes
3. Chromosomes are made
out of a material called
chromatin (DNA + histone
= nucleosome)
•
•
condenses into
chromosomes during cell
division (mitosis)
Coil and supercoiling of
nucleosome
http://www.biostudio.com/demo_freeman_dna_coiling.htm
4. Organisms vary in the number of chromosomes:
• Goldfish: 94
Potato:
48
• Dog: 78
Carrot:
18
• Humans: 46
Drosophila:
8
B. The Cell Cycle
1. During a cell cycle, a cell grows, prepares for
division, and divides to form 2 daughter cells,
each of which begins the cycle anew.
2. 2. Two phases:
1. Interphase = (growth, organelle and DNA replication)
2. M Phase = Mitosis & Cytokinesis
G1
M-phase
s
G2
C.
1.
Interphase
Normal cellular functions, DNA is not visible
(chromatin), growth and replication of DNA.
Involves 3 stages:
2.
G1 (Gap 1) – cell grows, proteins and organelles are
produced
ii. S - DNA synthesis/replication
iii. G2 (Gap 2) – organelles/structures required for cell
division are made
i.
D. Mitosis
* Nucleus divides into two identical nuclei
* Four phases include:
Prophase, Metaphase, Anaphase, Telophase (PMAT)
1. Prophase
• Longest phase of mitosis (5060% of time)
• Chromosomes start to become
visible
• Chromatin is coiled and
condensed
• Centrioles separate from each
other
• Spindle fibers begin to form
• Nucleolus disappears
• Nuclear envelope begins to
break down
2. Metaphase
• Shortest phase of
mitosis (a few
minutes)
• Chromosomes line up
at center of cell
(equator)
• Microtubules attach to
the centromere &
spindle poles which
forms an aster
3. Anaphase
• Centromeres split which then
separates the sister chromatids
• Individual chromosomes move
toward opposite poles
• Spindle grows larger
• Chromosomes are pulled toward
the poles where the centrioles
are located.
4. Telophase
•
•
•
•
•
Chromosomes begin to uncoil
Chromatin fibers are reformed
Nuclear envelope reforms
Spindle begins to breakdown
Nucleolus becomes visible in
each daughter nucleus
**MITOSIS IS NOW
COMPLETE!!
E. Cytokinesis
• Dividing of the cytoplasm and organelles
• Plant cells form a cell plate that becomes
the cell wall
• Animal cells: membrane pinches inward
Cell
plate
formin
g
Cell wall
Wall of
Daughter
parent cell nucleus
New cell wall
Vesicles containing
Cell plate Daughter
cell wall material
cells
Centrioles
Centrioles
Centromere
Nuclear
envelope
Daughter
Cells
Chromatin
Centrioles
Chromosomes
_______________
(paired chromatids)
Spindle
Centrioles
Individual
Chromosomes
Nuclear
envelope
reforms
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#
Animal Cell Division in White Fish Blastula
III. Rates of Cell Growth & Controls on Cell Growth
• Escherichia coli (E. coli) can
divide every 20-30 minutes under
ideal conditions.
• Ideal conditions cannot be
sustained forever.
• Every organism/type of cell grow
at varying rates - p249
• Some cells rarely divide if they
divide at all.
E.coli
– Example: nerve cells, heart cells,
muscle cells, red blood cells
• Cells that form linings are
frequently replaced which requires
cell division
– Example: Skin cells, blood cells
(marrow)
Skin Cell
A. Controls on Cell Division
1. Cells in the Lab:
1. Grown in a petri dish containing nutrient broth
(provides food for the cells)
2. Cells will grow until they form a thin layer then
stop
3. Cells contact other cells which signals cell
division to stop
• We don’t see multiple layer grow
3.
1.
5.
2.
4.
Figure 2: Cells in a petri dish will continue to grow until they
come in contact with other cells.
Question: What happens when you cut your finger or break your bone?
Answer:
The cells bordering the injury will begin dividing to fill
in the gap in the tissues that have been torn or
broken. This is the process known as healing.
B. Cell Cycle Regulators
controlled
1. Scientists wondered what ____________cell
division.
2. Tim Hunt and Mark Kirschner discovered
that cells in mitosis contained a protein that
when injected into a cell would cause the
formation of spindle fibers.
cyclins
3. Protein group known as ____________
regulates the cell cycle.
cell cycle
4. They rise and fall in time with the ________.
5. Cyclins _____________
the timing of the
regulate
eukaryotic
cell cycle in __________cells.
6. Two main groups of protein regulators
i. Internal Regulators: respond to
inside the cell
events __________________
.
Ex. Make sure cell doesn’t enter
mitosis until chromosomes have all
replicated
ii. External Regulators: respond to
outside the cell
events _________________________.
Ex. Embryonic growth and healing
C. Uncontrolled Cell Growth
• Cancer: a disorder in which some
cells have lost the ability to
control their own rate of growth
• Malignant Cells (cancer cells) will grow multiple layers and
develop into a tumor which
eventually will spread to other
areas of the body.
• Benign Tumors (NOT cancerous)
- self-contained and will not
spread to other areas.
2. Causes of Cancer:
a. Exposure to mutagens
(carcinogens)
1. chemical – compounds
within tar from cigarettes,
asbestos, thalidomide,
some pesticides
2. Diet – low fiber, high salt
with few veggies
3. Radiation (10%) – UV,
gamma
4. Viral (18%) – Hepatitis,
HPV
5. genetic defect (5%) – p53
gene
Consider the that is takes, on average, 24 hours (1,440 minutes) for onion root tip cells
to complete the cell cycle. You can calculate the time spent in each phase of the cell
cycle from the percentage of cells in that stage
Number of Cells
Field 1
Field 2
Field 3
TOTAL
% of Total
(Pie Chart)
Time in each
stage
(% x 1,440min)
Interphase
1247
1820
1490
Prophase
67
88
101
Metaphase
39
67
53
Anaphase
26
36
45
Telophase
13
9
19
TOTAL
159
5120
3.1%
44.6 min