Download Chapter 10 – Cell Growth and Division

Chapter 10 – Cell Growth and Division
10-1 Cell Growth
When a living thing grows, what happens to its cells? Do cells
increase in size or are there just more cells?
Answer: just more cells
Limits to Cell Growth
1. DNA “overload”
-remember DNA contains the info that controls a cell’s function
-the larger a cell becomes, the more demand
the cell places on its DNA
-Eukaryotes: DNA stored in nucleus
-small cell: info stored in that DNA is able to
meet all cell’s needs
-larger cell: usually doesn’t make extra
copies of DNA
-growth w/o limit = “information crisis”
-can’t serve increasing needs of the
growing cell
2. Exchanging Materials
-trouble moving enough nutrients and
wastes across cell membrane
-remember, the cell membrane regulates what enters and leaves
the cell
enters: food, water, oxygen
leaves: waste products
-rate of exchange between food, water, oxygen entering and
waste leaving depends on surface area
-rate which food and oxygen are used up and waste is produced
depends on volume
-depends on surface area to volume ratio
-cells must divide as they grow!
1
Ratio of Surface Area to Volume
*SA= length x width x # sides
*V= length x width x height
Ratio of the above looks like the following;
SA : V
ex: 2:1 or 3:1
Volume increases faster than SA,
causes SA to V ratio to decrease
=serious problems for cell
If cell gets too large:
-difficult to get oxygen and nutrients in
and wastes out
****That’s the reason why cells do not
grow much larger even if the organism of
which they are a part does.****
If cells can only get so large, then how do cells
(and organisms-which are made of cells) grow?
Cell Division
-process which cells divides into 2 new
“daughter” cells
-before division occurs the cell replicates (or
copies) all of its DNA
-solves the problems:
-info storage because each daughter
cell gets 1 complete set of genetic
information
2
-SA:V- each daughter cell has
increase SA to V ratio
-allows sufficient exchange of
materials with the environment
STOP
10-2 Cell Division
Prokaryotic Cell Division: separate cell contents
into 2 parts
Eukaryotic Cell Division: 2 Main Stages
1. Mitosis-division of nucleus
2. Cytokinesis- division of cytoplasm
Chromosomes
-carries the genetic info
-made up of DNA and proteins
-DNA carries coded genetic information
-every organism has specific # of chromosomes
humans: 46 fruit flies: 8
carrot cells: 18
Chromosomes are not visible except during cell division
because the DNA and protein molecules are spread
throughout the nucleus
During the cell cycle, a cell grows, prepares for
division and divides into 2 daughter cells
Interphase is divided into 3 phases: G1, S and G2
*G1: size of the cell increases and it makes
new proteins and organelles
*S: copying of chromosomes takes place
[
3
*G2: Many of the organelles and molecules
needed for cell division are produced
M phase, or cell division
-includes mitosis and cytokinesis
Mitosis is divided into 4 phases:
1. Prophase
-Chromosomes condense and become
visible
-The nuclear envelope breaks down
2. Metaphase
-Chromosomes line up across the center
of the cell
3. Anaphase
-The 2 sets of chromosomes move apart
4. Telophase
-Chromosomes move to opposite ends
of the cell
-Cells lose their distinct shape and 2
nuclear envelopes form
Cytokinesis
-usually occurs at the same time a
telophase
-cell membrane pinches the cytoplasm
into 2 nearly equal parts
-In plant cells, a cell plate forms midway between
divided nuclei and a new cell wall begins to form
in the cell plate
4
10-3 Regulating the Cell Cycle
Controls on Cell Division
-most cells will grow until they come into contact with
another cell
-cell growth and division can be turned off and on
-Injury (cut in skin, break in bone)
-cells at edges are stimulated to divide rapidly, produces new cells, starts
healing process, when healing process nears end,rate of division slows
For many years, biologists searched for something that might regulate the cell
cycle-something that would tell the cell when it was time to divide, duplicate their
chromosomes or enter another phase of the cycle
1980’s- Scientists discovered that cells in mitosis contained a protein that when
injected into an nondividing cell would cause a mitotic spindle to form
They discovered the amount of this protein rose and fell in time with the cell cycle
Cyclins- family of proteins that regulate the timing of
the cell cycle in Eukaryotic cells
Internal Regulators
-respond inside cell
-only allow cell cycle to proceed when certain
processes have happened
Ex: -one regulatory protein makes sure cell doesn’t enter mitosis until all
its chromosomes have been replicated
-another prevents a cell from entering anaphase until all its
chromosomes are attached to the spindle
External Regulators
-respond to events outside the cell
-direct cells to speed up or slow down the cell
cycle
5
-ex: growth factors- important during embryonic development
and wound healing;-prevent excessive growth and keep the tissues of
the body from disrupting each other
Cancer- disorder in which some of the body’s own
cells lose the ability to control growth
-cancer cells do not respond to the signals that regulate the growth of
most cells
-divide uncontrollably
-form masses called tumors
-can damage surrounding tissues
-cells can break loose from tumors and spread
6