Download Ch. 10 Cell Growth and Division

Ch. 10 Cell Growth and
Division
Chapter 10 Outline
• 10-1: Cell Growth
– Limits to Cell Growth
– Division of the Cell
• 10-2: Cell Division
–
–
–
–
–
Chromosomes
The Cell Cycle
Events of the Cell Cycle
Mitosis
Cytokinesis
• 10-3: Regulating the Cell cycle
– Controls on Cell Division
– Cell Cycle Regulators
Limits to Cell Growth
•
There are two main reasons why cells
divide instead of grow indefinitely:
1. The larger a cell becomes the more
demands it places on the DNA
2. The Cell has more trouble moving enough
nutrients and wastes across the cell
membrane
•
There is only a finite amount of DNA in
a cell. If a cell grows larger, that same
amount of DNA has to support the entire
cell
Limits to Cell Growth
• The rate at which nutrients, water
and wastes move across the cell
membrane depends on the surface
area of the cell membrane. As a cell
grows larger, its volume increases
more than the surface area,
therefore, there isn’t enough surface
area (of plasma membrane) to
support the whole cell.
Cell Size Table
Cell Size
Surface Area
(length x width x 6)
Volume
(length x width x height)
Ratio of Surface Area
to Volume
Division of the Cell
• Before it becomes too large, a
growing cell will divide forming two
“daughter” cells. This process is
called Cell Division.
• Before cell division occurs, the cell
replicates (copies) its DNA so that
each of the two daughter cells will
have a full set of DNA.
Cell Division
• In prokaryotes, cell division is called
binary fission. Bacterial DNA is circular.
The DNA is copied and the cell splits in
two.
• In eukaryotes, much more preparation is
required because of the presence of
many pieces of DNA
– Two main stages of eukaryotic cell division:
• Mitosis – division of the nucleus
• Cytokinesis – Division of the cytoplasm
Cell Division (con’t)
• Mitosis is a type of asexual
reproduction since cells are
genetically identical to the parent
cell.
Chromosomes
• In eukaryotic cells, genetic information is
passed on from parent cells to daughter
cells in the form of chromosomes.
• Chromosomes are made up of DNA
(which carries the genetic code) and
proteins. Every organism has a unique
number of chromosomes. Humans have
46 chromosomes or 23 pairs.
Chromosomes (con’t)
• Chromosomes only form during cell
division. DNA normally exists in the cells
in a long, stringy form called chromatin.
When it is time for a cell to begin division,
the chromatin condenses and forms
tightly packed Chromosomes.
• Just before cell division, the DNA must
copy itself (so that each daughter cell
gets a full set of DNA).
Chromosome (con’t)
• Each side of a chromosome that has
already replicated is called a sister
chromatid. Sister chromatids are
identical. When a cell divides, sister
chromatids separate from each
other.
• Sister chromatids are attached to
each other in an area called the
centromere.
The Cell Cycle
• Cell Cycle:
– The series of events that cells go
through as they grow and divide.
• During the cell cycle, a cell grows,
prepares for division, and divides to
form two daughter cells.
– The Two daughter cells then begin the
cycle again.
Cell Cycle (con’t)
• Phases of the Cell Cycle
– M phase
• Mitosis
• Cytokinesis
– Interphase
• G1 phase
• S phase
• G2 phase
Events of the Cell Cycle
• Which phase is longer?
– Interphase is very long, but mitosis and
cytokinesis take place quickly.
– G1 phase:
• Cells are growing, making new proteins and
organelles
– S (synthesis) phase:
• Chromosomes are replicated
– G2 phase:
• More growth, more organelles made to prepare for
cell division
Mitosis
• Mitosis is divided into four phases:
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
• Prophase: longest phase
– Chromosomes form
– Centrioles separate (centrioles lie near the nuclear
envelope and help organize the fanlike structure called
the spindle which help separate the chromosomes)
– Chromosomes attach to fibers in spindle
– Nucleolus and nuclear envelope disappear
Mitosis (con’t)
• Metaphase
– Chromosomes line up at the equator or
middle of the cell
• Anaphase
– Sister chromatids separate and
become individual chromosomes
– Chromosomes move to opposite sides
of the cell
Mitosis (con’t)
• Telophase
– Chromosomes unwind
– Nuclear envelope reforms around each
set of chromosomes
– Spindle breaks apart
– Nucleolus reappears
• After the NUCLEAR division is
complete, the cell still must divide.
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Section 10-2
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Interphase
Centromere
Chromosomes
(paired chromatids)
Prophase
Cytokinesis
Spindle
Centriole
Telophase
Nuclear
envelope
reforming
Centriole
Individual
chromosomes
Anaphase
Metaphase
Cytokinesis
• The process of cytoplasm dividing
can happen in two ways :
– Animal cells: cell membrane is drawn
inward (cleavage furrow ) until the
cytoplasm is pinched into two parts
– Plant cells: cell plate forms midway
between the divided nuclei. The cell
plate gradually develops into a
separating membrane and a cell wall
forms there.
THE CELL CYCLE
G1 phase
M phase
S phase
G2 phase
Controls on Cell Division
• Cells stop growing when they come in
contact with other cells
– Ex: If you put some cells on a Petri dish with
nutrient broth in it, they will divide until they
cover the whole Petri dish.
Cell Cycle Regulators
• For many years, scientists searched for a
substance that regulates the cell cycle. In
1980, that substance was identified and
named cyclin.
– Cyclin is a protein that regulates the timing of
the cell cycle in eukaryotic cells
• Many other proteins have since been
discovered that help regulate the cycle.
Effects of Cyclin
The sample is injected
into a second cell in G2
of interphase.
A sample of
cytoplasm
is removed
from a cell
in mitosis.
As a result, the second
cell enters mitosis.
Cell Cycle Regulators
•
Two types of regulatory proteins:
1. Internal regulators:
– Respond to events inside the cell
– Allow the cell cycle to proceed only after
certain processes happen inside the cell
2. External regulators:
– Respond to events outside the cell
– Direct cells to speed up or slow down the
cycle
– Ex. Growth Factors
Uncontrolled Cell Growth
• Cancer:
– A 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 growth of most cells
– They form masses of cells called tumors.
Cells in tumors can break free and spread
throughout the body.
• Causes of Cancer
– Smoking
– Radiation exposure
– Viral infection