Download before cell division

Chapter 10
Cell Growth and Division
Cell Reproduction
Why do cells Reproduce?
To help tissues and organs grow and to replace dead or
damaged cells
Cells need to divide to limit their size because….
Their ability to exchange substances is limited by their surface area to
volume ratio. Small cell exchange substances more efficiently than large
cells.
Large cells need to make more protein to support cell functions. DNA can
not be copied quickly enough in large cells to support their needs.
Chromosomes
DNA is organized and packaged into structures call
Chromosomes in eukaryotic cells. Prokaryotic cells have a
loop of DNA.
Chromosomes
Are made of
Chromatin
Which is made of
Nucleosomes
Which are
DNA wound around Histones
Chromosome
Nucleosomes
(DNA wound around histones)
DNA
Chromatin
Chromatin
nucleus
UNPACKED
(before cell division)
PACKED Condensed package
During cell division
Chromosome
Preparing for Cell Division
All new cell come from the division of preexisting cells
Before a cell divides, it must copy its DNA
so that the original cell and its copy
(daughter cell) each has the DNA it needs to
carry out cell functions.
Cell Cycle
The cell cycle is a repeating sequence of
cellular growth and division during the life of
a cell
Interphase
Mitosis
G1
Prophase
S
Metaphase
G2
Anaphase
Telophase
Interphase
Cells that divide often
spend less time in
interphase, while
those that seldom
divide spend a long
time in interphase.
Which cells, brain or
bone, spend a longer
time in interphase?
Interphase
G1 (Growth)
Cell rapidly grows and makes more organelles
Cells that don’t divide remain at this stage
S (DNA synthesis)
A cell’s DNA is copied
G2 (Growth and preparation for division)
Cells continue to grow and develop special structures
(microtubules or spindle fibers) for cell division
Mitosis
The process of dividing a cell into two daughter nuclei
Following mitosis a process called cytokinesis occurs
in which the organelles and cytoplasm in the cell are
separated creating two new daughter cells.
Prophase
Chromosomes begin to
condense and become
visible under a light
microscope.
The nuclear membrane
breaks down.
The spindle forms
Metaphase
Chromosomes line up
at the cell’s equator.
Spindle fibers form a
link between the
centromeres of the
chromosome and the
poles of the cell.
Anaphase
The spindle fibers
shorten
Sister chromatids
move toward opposite
poles of the cell
Telophase
A nuclear envelope
forms around the
chromosomes at each
pole
Chromosomes uncoil
Spindle fibers
breakdown and
disappear
Cytokinesis
Cell membrane grows into the center of the cell
Nuclear membrane forms around the two new nuclei
Identify the Stages
Cell Cycle Regulation
Cell growth and division depend on protein
signals and other environmental agents.
Other things that regulate cell growth and
division:
Signals from surrounding cells and tissues
Availability of nutrients
Checkpoints
G1 Checkpoint
Before a cell can go into the S phase (DNA
replication) The health and size of the cell is
evaluated. If conditions are not favorable, the
cell goes into a resting period.
G2 Checkpoint
Before a cell can begin mitosis, its DNA needs
to be examined for mistakes. Enzymes correct
mistakes so that each daughter cell produced in
mitosis contain the same DNA. Cell size is also
double checked.
Checkpoints cont.
Mitosis checkpoint
During metaphase, the cell checks to see if the
chromosomes are properly attached to the
spindle fibers.
Cancer
Uncontrolled cell growth and division can result in
masses of cells that invade and destroy healthy
tissues.
 Cancer results from the loss of control of cell
cycle regulation
 Benign tumors or malignant tumors may occur.
 Chemotherapy or radiation is used to kill cancer
cells
 Some cancers can be prevented by avoiding
those things known to cause cancer.