Transcript Cell Growth and Division

Cell Growth
and Division
How would you describe the
process by which a multicellular
organism increases its size?
Why do cells stay small?
Objectives
Explain the problems that growth causes
for cells.
Describe how cell division solves the
problems of cell growth.
Limits to Cell Growth
The larger a cell becomes, the more
demands the cell places on its DNA and
the more trouble the cell has moving
enough nutrients and wastes across the
cell membrane.
Two reasons why cell size is limited:
– If a cell were to grow without control,
DNA overload would occur.
– Rate of material exchange is dependent
on surface area
http://www.youtube.com/watch?v=xuG4ZZ1GbzI
Exchanging Materials
Food, oxygen and
water enter the cell
through the cell
membrane. Waste
products leave the
same way.
The rate at which this
exchange takes place
depends on surface
area (the total area of
its cell membrane)
Ratio of surface area to volume
As the length of a cell increases, its
volume increases faster than its surface
area.
The resulting decrease in the cell’s
surface-area-to-volume ratio makes it
more difficult for the cell to move needed
materials in and waste products out.
Cell Division
Before a cell
becomes too
large, it divides
into two daughter
cells by a
process called
cell division.
What are Chromosomes?
Chromosomes are
made up of DNA
DNA carries the cell’s
genetic code
The cells of every
organism have a
specific number of
chromosomes.
Uncoiled DNA
DNA Coils into Chromosomes
The structure of a chromosome
Chromatin
Chromatid
Centromere
Chromosomes are not visible in most cells
except during cell division.
At the beginning of cell division the
chromosomes condense into compact,
visible structures that can be seen under a
light microscope.
The Chromosome
Chromosome: “X” shaped cell
structure that directs cell activities
and passes on traits to new cells.
Each identical strand of the
chromosome is called a
chromatid.
The strands are held together by a
structure called the centromere.
Chromatin: Loosely coiled DNA
Parts of a Chromosome
The Cell Cycle
Interphase
– G1 Phase: Cell Growth
– S Phase: DNA Replication
– G2 Phase: Preparation for Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
The Phases
1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase
6. Cytokinesis
Links
http://www.cellsalive.com/mitosis.htm
http://www.cellsalive.com/cell_cycle.htm
Interphase: G1
Cell Grows
Synthesis of proteins
and new organelles
S-Phase
Chromosomes are
duplicated and the
synthesis of DNA
molecules takes
place.
G2 Phase
Many of the
organelles and
molecules required
for cell division are
produced.
The cell is then ready
to enter M-Phase to
begin the process of
Cell division
Prophase
The chromatin
condense into
chromosomes.
The centrioles
separate and a
spindle begins to
form.
The nuclear
membrane breaks
down.
Metaphase
The chromosomes line
up along the middle of
the cell.
“M”eet
in the
“M”iddle!
Each chromosome is
connected to a spindle
fiber at its centromere.
Anaphase
The sister chromatids
separate into
individual
chromosomes and
move apart.
Anaphase
pulled Apart
Telophase
The chromosomes
gather at opposite
ends of the cell and
lose their distinct
shapes.
Two new nuclear
membranes form
Two new Nuclei
Cytokinesis
The cell membrane
pinches the cytoplasm
in half.
Each daughter cell has
an identical set of
duplicate
chromosomes.
Plant Cells
Plant cells have a cell
plate that forms
between the two cells.
The cell wall is too
rigid to be pinched
apart.
Length of the Cell Cycle of a
Human Liver Cell
Interphase: 21 hours
Growth : 9 hours
DNA Replication: 10 hours
Preparation for Division: 2 hours
Mitosis: 1 hour
Prophase
Metaphase
Anaphase
Telophase
Uncontrolled Cell Growth
Cancer- a disorder in which some of the
body’s own cells lose the ability to control
growth.
Disease of the cell cycle
Summary Video