Transcript Cell Division

Cell Growth and Division
The Cell Cycle & Mitosis
Why do cells divide???
• DNA can only manage the contents of a
small cell.
• The cell can’t move food/wastes across a
membrane of a large cell
– As a cell gets bigger, its volume increases
faster than its surface area.
Why can’t cells grow forever?
• REASON 1: Not enough DNA!...as the
cell increases in size, it keeps the same
amount of DNA. Eventually the cell will
grow too much for the DNA to control all
its activities
Memory Trick: Think of DNA like a library
of books. If a town (cell) is too big, people
may have to wait for books!
Why Can’t Cells Grow Forever?
• REASON #2: Surface area of membrane
doesn’t increase as quickly as cell volume
Too little membrane  not enough
exchange of materials in and out of the
cell
Cell Division or Mitosis
• Before a cell gets too
big, it splits into
daughter cells.
• The two daughter
cells are identical to
each other (they’re
like twins!)
Cell Division in Prokaryotes
• DNA is copied and divided into
two cells
• Creates two identical daughter
cells
• Process is called Binary Fission
Cell Division in Eukaryotes
• DNA is found in
the nucleus
• Chromatin is DNA
& protein threads
that coil into
chromosomes
during cell
division.
Cell Division in Eukaryotes: The
Cell Cycle
• Cell Cycle: The series of
events that cells go
through as they grow and
divide.
• G1 Phase: cell
grows/makes new
proteins and organelles
• S Phase: DNA copied
The Cell Cycle
• G2 Phase:
Organelles/molecules
for cell division are
made
• M Phase (Mitosis):
Cell divides into 2
daughter cells
Structure of Chromosomes
• Coiled threads of DNA and proteins.
• Contains genes (hereditary information)
• Must successfully divide for new cells to
be made
Structure of Chromosome
Chromatids: 2 identical
copies
Of DNA that are
connected to
Form a chromosome
Centromere: the area
where chromatids are
attached (usually at the
middle of the chromatids)
• Basic Definitions
– Centromere
– Chromosome
– Chromatid
Chromosome #’s
• The cells of every organism have a
specific number of chromosomes
Cell Type
# of Chromosomes
Fruit Flies
8
Carrots
18
Human
46
Diploid vs. Haploid Cells
• Diploid Cells (2n) = 2 sets
of chromosomes…one from
each parent (Example:
human body cell)
• Haploid Cells (n)= only
have 1 set of chromosomes
(Example: Sperm or Egg
Cell)
Types of Chromosomes
• Sex chromosomes =
determine the sex of
an organism; either X
or Y
• Autosomes = all the
other chromosomes in
an organism
Cell Cycle
•
•
•
The series of events that cells go through as
the grow and divide
During the cycle, a cell grows, prepares for
division, and divides to form 2 daughter cells,
each of which then begins the cycle again
2 Main Parts
1) Interphase
2) Cell Division
Interphase
• Time between
divisions where cell
grows and replicates
DNA
• 3 Parts
1) G1 = cell grows
and matures
2) S = DNA is
copied
3) G2 = cell
http://www.cellsalive.com/cell_cycle.htm
prepares for
division
Before Mitosis
• Interphase (includes G1, S and G2) = Time
between divisions where cell grows and
replicates DNA.
Mitosis
• This involves division of the
nucleus
• 4 Phases
1) Prophase
2) Metaphase
3) Anaphase
4) Telophase
The Steps of Mitosis
• Prophase=
– Coiling of DNA into chromosomes
– Nuclear membrane breaks down
– Spindle forms
What is the spindle?
• 2 Structures located in the
cytoplasm called centrioles
move towards opposite sides
of the nucleus
• Microtubules (protein tubes)
called spindle fibers grow from
the centrioles
• Spindle fibers attach to
chromosomes at the
centromere and help pull
chromatids apart
The Steps of Mitosis
• Metaphase = Spindle fibers move
chromosomes to the center of the dividing
cell.
The Steps of Mitosis
• Anaphase = Chromatids of each
chromosome separate at the centromere
and move toward opposite poles of the
dividing cell
The Steps of Mitosis
• Telophase =
–
–
–
–
Chromosomes reach poles of cell
Spindle breaks down
Chromosomes uncoil into chromatin
Nuclear envelopes and 2 nucleoli form
The Steps of Mitosis
• Cytokinesis= Division of the cytoplasm
– Animal Cell: Cleavage Furrow (cell
membrane pinches in )
The Steps of Mitosis
• Cytokinesis = Division of the cytoplasm
– Plant Cell: Cell Plate (cell wall grows
between daughter cells)
Mitosis in Real Cells
http://www.cellsaliv
e.com/mitosis.htm
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Life Spans of Human Cells
Cell Type
Life Span
Cell Division
Esophagus Lining
2-3 Days
Yes
Sm. Intestine Lining
1-2 Days
Yes
Lg. Intestine Lining
6 Days
Yes
120 Days
No
10 Days – Decades
Many don’t
Heart Muscle
Long Time
No
Skeletal Muscle
Long Time
No
Nerve Cells
Long Time
No
Red Blood Cells
White Blood Cells
Questions to think about…
• White blood cells help protect the body
from infection/disease. How might their
function relate to their life span?
– 10 hrs: common everyday germ
– 40 years: These cells recognize some
bacteria/viruses your whole life and kill them
Questions to think about…
• Based on the data, how are the
consequences of injuries to the spine and
heart similar to each other?
– Can’t make new cells
– Permanent damage
Questions to think about…
• Suggest a hypothesis that explains the life
spans of the lining of the esophagus, small
intestine and large intestine.
– Acid kills some cells
– A lot of food passes thru them
– Cells are easily damaged
Questions to think about…
• Cancer is a disease related to cell life
span and cell division. If cancer were
added to the data table, predict what
would be written under the columns “Life
Span” and “Cell Division”
– Life Span: long
– Cell Division: rapid