The Cell Cycle
Your cells are dividing…
• You need new cells for:
– replacing all of the cells that are dying.
– Repairing injury
– New growth (getting taller/wider)
• Facts:
• You replace all of your skin every 27
days.
• 300 million cells in your body die and
must be replaced every minute.
50,000 of the cells in your body will
die and be replaced with new cells,
all while you have been reading this
sentence!
From beginning to end…
• The cell cycle begins when the cell is
formed
• Cell grows increase cytoplasm till it
can’t hold anymore….or else…
• The cycle ends when the cell divides
and forms new cells.
Before cells divide…
1) Before a cell can divide it must make
an extra copy its DNA.
2) This is called Replication
-DNA (deoxyribonucleic acid) contains all
the information that tells the cell how to
make proteins.
DNA REPLICATION
• The DNA is normally long and
stringy.(chromatin)
•
The cell winds up the DNA into
chromosomes (chromosome shape of an X).
• The cell has to an entire copy the DNA so
that each new cell will have an identical copy
of the DNA.
Chromosome Numbers
• Number of chromosomes has nothing to do
with the complexity of organisms.
• Example: Fruit Flies have 8 chromosomes,
potatoes have 48 chromosomes, humans
have 46 chromosomes, a single cell protozoa
1600, chickens have 78.
• For human we have 46 chromosomes (23
pairs) During Replication the number doubles
to 92.
Making More Prokaryotic Cells
• Bacteria undergo binary fission
• Binary fission is a type of asexual
reproduction.
• Binary fission copies the circular DNA
and results in two cells that are equal in
size.
Eukaryotic Cells and DNA
• Eukaryotes are usually much larger and
more complex than prokaryotic cells.
• The number of chromosomes in the
cells of eukaryotes differ depending on
the organism
Human Chromosomes
• Humans have.. 46
chromosomes
• Each pair are made
23 homologous
chromosomes pairs.
Karyotype Chromosome Map
Making More Eukaryotic Cells
• Stage 1: Starts just after division
– cytoplasm grows
– toward the end the DNA condense
and makes an extra copy. (replication)
• The two copies are called sister
chromatids.
• Chromosomes are held together at
the centromere. (in the center)
Connects all 2 sister chromatids.
Making More Eukaryotic Cells
• Stage 2: The chromatids separate in a
process called mitosis.
• Mitosis ensures that each new cell
receives a copy of each chromosome.
Stages of Mitosis
•
•
•
•
•
•
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Interphase
• Before mitosis begins…
– The cell grows (cytoplasm)
– the chromosomes are
replicated (copied).
• Each chromosome now
consists of two chromatids.
Prophase
• The nuclear envelope
breaks apart
• Chromosomes
condense to rod-like
structures (like an X).
• The centrioles move
to opposite sides of
the cell
• spindle fibers form
between centrioles.
Metaphase
• Chromosomes line
up along the equator
(middle) of the cell.
• Each chromosome
attaches to a spindle
fiber.
Anaphase
• The chromatids
separate
• Chromatids are
pulled to opposite
sides of the cell by
the fibers attached
to the centrioles.
Telophase
• The nuclear
membrane forms
around the two
sets of
chromosomes
• Chromosomes
unwind, the fibers
disappear.
• mitosis is
complete.
Cytokinesis
• In plant cells, a cell
plate forms between
the two cells (this is
will become the cell
wall)
• In animal cells a
cleavage furrow
forms as the two
cells pinch apart.
Cleavage furrow
Cell Plate
Cytokinesis
• Once mitosis is completed, the cytoplasm splits
in tow.
• This results in two identical cells that are also
identical to the original cell from which they
were formed.
• After cytokenesis, the cell cycle is complete and
they will begin the cell cycle again.
Stages of Mitosis
http://www.sep.alquds.edu/biology/scripts/Biology_english/part_3_4_files/image010.jpg
Significance of Cell Division
(mitosis and fission)
• Produces 2 cells that are genetically
identical to the parent cell.
• In unicellular organisms is asexual
reproduction.
• In multicellular organisms:
-Primarily--growth and repair
How are Mitosis and Binary
Fission Different? Binary
Fission is…
• Is not mitosis (no phases).
• Has no spindle fibers or microtubules of
any kind.
• The DNA does not condense into a
distinct chromosome