Download File - Down the Rabbit Hole

THE CELL CYCLE
WHY CELLS DIVIDE
WHAT DO ALL CELLS
REQUIRE TO SURVIVE?
• A complete set of
genetic instructions
• Genetic instructions
are coded in the
DNA of cells
• Needed to produce
the required
molecules that drive
life functions
(metabolism)
CELL DIVISION
MITOSIS
• Results in genetically
identical daughter
cells
• Cells duplicate their
genome before they
divide
• Ensuring that each
daughter cell
receives an exact
copy of the genetic
material, DNA
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WHY DO CELLS DIVIDE?
• About 2 trillion cells are
produced by an adult
human every day.
• Cell division, or
reproduction occurs in
all organisms
• WHY?
• It depends on the cell
type and the organism
WHY DO CELLS DIVIDE?
ASEXUAL REPRODUCTION
• Growth
• Cells must divide to
maintain maximum
efficiency.
• Development
• Cells get old and
die and must be
replaced
• Repair
PROKARYOTE CELL DIVISION
BINARY FISSION
• Prokaryotic cells
have a circular
DNA molecule
attached to the
inner cell
membrane
• They divide
through a simple
form of division
called Binary
Fission
E. coli dividing by binary fission
PROKARYOTIC CELL DIVISION
• 3 step process
• DNA strand splits and
forms a duplicate of
itself.
• The two copies move
to opposite sides of the
cell
• Cell membrane forms
between two new and
identical cells.
EUKARYOTIC CELLS
CHROMOSOMES
• 1,000 times more DNA then
an average prokaryotic
cell.
• Organized into several
linear chromosomes.
• Organization is much more
complex than the single,
circular DNA molecule in a
prokaryotic cell
Figure 12.3
50 µm
CHROMOSOMES
• All eukaryotic cells store
genetic information in
chromosomes.
• Most eukaryotes have
between 10 and 50
chromosomes in their
body cells.
• Human cells have 46
chromosomes.
• 23 pairs
STRUCTURE OF CHROMOSOMES
• Complex of DNA and
protein called
chromatin
• Condenses during cell
division
• DNA exists as a single,
long, double-stranded
fiber
• Organized in coils
• DNA is wrapped around
proteins called histones.
THE CELL CYCLE
• Some cells divide
constantly:
• cells in the embryo,
skin cells, gut lining
cells, etc.
• Other cells divide
rarely or never: only
to replace
themselves.
• Actively dividing cells
go through a cycle: a
repeating sequence
of cellular growth and
division.
THE CELL CYCLE
•There are 4 stages
•G1
•S
•G2
•Mitosis
THE CELL CYCLE
• The first 3 phases are
•
•
collectively called Interphase
The G1 phase
• Most time spent
• Growth and normal function.
• Control of cell division.
The S or Synthesis phase
• DNA is replicated.
• The chromosome goes from
having one chromatid to two.
• G2 phase
• Cell prepares for mitosis
• Amount of cytoplasm
(including organelles)
increases in preparation for
division
CHROMOSOME REPLICATION
(S-PHASE)
• Each condensed chromosome consists of 2 identical
chromatids joined by a centromere.
Non-sister
chromatids
Centromere
Duplication
Sister
chromatids
Two unduplicated
chromosomes
Sister
chromatids
Two duplicated chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CHROMOSOME REPLICATION
A packaged
chromosome
Chromatid
Chromosome arm
Centromere
Identical chromatid
• During the S
Replication
phase of the
cell cycle,
DNA
replicates.
Chromosome arm
Replication Animation:
http://www.johnkyrk.com/DNArepl
ication.html
INTERPHASE SUMMARY
•
•
•
•
•
•
•
Normal
function
ATP is synthesized.
Damaged parts
are repaired.
Wastes are
excreted.
Proteins are
made.
Organelles are
formed.
Specialized tasks
are performed.
Some cells stay in
Interphase all of their
lives!
MITOSIS
FOURTH PHASE OF THE CELL CYCLE



Mitosis is normal cell
division
The process by
which the nucleus
of a cell divides to
form two new
nuclei
Mitosis has 4 phases
MITOSIS
• Prophase
• Metaphase
• Anaphase
• Telophase
REMEMBER!!!!!
Prophase
Metaphase
Anaphase
Telophase
PMAT
PROPHASE
•
•
•
•
Chromatin
condenses and
chromosomes
become visible
Nuclear membrane
disappears.
Centrioles migrate
to opposite sides
apparently
propelled by the
lengthening of
microtubules
Mitotic spindle
begins to form
Centrioles
METAPHASE
•
•
•
•
•
Metaphase is the
longest stage of
mitosis, lasting about
20 minutes.
The centrosomes are
now at opposite ends
of the cell.
Chromatids migrate
to equator of spindle.
Spindle fibres attach
to the chromatids.
The entire apparatus
of microtubules is
called the spindle
because of its shape.
ANAPHASE
• Anaphase is the shortest
stage of mitosis, lasting
only a few minutes.
• Anaphase begins when
the sister chromatids of
each pair suddenly part.
• Each chromatid thus
becomes a full-fledged
chromosome.
• The chromosomes begin
moving toward opposite
ends of the cell, as
microtubules shorten.
ANAPHASE
• The cell elongates as
structural microtubules
lengthen.
• By the end of
anaphase, the two
ends of the cell have an
equal and complete
collection of
chromosomes.
• Chromatids are now
called chromosomes.
ANAPHASE
Daughter
chromosomes
TELOPHASE
• Cytoplasm divides: cytokinesis
• Nuclear membrane reappears. There are now
two nuclei.
• Chromosomes uncoil (they are no longer visible)
and the DNA is now called chromatin
• Mitosis, the division of one nucleus into two
genetically identical nuclei, is now
complete.
TELOPHASE
THE DIFFERENCE IN PLANT AND ANIMAL CELLS
•
Plant Cells
•
The Golgi body
forms a cell plate
between the two
nuclei.
•
The plasma
membrane reforms
on each side of the
plate which grows
outward becoming
the new cell wall.
TELOPHASE
THE DIFFERENCE IN PLANT AND ANIMAL CELLS
•
Animal Cells
•
A cleavage appears
(groove) caused by a
contractile ring of actin
microfilaments
•
The contraction of
microfilaments is like the
pulling of drawstrings
•
The cell is pinched in
two
CYTOKINESIS
• Occurs during telophase,
generally at the same
time that the nuclear
membrane is reforming,
(yet they are distinct
processes.)
• The cytoplasm divides –
the organelles are equally
distributed between the
two daughter cells
• Two identical daughter
cells are formed.
Mother cell
STAGES OF MITOSIS
Nucleus with un-condensed chromosomes
Condensed chromosomes
Equator of the cell
Interphase
Poles of the cell
Disappearing
Prophase
nuclear
membrane
Mitotic
spindle
Two
daughter
cells
Metaphase
Anaphase
Telophase
REVIEW
How do little elephants grow up to be big elephants?
REVIEW
Why do animals shed their skin?
REVIEW
What happens when an organism is injured?
THREE REASONS WHY CELLS
REPRODUCE ASEXUALLY
• Growth
• Development
(replacement)
• Repair
Cancer = Uncontrolled Cell Growth