Transcript The Cell Cycle: Cell Growth, Cell Division

The Cell Cycle:
Cell Growth, Cell
Division
Where it all began…
You started as a cell smaller than
a period at the end of a sentence…
And now look at
you…
How did you
get from there
to here?
Why do cells divide?
• Reproduction
– asexual reproduction
• one-celled organisms
• Growth and
Development
– from fertilized egg to
multi-celled organism
• Repair and
Replacement
– replace cells that die
from normal wear & tear
or from injury
amoeba
Cell Cycle
M
Mitosis
Cell cycle
G2
Gap 2
• Cell has a “life cycle”
cell is formed from
a mitotic division
cell grows & matures
to divide again
G1, S, G2, M
epithelial cells,
blood cells,
stem cells
S
Synthesis
cell grows & matures
to never divide again
liver cells
G1G0
brain / nerve cells
muscle cells
G1
Gap 1
G0
Resting
Interphase
• 90% of cell life cycle
– cell doing its “everyday job”
• produce RNA, synthesize proteins/enzymes
– prepares for duplication if triggered
I’m working here!
Time to divide
& multiply!
Interphase
• Divided into 3 phases:
– G1 = 1st Gap
• cell doing its “everyday job”
• cell grows
• A few hours to indefinitely
– S = DNA Synthesis
• copies chromosomes
• 3-6 hours
– G2 = 2nd Gap
• prepares for division
• cell grows (more)
• produces organelles,
proteins, membranes
• 2-5 hours
G0
green = key features
Interphase
• Longest phase of the
cell cycle
– Consists of G1, S, G2
• Cell prepares for
mitosis
– replicates chromosome
• DNA & proteins
– produces proteins &
organelles
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Organizing DNA
• DNA is organized in
Nucleosomes
DNA
histones
– double helix DNA molecule
– wrapped around Histones
• like thread on spools
– DNA-protein complex =
Chromatin
• organized into long thin fiber
chromatin
– condensed further during
mitosis
double stranded chromosome
duplicated mitotic chromosome
Copying DNA & packaging it…
• After DNA duplication, chromatin condenses
– coiling & folding to make a smaller package
mitotic chromosome
DNA
chromatin
doublestranded
mitotic human
chromosomes
Mitotic Chromosome
• Duplicated chromosome
– 2 chromatids
– narrow at centromere
– contain identical
copies of original DNA
homologous
chromosomes
homologous
chromosomes
single-stranded
sister chromatids
double-stranded
homologous = “same information”
Mitosis
• Dividing cell’s DNA between
2 daughter nuclei
– “dance of the chromosomes”
• 4 phases
– Prophase
– Metaphase
– Anaphase
– Telophase
Mitosis
Overview of mitosis
interphase
prophase
I.P.M.A.T.
(pro-metaphase)
cytokinesis
metaphase
anaphase
telophase
green = key features
Prophase
• Chromatin condenses
– Becomes chromosomes
• chromatids
• Centrioles move to opposite
poles of cell
– animal cell
• Protein fibers cross cell to form
mitotic spindle
– microtubules
• actin, myosin
– coordinates movement of
chromosomes
• Nucleolus disappears
green = key features
Transition to Metaphase
• Prometaphase
– Special proteins attach
to the centromeres
• creating kinetochores
– microtubules attach at
kinetochores
• connect centromeres to
centrioles
– Nuclear envelope
fragments
green = key features
Anaphase
• Sister chromatids separate
– move to opposite poles
– pulled at centromeres
– pulled by motor proteins
“walking”along microtubules
• actin, myosin
• increased production of
ATP by mitochondria
• Poles move farther apart
– polar microtubules lengthen
green = key features
Telophase
• Chromosomes arrive at
opposite poles
– Nuclear envelop starts to
reappear
– nucleoli form
– Chromosomes uncoil
• no longer visible under light
microscope
• Spindle fibers disperse
• Cytokinesis
– cell division
Cytokinesis
• Animals
– constriction belt of actin
microfilaments around
equator of cell
• cleavage furrow forms
• splits cell in two
• like tightening a draw
string
Mitosis in whitefish blastula
Cytokinesis in Plants
• Plants
– Cell Plate
• vesicles line up at
equator
– derived from Golgi
• vesicles fuse to form 2
cell membranes
– new cell wall laid
down between
membranes
• new cell wall fuses with
existing cell wall
Cytokinesis in plant cell
onion root tip
G1/S checkpoint
• G1/S checkpoint is most critical
– primary decision point
• “Go Ahead signal”
– if cell receives “GO” signal, it divides
• internal signals: cell growth (size), cell nutrition
• external signals: “growth factors”
– if cell does not receive
signal, it exits cycle &
switches to G0 phase
• non-dividing, working state
What about Stem cells?
• What are stem cells?
• How can they be used?
• What are concerns about using stem
cells?
• What are the types of stem cells?
Multicellular organisms depend on
interactions among different cell types.
CELL
TISSUE
leaf
stem
vascular
tissue
ORGAN
lateral
roots
primary
root
shoot system
SYSTEMS
root system
• Tissues are groups of cells that
perform a similar function.
• Organs are groups of tissues that
perform a specific or related function.
• Organ systems are groups of organs
that carry out similar functions.
Specialized cells perform specific
functions.
• Cells develop into their mature forms through the
process of cell differentiation.
• Cells differ because different combinations of genes
are expressed.
• A cell’s location in an embryo helps determine how it
will differentiate.
Outer: skin cells
Middle: bone cells
Inner: intestines
Stem cells can develop into different
cell types.
• Stem cells have the ability to
– divide and renew themselves
– remain undifferentiated in form
– develop into a variety of specialized cell
types
• Stem cells are classified into three types.
– totipotent, or growing into any other cell type
– pluripotent, or growing into any cell type but a
totipotent cell
– multipotent, or growing into cells of a closely related
cell family
• Stem cells come from adults and
embryos.
– Adult stem cells can be hard to isolate and grow.
– The use of adult stem cells may prevent transplant
rejection.
– The use of embryonic
stem cells raises
ethical issues.
– Embryonic stem cells
are pluripotent and
can be grown indefinitely
in culture.
First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming
an inner cell mass. These cells are then removed and grown with nutrients.
Scientists try to control how the cells specialize by adding or removing certain
molecules.
• The use of stem cells offers many current
and potential benefits.
– Stem cells are used to treat leukemia and lymphoma.
– Stem cells may cure disease or replace damaged
organs.
– Stem cells & Blindness
– Stem cells may revolutionize the drug development
process.