2. Humble Beginnings
Every living thing on
earth starts as a
single cell
3. All Cells Have a “Life Cycle”
• Includes periods of growth, rest & replication
• Can be short (minutes) or long (years)
• Different cell types have very different cycles
4. Cells Divide for Different Reasons
• To replace
old/worn out
cells (red blood
cells)
• To repair injured
tissues or
combat illness
• To reproduce
(create another
entire organism)
5. Three Types of Cell Division
Binary Fission
• Used by prokaryotes (unicellular: bacteria)
• Fast & simple: every 20 – 30 min.
Mitosis
• Used by eukaryotic, somatic cells (body)
• Much more complex
• Highly regulated
Meiosis
• Even more complicated (cells divide twice)
• Used by eukaryotic germ cells (reproductive)
6. Binary Fission in Prokaryotes
Bacteria only have 1 chromosome
• A single strand of DNA
• Circular in shape
7. Binary Fission in Prokaryotes
DNA duplicates
• Two circular DNA strands move apart
• Cell doubles in size
8. Binary Fission in Prokaryotes
DNA moves to opposite ends of cell
Cell membrane grows inward
Cell wall grows from membrane materials &
pinches cell in two
9. Binary Fission in Prokaryotes
Two new cells are formed
• Identical genetically (same DNA)
• Cytoplasm contents vary
10. Types of Cell Division
Binary Fission
• Used by prokaryotes (unicellular: bacteria)
• Fast & simple: every 20 – 30 min.
Mitosis
• Used by eukaryotic, somatic cells (body)
• Much more complex
• Highly regulated
Meiosis
• Even more complicated
• Used by eukaryotic germ cells (reproductive)
11. Cell Cycle in Eukaryotes
Interphase
• Longest stage
• 90% of cell’s life
• G - no division
0
• 3 checkpoints:
• G – gap 1
1
• S - synthesis
• G – gap 2
2
Mitosis
• 4 stages
• Cytokinesis completes
the cycle
12. Interphase – G1 (1st Gap or Growth phase)
Cell Growth
• Organelles replicate
• Cell volume doubles
Cell does its job
• Normal metabolic
processes
Longest phase
Some cells stay here
permanently
G1 checkpoint
• Is cell big enough?
• Environment good?
13. Interphase – S (Synthesis phase)
Chromosome
Replication
• Loose bundles of
chromatin
• All DNA in nucleus
copied resulting in…
• Two identical strands
of each chromosome
• Sister chromatids
joined by centromere
14. Interphase – G2 (2nd Gap or Growth phase)
More growth
• Cell volume
increases
G2 Checkpoint
• DNA mistakes?
• Cell volume OK?
• Environment
good?
Shortest phase
16. Mitosis - Prophase
DNA coils & condenses (like
thread on a spool) to form
distinct chromosomes
Nuclear membrane disappears
Spindle fibers form out of
centrosomes (2 centrioles ea.)
17. Metaphase
Spindle fibers attach to
kinetochores on the
centromeres
Chromosomes line up
at the equatorial plane
(middle) of the cell
Mitotic spindle
checkpoint
• Are all chromosomes
lined up?
• Are they all attached
to spindle fibers?
18. Anaphase
Spindle fibers shorten, pulling
sister chromatids apart
Chromatids are drawn to
opposite ends (poles) of the cell
Centromere connections are cut
19. Mitotic Spindle
Microtubules of the spindle
attach to kinetochores on
?
chromosomes
Sister chromatids are
pulled apart by
?
spindle fibers
Other unattached spindle
fibers push against one
another to elongate
(stretch out) the cell
20. Telophase
Chromosomes reach
the poles
New nuclear
membranes form
around chromatids
Chromosomes
unwind to become
thread-like chromatin
again
Nucleolus forms
21. Cytokinesis
The cytoplasm is
evenly divided
New cell membrane
forms in animal cells
New cell wall is built
across for plant cells
22. Cytokinesis in Animal Cells
Microfilaments assemble around cell middle
Actin& myosin
microfilaments
form a ring
around cell
ATP (energy)
used to
squeeze cell
in half
23. Cytokinesis in Plant Cells
Rigid cell wall can’t just be squeezed in half
Golgi apparatus sends
vesicles filled with cell
wall building materials
to center
Cell plate forms at
equatorial plane
Cell wall fills in gaps,
cleaves cell in two
24. Interphase – G0 (pre-growth or resting phase)
Mitosiscreates two
identical daughter
cells that go on to
enter Interphase
• Some enter G 1 and
divide again
• Some enter G0 - a
rest phase where
they do their job
34. Cell Cycles vary by Type of Cell
Nerve, liver & muscle cells
• Most stay in G0 (never divide)
• Some divide only after years, if
there are injuries
• Brain & spinal chord injuries are
often permanent because of this
Skin, hair, eye, cheek
& intestinal lining cells
• Exposed to more wear
& tear than other cells
• Replaced every 1 - 35
Red blood cells (hemoglobin)
days
• Most rapidly dividing • Formed from bone marrow stem cells
cells in humans • Never divide once formed
• Die & replaced after ~ 4 months
35. Cancer - Cell Cycle out of Control
Cancer cells
• Tumors result from rapid, out of
control cells dividing
• Bypass normal G1, G2 and/or mitotic
spindle checkpoints
• Sloppy cell division = big trouble
Lack of quality controls
• More mutations
• Disorganized/deformed cells
• Signal proteins lost/changed
• Contact inhibition lost
36. Your Turn…
What is binary fission? What type of cells
use this process?
Draw and label the cell cycle…include G1,
S, G2, M and cytokinesis…what happens at
each stage?
What are the stages of Mitosis?
What disease is associated with unregulated
mitosis?
Notes de l'éditeur
Erythrocytes have no nucleus, are made in the red marrow of bones, and live about 120 days. As red blood cells wear out in the bloodstream, they are taken in by the spleen, an organ on the left side of the abdomen below the stomach, and destroyed. Parts of the old cells are salvaged to make new red blood cells. Skin cells are dividing every day (about once every 20 hours). Embryonic human cells divide about once a day (in the early stages of development). Some nerve cells never divide after being formed in an embryo, which means they live as long as you do!
Who has heard of Mitosis – Meiosis?
Toddler/childhood phase of rapid growth and activity
Puberty phase - getting ready for reproduction
Tubulin proteins are formed which will make up the spindle, organelles are replicated, energy is stored up, and cytosol increases in volume