In This Lesson:
Mitosis and Cell
Cycle
(Lesson 2 of 3)
Today is Wednesday,
November 11th, 2015
Pre-Class:
So if everyone in this room started from one cell (the
zygote - remember?), how did we all get so big?
What’s that process called?
Also, take note of the homework.
Today’s Topics
• Cell Cycle
• Mitosis
• And maybe some rabbits…
http://sajjadzaidi.com/2007/jan/giant_bunnies_for_breakfast/
By the end of this lesson…
• You should be able to describe the cycle most
living cells go through in order to grow and
reproduce.
• You should be able to describe each of the
main steps in the mitosis process of cell
reproduction.
Where is this in my book?
• P. 129 and following…
Introducing this with a clip…
• …from a short film.
• i am so proud of you by Don Hertzfeldt (part of
the feature film It’s Such a Beautiful Day)
– Listen for the references to cells.
Aside: How Old are You?
• Like in the short film clip, your cells really do
get replaced every so often.
– Some can complete a cycle in a day; others, like
bacteria, can complete one on the scale of
minutes.
• What this means, however, is that you are
older than any of the cells you have right
now.
– Your oldest cells right now are only between 7 and
9 years old.
The Cell Cycle
• Cells have their own life cycles.
• Divided into five phases that form a repeating
loop:
– G1
–S
– G2
– Mitosis
– Cytokinesis
• Side note: The “G” stands for “Gap.”
The Cell Cycle
http://www.treatgene.com/wp-content/uploads/2009/10/cellcycle3.jpg
The Cell Cycle
• The Cell Cycle is really only 3 general
steps:
1. Interphase:
• G1
– The first growth phase.
• S phase
– Synthesis (DNA is copied - remember that?)
• G2
– The second growth phase.
– Nucleus prepared for division.
The Cell Cycle
2. Mitosis (sometimes called M phase):
– The cell nucleus divides.
• Chromosomes are separated.
3. Cytokinesis
– The cytoplasm/membrane divides.
The Cell Cycle
• One other note…
• Some cells, like some muscle cells, don’t really
divide.
– We say they are in G0 stage.
The Cell Cycle
• The cycle is regulated by proteins called
cyclins.
Interphase
http://www.treatgene.com/wp-content/uploads/2009/10/cellcycle3.jpg
Interphase Steps
• Checkpoints
– End of G1
– During G2
– End of Mitosis
• Checkpoints determine if the cell will go to the
next step.
• What happens if a checkpoint “breaks?”
Cancer
• Uncontrolled cell division leads to
some forms of cancer.
• This is how tumors form.
– A lot of cancer research is currently
directed toward fixing cyclin-related
problems.
– Other research is looking at…naked
mole rats.
• Article!
http://www.tc-cancer.com/images/img-cancer-cell.jpg
Causes of Cancer
• Many cancers originate when DNA
(chromosomes) is damaged.
– Things like UV radiation (tanning) and
smoking come to mind.
• Additionally, telomeres degrade.
– Telomeres are “caps” on the ends of
the chromosomes that are made of
junk DNA.
– With each cell division, however,
telomeres get smaller.
http://www.psychologytoday.com/files/u693/telomere.jpg
More on Telomeres
• In the 1960s, Leonard Hayflick
discovered that there was a limit
to how many times cells could
divide before their telomeres
were eroded completely away.
– That number is somewhere
between 52 and 60 times, and
it’s now called the Hayflick Limit.
• After that point, the cells may
either be told to die (apoptosis
– programmed cell death) or
simply won’t divide anymore.
http://www.nature.com/polopoly_fs/7.11184.1372152253!/image/Hayflick28.jpg_gen/derivatives/landscape_630/Hayflick28.jpg
Normally Functioning Checkpoints
• G1 Checkpoint:
– At the end of G1, if growth and original DNA is OK,
start copying DNA in S phase.
• G2 Checkpoint:
– Double-check that the DNA is OK, start mitosis.
• Mitosis Checkpoint:
– Exit mitosis, divide the cell, grow again.
Checkpoints
http://skreened.com/scienceforscientists/dna-checks-itself-before-it-wrecks-itself
The Time Scale (Generally)
http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect16.htm
Time for a kindagame…
• Grab yo’ laptops and find The Cell Cycle Game:
• http://nobelprize.org/educational/medicine/2001/in
dex.html
– Complete the Quia activity called Cell Cycle Game.
• Keep an eye on the dial in the upper left
corner and the “energy” in the upper right!
Healing
• So, do cuts heal faster on babies or old
people?
– Babies!
More hybrid animals!
• TED: Paul Wolpe – Questioning Bioengineering
Mitosis
• Mitosis is the process by which somatic cells
(body cells) replicate and divide.
– [technically it’s just the nucleus dividing, but
sometimes the names are used interchangeably]
• What do I mean by this?
– Start with one cell.
– Cell copies all its DNA/chromosomes.
• Chromosomes form an X-shape.
– Cell divides.
– Two daughter cells form.
And…the point?
• Why do mitosis?
– Growth
– Repair
– Differentiation (giving cells their jobs)
Chromosomes vs. Chromatids
S Phase
Chromosomes are
copied
Sister Sister
Chromosome
Chromosome
Chromatid
Chromatid
Pre-S Phase
Post-S Phase
Chromosome Vocabulary
• Chromatid
– Half of a duplicated (X-shaped) chromosome.
– Prior to duplication, it was called a chromosome.
• Sister Chromatids
– The two identical chromatid copies that make up
an X-shaped chromosome.
• Centromere
– The site at which the two sister chromatids join.
– Basically the same as the kinetochore.
Chromosome Structure
Sketch me!
Sketch me!
Sketch me!
Sketch me!
Sketch me!
Sketch me!
http://www.janewhitney.com/img/sister_chromatids.jpg
Mitosis
• What it looks like:
http://royaleb.files.wordpress.com/2009/04/mitosis_phases1.jpg
Mitosis
• What it kinda looks like:
http://www.geekosystem.com/wp-content/uploads/2010/07/donut-mitosis.jpeg
Mitosis
• What it does not look like:
http://icanhascheezburger.files.wordpress.com/2008/03/funny-pictures-mitosis-rabbits.jpg
The Steps of Mitosis
•
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
• Got a way to remember these?
Wait just a second…
• There’s a new organelle: the centriole.
– Small barrel-shaped structure.
– Comes from a region of the cytoplasm called the
centrosome.
– Produces spindle fibers.
• Like ropes.
– Not in most plant cells.
http://staff.jccc.net/PDECELL/celldivision/images/metaphase.gif
http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNArep/images/early_late_prophase1_pc.jpg
Prophase
• Chromatin condenses into chromosomes.
– Chromosomes have been copied by now and look
like little X’s.
• Nuclear membrane dissolves.
• Spindle (the “ropes”) forms.
http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/prophase.gif
Prometaphase
• Prometaphase is an intermediate step
between Prophase and Metaphase (obvious).
• YOU DO NOT NEED TO KNOW IT FOR MY
CLASS, but in case you come across it
elsewhere:
– Starts when the nucleus breaks down and spindle
fibers are forming.
– Ends when the chromosomes are being moved
into the center of the cell.
http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNArep/images/metaphase1_ac.jpg
Metaphase
• Chromosomes line up in the middle of the cell.
– Sometimes called the equator.
• Spindle fibers attach (the ropes “hook on”) to
the chromosomes at a site called the
kinetochore (basically the centromere).
http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/metaphase.gif
http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNArep/images/early_anaphase1_pc.jpg
Anaphase
• Centromeres divide.
– Sister chromatids pulled apart.
– Chromatids move toward the poles.
http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/anaphase.gif
http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNArep/images/telophase_ac.jpg
Telophase
•
•
•
•
Nuclear envelope re-forms.
For just a little while, there are two nuclei.
Chromosomes expand into chromatin.
Cytokinesis begins.
http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/telophase.gif
http://www.bio.miami.edu/~cmallery/150/mitosis/sf8x9a.jpg
Cytokinesis in Animal Cells
• The cell divides.
• Proteins pinch the membrane together
between nuclei – forms a cleavage furrow.
• Cell walls are a little different (next slide).
http://img.sparknotes.com/figures/D/d756b5b73abe2974f3521a828791899f/cytokinesis.gif
http://wpcontent.answers.com/wikipedia/commons/thumb/5/5b/Phragmoplast.png/300px-Phragmoplast.png
Cytokinesis in Plant Cells
• Cell plate forms from vesicles (sent from
Golgi).
– Cell wall is inside the vesicle membrane.
• Cell wall forms on top of the cell plate.
http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNArep/images/telophase2_pc.jpg
Mitosis Summary
• This really cool company called Hybrid Medical
Animations put together an awesome CGI look
at mitosis in a cell.
• http://www.hybridmedicalanimation.com/wo
rk/animation/the-stages-of-mitosis/
• While watching, write down ALL the cell
organelles or structures you see.
– I’ll be fishbowling the answers as we do some
ListBuilding…
Summary of Mitosis
Start with one diploid cell
that has 46 chromosomes.
46
Mitosis
46
End with two cells called?
They each have how many
Twochromosomes?
diploid daughter
cells each with 46
chromosomes
46
Mitosis
• What it actually really looks like (see the
spindles?):
http://www.geekosystem.com/wp-content/uploads/2010/07/donut-mitosis.jpeg
Mitosis Fun Facts
• 300,000,000 cells die and are replaced every
minute – roughly equal to the population of
the United States.
• 50,000,000 cells are born in the time it takes
me to read this.
• Nerve cells do not divide but are replaced
from glial cells through neurogenesis.
Mitosis Rap
• Yep, not kidding…we’re going to listen to a
mitosis rap.
– I didn’t do it…could you have guessed?
Mitosis Rap Lyrics
“I” is for Interphase is step 1
the step before mitosis has
begun.
“P” is for Prophase is step 2
the chromosome double dog
that’s what they do.
“T” is for Telophase is step 5,
right
two daughter cells are made in
both of our life…a’ight.
Mitosis tells all my cells to
divide.
“M” is for Metaphase is step 3
Each cells put chromosomes to
the chromosomes line up as you opposite sides.
can see.
It makes daughter cells that
are two of a kind, two of a
“A” is for Anaphase is step 4
kind.
as chromosomes move away
from the core.
Other Mitosis Stuff
• Mitosis App
– https://itunes.apple.com/us/app/mitosis/id34818
4626?mt=8
• Mitosis – Phase Contrast Microscope
Cell Division Gizmo
• Now, we’re going to put our knowledge to the
test with a gizmo from ExploreLearning.
– Called Cell Division Gizmo.
– Directions are on the accompanying Quia quiz
called Cell Division Gizmo.
– [Log-in Instructions]
• When you are done, attempt the Quia quiz
called Labeling Mitosis.
– This one’s important!
Exit Ticket
• Exit Ticket:
– Cells spend most of their time in which overall
stage of the cell cycle?
– Which stages does the cell enter when it is not in
this phase?
– What are the steps, in order, of mitosis?