Download Cell division and Mitosis

Cell Division and Mitosis
Work to begin class with
• Why do humans always have to cut our hair,
fingernails, and even the lawn? (and your
answer cannot be because it gets long). There
is a scientific answer
Cellular differentiation
• Cell tissues organs organ systems
• As cells grow and divide, many of them may form
tissues inside the body
– Muscle Tissue
• If many tissues group together, they form organs
– Ex: Liver
• Organ systems are the same as body systems it
is when multiple organs work together to achieve
a common goal
– Ex: digestive system
Cell Growth
• Living organisms obviously grow in size as they
age, but how?
• When a cell grows, do the individual cells get
larger therefore increasing the size of the
organism?
• Do the number of cells increase therefore
increasing the size of the organism?
• On average, the size of a cell in a baby, and the
size of a cell in an adult are about the same
• Instead the number of cells dictate size of the
organism
Why do cells divide instead of just get
larger?
• The larger a cell gets, the more demand it puts
on DNA to control the cell (DNA is the same
regardless of size)
• Large cells are not very efficient
• Transport is very difficult
• Cell division makes it easier to dispose of bad
cells
• If you had fewer larger cells, you would lose
large portions of information when a cell dies
Exchanging materials
• The larger a cell gets, it is harder to remove unwanted
objects from the cell, and it is harder to obtain the
things the cell needs from its outside environment
• The surface area of the cell dictates the rate at which
objects can be transported into and out of the cell
• This is better known as the surface area to volume ratio
• It is optimal to have a high surface area to volume ratio
• Analogy a small town with limited supplies is good as
long as there are not a lot of people
– As the town gets larger, the amount of supplies per person
decreases, causing problems
– It is in the best interest to keep the town small, everyone
will be happier
Cell division and Mitosis
 If you want to make two batches of cookies
instead of just one, what do you have to do to
the recipe?
Double it
 For a cell to be able to split in two, what does
it need to do?
 Double the “ingredients”
Organelles, DNA, etc.
The cell cycle
 Two main stages
1. Interphase
G1 (Gap 1) cell goes through normal functions (growth)
Checkpoint-cell must be big enough, mature enough, and have
undamaged DNA
Preparation stage for cell division
Synthesis (S) cell makes a copy of DNA; nucleus now
contains two sets of DNA
G2 (Gap 2) additional growth-normal functions
Checkpoint
2. Mitosis and cytokinesis
Cell splits into two cells
Vocabulary
 Chromosome one long continuous thread of
DNA that contains many genes
Looks like an “X”
 Chromatin loose combination of DNA, like a
shoe string with knots in it
 Chromatid one half of a duplicated
chromosome
Half of the X
 Centromere junction between two halves
 Telomere tip of DNA or chromosome
 What’s the relationship between a
chromosome and DNA
A chromosome is made up of DNA
DNA twists and folds itself to make a condensed
chromosome
Mitosis and cytokinesis
 In the end, there will be two genetically
identical “daughter” cells
 Interphase G1, S, G2
 Mitosis
Prophase
Metaphase
Anaphase
Telophase
Interphase
• Preparing the cell to
divide
• Growth phase
• DNA duplication
• Cell has two identical
sets of DNA, or
chromatids and is
large enough to
divide
Prophase
 Chromatin condenses
into tightly coiled
chromosomes
 Nuclear membrane
breaks down
 The nucleolus disappears
 Centrioles begin to
migrate to opposite
poles
 Spindle fibers-made up
of microtubules begin to
grow from centrioles and
form whats called the
mitotic spindle
Metaphase
• Spindle fibers
attach to
centromere of
each
chromosome
• Chromosomes
line up on the
“middle”
Anaphase
 Chromosomes split,
resulting in two
sister chromatids
X splits in half
 Spindle fibers begin
to shorten which
pulls the chromatids
away from each
other
Telophase
• A complete set of
identical chromatids is
positioned at each pole
• Nuclear membrane
begins to reform in each
cell
• Chromosomes begin to
uncoil back into
chromatin
• Spindle fibers fall apart
Cytokinesis
• Divides the rest
of the cell into
two pieces
• Actual splitting
process
The cell cycle control system
• Checkpoints critical control point where stop
and go-ahead signals can regulate the cycle
– G1 checkpoint
– G2 checkpoint
– M checkpoint
• External factors
– Cell to cell contact
– Growth factors protein signals from neighboring
cells that stimulate cell division
• Internal factors
– Apoptosis programmed cell death
Cellular differentiation
• Cell tissues organs organ systems
• As cells grow and divide, many of them may form
tissues inside the body
– Muscle Tissue
• If many tissues group together, they form organs
– Ex: Liver
• Organ systems are the same as body systems it
is when multiple organs work together to achieve
a common goal
– Ex: digestive system
Differentiation
• When sperm and egg come together, one cell is
created
• That fertilized egg gives rise to an increased
number of cells through cell division, which must
divide creating identical cells
• As cell division proceeds, cells also undergo
differentiation, becoming specialized in structure
and function
• This happens, because all cells contain the same
DNA, all cells initially have the potential to
become any type of cell
• Once a cell differentiates-becomes specific cell- it
cannot be reversed
Stem cells
• Stem cells unspecialized cells that
continually reproduce themselves and have,
under appropriate conditions, the ability to
differentiate into one or more types of
specialized cells
• Two types:
– Embryonic-embryos at a very early stage
– Adult- various places in body can be stem cells
• Under appropriate laboratory conditions, stem
cells can differentiate into specialized cells
Application-Uncontrolled cell division
• Cancers use the process of cell division to
make bad cells multiply without any control
• Cancers form disorganized groups of cells
called tumors
– Two types:
• Benign cancer cells typically remain clustered
together. This usually means that the tumor is
harmless and can be removed
• Malignant some of the cancer cells can break away,
or metastasize from the tumor. These cells can be
carried in the bloodstream or in lymph nodes and can
form new cancerous tumors in other places
Carcinogens
• Carcinogen substances known to promote
or produce the development of cancer cells
• Smoking, drinking, drugs, too much of a lot of
things can lead to cancer and apoptosis
• Sometimes your body can detect when there
is a problem
• Ex: skin cells
Treatment for cancer
• Radiation therapy the use of radiation to kill
cancer cells and shrink tumors.
– It works by damaging the DNA of cells so they
cannot divide
– Radiation is localized-its use is targeted to a
specific region-because it can hurt regular cells
• Chemotherapy the use of drugs/poisons to
kill actively dividing cells
On your final sheet to turn in
• Write a good test question on something we
covered today.
• Write down something that you are still
struggling with and need some more
explanation on.
• What was the main idea of the lesson today?
(your answer must be a sentence, not just
mitosis)