DNA carries the “Code” of
Information that determines the
Structure and Function of the cell and
organism.
Absolutely must be protected and
controlled to maintain the cell.
Yes – it really does form a “double helix” as
shown in this TEM.
The DNA of the Eukaryotic Cell is located in the
Nucleus.
This Protected, Separate, and Special environment
protects and supports the function of DNA. The Nucleus
has Pores that allow for entry and exit of various
materials such as Nucleotides and RNA.
DNA Workshop!
The Cell Cycle
The repeated
sequence of
growth and
division of a
cell.
Some cells go
through the cell
cycle continuously,
constantly dividing
and replacing
themselves = Skin,
Blood, Intestinal.
These are called
Mitotic Cells.
Grow to replace
and repair! Know
G1, S, G2.
Most Cells DO NOT constantly Divide! These Cells leave
the Cell Cycle and live in G0.
Cells that Divide often are generally special and are often
called “Stem” Cells. They are found in certain places
throughout the body keeping the body repaired. They have
no real JOB other than to replace/repair damage.
G0 – Many cells of the body DO NOT DIVIDE!
Cell Division requires so much energy and activity that Stem Cells do
little else. This means that dividing cells cannot do any other specialized
jobs. They Grow and are usually Round! So, most cells are not “in” the
Cell Cycle – they are performing their role for the organism.
G0 examples: Neurons and Muscle cells typically do not Divide.
They are too specialized to change as adult cells. Cannot afford
to change/lose them! Non-Mitotic!
Why do Cells Divide?! Usually Activated for Healing!
Often related to growth and Size. Large Cells face problems from
Metabolic Need vs. Metabolic Supply!
As Cells enlarge, Surface
Area and Volume both
increase!
But, Volume increases
Faster!
Volume = NEED!
Surface Area = SUPPLY!
6:1
ratio =
lots of
surface
area.
3:1 ratio =
less surface
area as the
cell grows.
More
NEED!
3:2 ratio = the
larger cell is
running out of
Supply as the
Needs continue to
increase.
So, once cells reach a
certain size, they HAVE
to Divide or
Starve/Suffocate!
Mitosis maintains
Homeostasis!!
Growth allows Cells to do certain things, but poses a
problem as the Cell Increase in SIZE!
Growth
Growth
S.A. =
6 u2
S.A. =
10 u2
S.A. =
14 u2
Volume
= 1 u3
Volume
= 2 u3
Volume
= 3 u3
Ratio of
Supply
to Need.
Ratio of
Supply
to Need.
Ratio of
Supply
to Need.
6/1
5/1
GOOD!
OK?!
Before the Cell
gets Too Large,
It will be forced
to Divide!!
Back to GOOD!
4.7/1
Not
Good?!
What happens as the cells
increase in number?
Normal cells will grow to
fill an area and then stop =
Replacement!
Fast
Growth
Slows and
Stops!
Got
Room!
When
Crowded!
Liver Cells
Grow Until
they almost
Touch each
other, but
then Stop.
Contact
Inhibition!
Cancer Cells do not stop growing because their cannot control the CELL
CYCLE any longer. They press against each other and keep dividing!
But the Cell Cycle can go wrong if the controlling genes are
damaged = Mutation!
Specialized Useful
Cells That WORK!
Useless Cells!
That Just GROW!
Useless Cells!
Useless Cells!
That Just GROW!
That Just GROW!
Progressive Cancer of Glandular Tissue.
Note the difference in Cell Structure and the emergence of the
cancer cells from the mass. The Cancer Cells keep spreading,
but never can specialize since they ONLY DIVIDE!
Tumors and
spreading
cancer cells
are not killer
cells, but they
take up space
and do
nothing. So,
they interfere
with the
normal
functioning of
the body.
The
“working”
cells get
squeezed out!
But the CellThis
Cycle
can go
Tumor developed
Wrong!
before birth! Notice
the aggressive
Cells that have
beenofchanged
recruitment
blood
vessels
to nurture
due to genetic
damage
so the
they
growing cells.
cannot control the Cell Cycle
Its growth is causing
become Cancerous.
These ofcells
shape abnormalities
face,the
but since
are “locked”the
into
Cellthe
Cycle
infant’s cells are able
and cannot stopto dividing.
Thus,
grow, it was
they grow in atreatable
perpetual
and
and the
damage reparable.
rapid state. Tumors
will “use”
the body and eventually spread
to endanger the body’s
Homeostasis.
These cells on the ankle are
growing and do not look right!
They have not specialized as skin
cells because they cannot stop
dividing.
8 lb intestinal tumor removed from a 70 lb dog.
12 lb glandular tumor. She did not have health
insurance that would cover the surgery until
NOW!
Cancer Cells are “stuck” in the Cell
Cycle!
Since Cell Division is VERY EXPENSIVE – have
to copy all of the organelles, DNA, move the
materials around, reorganize the Daughter Cells
(WOW!) – Cancer Cells have amazing needs.
They are so active that they are plugged into the
circulation and steal materials from the body all
the time.
One of the symptoms of cancer is Fatigue!
Chemotherapy quite literally “poisons” the body.
That is why Chemotherapy causes nausea and
other negative effects. But Cancer Cells absorb
the poisonous substances fast and the most – and
CANNOT STOP – so they are supposed to
be killed first.
Have to get them ALL!
Most Cells that are dividing do not have the time to
specialize before they are dividing again. In constantly
growing tissues, Stem Cells form the mature cells that
actually do the job! The specialized Mature Cells are not
Dividing or Growing (= G0)!
Interphase!
The Between “Phase” of the Growing Cell.
Most of the Cell Cycle, even in a rapidly dividing cell, is
spent in Interphase. This is a phase of preparation and
manufacture with discrete stages. The Dividing Cells have
to have all of the materials they need to survive!
G1 stage – Growth 1
S stage – Synthesis
G2 stage – Growth 2
Cell grows. Longest
phase because of the
cell activity “making”
cell materials.
Cell copies its DNA to
prepare for division.
Now two copies of
every chromosome.
Short phase during
which the cell organizes
the cytoplasm to
prepare for division.
Copying Cytoplasm!
Copy DNA!
ALL
TO
DO
M Phase
= Mitosis!
Cells of your body have
to share space and
function to keep the body
alive. So, control of the
Cycle is critically
important.
The ability to change the
cycle could help us
control other cells and
deal with various
diseases or disorders.
Need to grow new cells =
Possible! Need to Kill
Cells = Already being
Done!
Nobel Prize in Medicine
in 2001 dealt with Cell
Cycle controls!
Binary Fission in
Prokaryotes
Bacteria are very simple cells
compared to Eukaryotic cells.
They have a single chromosome that,
when duplicated, are pulled into the
daughter cells because they are
attached to the cell membrane. The
growing cells then divide when a new
membrane separates them.
Really simple process because there is NO nucleus
interfering with separation of the copies of the DNA
chromosome.
Mitosis = Asexual Cell Division
in Eukaryotes
Mitosis is a process of Cell Division in which the original cell is
duplicated to form identical Daughter Cells.
The Chromosomes of Eukaryotic Cells have to be supercoiled,
individually organized, grabbed, and then pulled apart so the Daughter
Cells get complete complements of DNA. This is all performed by the
Cytoskeleton.
Big Problem! There is about 1 meter of DNA in every Human cell. Over
10 billion miles of DNA in a human body!
It has to fit into the nucleus and be useful.
The Egg is 0.0006m in diameter, but holds
1.0m of DNA
The Sperm is 0.000003m in diameter, and
still holds 1.0m of DNA
This is done by carefully coiling it up like string or yarn.
This TEM shows a nucleus of
an active cell.
The Lighter Areas are
Chromatin – active DNA that is
being used to make RNA.
The Darker Areas are
partially coiled-up DNA that is
usually not active. The DNA
can coil and uncoil as it is
needed in some cells, but this
allows for the cell to control
what portions of the DNA are
functional.
The Nucleolus is dark
because of what?
When fully Coiled-up, the
DNA becomes visible structures
called Chromosomes. They are
only present during Cell
Division!
Mitosis can only occur after the chromosomes have supercoiled and
become visible.
Chromosome actually means – “chromo” = colored, “some” = body.
How does the DNA coil-up into these compact and easily separated
structures?
Chromosomes are completely shut down DNA – But packaged into a
discrete form that can be moved!
A Supercoiled Chromosome. This supercoiling only occurs during cell
division when the DNA has to be moved around within the cell. This
usually happens when the DNA has been duplicated. So, there are two
copies of each molecule here. Those copies should be identical and are
called Sister Chromatids.
The Chromatids are held together by proteins at the
Centromere.
The Mitotic Spindle
The Cytoskeleton controls the movement of the Chromosomes. It does
so by connecting with the individual chromosomes and then pulling them
toward the opposing ends of the cell. The Centromeres possess proteins
that bind with the cytoskeleton to be moved around.
Like 4
1 – Bare DNA that would be
available to provide
information.
2 – DNA coiled up on proteins
called Histones.
Like 2
Like
1,3,5
3 – “Coiled” DNA where the
“beads” of DNA + Histones
align together. Inactive!
4, 5 – Supercoiled DNA.
Wrapped-up and Inaccessible
for use.
“Beads-on-a-String” arrangement
of Chromatin. DNA is always
associated with Histones in
Eukaryotic cells.
Chromatin is inside
the Nucleus in
various states on
“on” (active = very
loose and openable!)
and “off” (inactive =
coiled and closed!).
NOW – Visible!
NOW –
Separable!
But, all of the DNA is
present!
NOW – OFF!
And as Chromatin –
Not “Visible”!
CHROMOSOMES!
Usually Mingled
Pieces! Not
Separable!!
BUT, If the Cell is going to
Divide, it will COPY the DNA!
And then COIL IT UP!!! The
Cell is now “OFF”!!
Chromatin is Angel Hair Pasta – Can’t be Pulled Apart!
Chromosomes are Raviolis – Countable and Separable!!
Prokaryotes (Bacteria) have
only one chromosome. There is
only one copy (= haploid) and it is
attached to the cell membrane.
There might be small satellite
pieces of DNA as well called
plasmids.
Easy to Manage!
Eukaryotes have much more
DNA in multiple Chromosomes.
There are typically two copies of
each piece (= diploid).
Difficult to Manage!
This is a Human Karyotype. It shows all of the chromosomes present in a
sample cell from the individual. Each chromosome has two copies
(=diploid), one from each parent that have been duplicated. Humans
have 23 different chromosomes, but since there are copies of each from
each parent, almost every human cell has 46 chromosomes.
By the time Mitosis occurs, the DNA has
already been copied (S Phase!).
So, the chromosomes always have two
identical Sister Chromatids.
The “X” is actually two “V”’s that are
connected. During Mitosis, they will be pulled
apart. Chromosomes are coiled up TO BE
SEPARATED!!
Interphase!
Cell could be in G1, S, or G2 –
sometimes you can tell – but the cell is
active and doing something!
How do you know?
Prophase
“Pro” = First or Before.
1. The loose Chromatin of Interphase coils
into solid and obvious Chromosomes. These
Chromosomes are typically scattered in the
nucleus, but visible!
2. The Centrioles migrate to the Poles and
begin to form the Mitotic Spindle.
Metaphase
“Meta” = Middle
The Mitotic Spindle Fibers connect with the
Centromeres of every Chromosome and while
pulling on them they align at the Equator of
the Cell.
Anaphase
“Ana” = To cut and pull Apart
The Chromosomes are separated and
pulled to the Poles of the Cell. The
chromosomes form V-shaped wedges
because they are being pulled through the
thick cytoplasm.
Telophase
“Telo” = Tear
The Separated Chromosomes are re-packaged into new nuclei
that are contained in their new cells. The Spindle disappears.
Cytokinesis
“Cyto” = Cell, “Kinesis” = Motion
The Cells are separated into the Daughter Cells.
Plant Cells – separate through formation of a “cell
plate” that extends the Cell Wall to bifurcate the
original cell.
Animal Cells – are “pinched” apart through action of
the Cytoskeleton that pull through the original cell with
a “cleavage furrow”.
And back to Interphase!
“Inter” = Between
Nucleus reforms
Chromosomes fully unwind to become active
chromatin and the genes activate to carry out cell
function.
Mitotic Spindle disappears as the Cytoskeleton
reassembles to support the appropriate Cell’s
Shape.
What Phase of Mitosis is shown
in this Photograph?
What Phase of Mitosis has
been photographed here?
The intense Yellow
structures at the Poles
control the movement of
the blue structures. What
are they?
What Phase of Mitosis is
shown in this Photograph?
The central dividing line
shows the division of the
two daughter cells. What
is this process of
cytoplasm division called?
What is shown in this picture? What is this called?
What is the Sex of the Individual that possesses this DNA?
ONWARD (and in
Conclusion)
Mitosis
The Process of
Asexual Cell Division.
This process lines up
ALL of the
Chromosomes
individually and pulls
apart the Sister
Chromatids to make
identical Daughter
Cells.
Growth, Development
and Healing,
Replacement,
Cloning, Consistent.
What a great Picture!
Mitosis is all about separation of the same materials. Once
those blue Sister Chromatids have been pulled apart, he
resulting Daughter Cells should be Identical.
Mitosis supports replacement and maintenance. The fish
grows because it is adding cells that are genetically the
same. The Daughter Cells are consistent!
Meiosis is
different.
Sexual reproduction
is all about
making organisms
that are different
from the original
parents through
sharing their
DNA.
Meiosis makes cells
that transport ½
of the parents
DNA so they can
fuse into a new
organism.
Terms you have to know and understand:
This is a fertilized egg called a Zygote.
It is Diploid because it has received Two
(2n) sets of chromosomes from the
parents.
The Sex Cells that deliver the
parental DNA are the gametes.
They are haploid, meaning they
carry One (n) copy of each
chromosome found in the species.
The only way to share information
in the offspring is to deliver half of
the information – but all of the
chromosomes are there!
Terms you have to know and understand:
Homologous Chromosomes are the
pairs of chromosomes present in a
diploid organism. They are the
same size, structure, and carry the
same genes, but not always the
exact same info! Having them be
present and working together is
essential to life.
You need Both!
This is why chromosomes are
always paired in normal cells.
Humans have 23 different
chromosomes, but they are
usually found as pairs –
making 46 total.
Keep an eye on the pairs
during Meiosis!
Meiosis – Process of making Sex Cells
The entire purpose of Meiosis is to
make Gametes.
Unlike Mitosis, these cells carry only
one of each chromosome, and they
are all variable!
Two Cell Divisions make four cells
from the original Germ Cell.
They are haploid and have
different sets of chromosomes –
Why?
Two reasons! Can you see them?
Mitosis ensures that all cells
get the same stuff –
Meiosis separates them differently!
Daughter Cells are Identical!
2: Crossing-Over
1: Independent Assortment.
The homologous chromosomes are
pulled apart first – not the identical
sister chromatids.
And not until after they swap pieces
of DNA between the different
homologous chromosomes.
Gametes are Different!
Swapping of pieces of DNA is called “Crossing-Over” and happens
during Prophase. They are actually “stuck” to each other as the Tetrads.
BUT – ONLY HOMOLOGOUS CHROMOSOMES
There is a Problem with Crossing-Over!
If they are directly connected - what might
happen when they are pulled apart?
NONDISJUNCTION
Be Opposite!
Together!
0 or 2?!
Tetrads
BAD!!
Not!
The chromosomes should
pull apart evenly during
Anaphase, but sometimes do
not.
Now – deletion or addition of
extra chromosomes or pieces
of chromosomes! BAD!!
Should be Only ONE Copy!
AMNIOCENTESIS!!
So, how do you get a sample for Karyotyping from a fetus?
Extract a sample from the liquid surrounding the fetus. A sonogram is
used to keep the needle from hitting the fetus or placenta.
Have to “see” the chromosomes! This only happens during cell
division. The Cells are treated with a drug to force Mitosis to get the
chromosomes to form. They can then be organized.
What should be Present?!
What should be present?
Can you identify the problems with the
Karyotypes shown here?
Trisomy X
Turner’s Syndrome
All of the Chromosomes CAN do this,
but most changes are Lethal!
Chromosomal Mutations are Random,
so anything could happen.
The Sex Chromosomes are less
important than the Autosomes and
survival of these changes is more
likely.
Klinefleter’s Syndrome
Deletion – Cri du chat
Other errors during Crossing –
Over can impair an organism.
Most are Lethal, but some are
survivable.
Duplication – Fragile X
Any chromosome and any
error can occur.
Down’s syndrome is the most
common chromosomal defect
because it is survivable
Making the cells is only half of the process!
Sperm
are small
and
compact
– to swim
and find
the Egg.
So, all
four cells
are
turned
into
gametes!
Sperm and Eggs are highly specialized cells that
have to develop further.
Males
make
many all
of the
time!
Now –
Eggs are
HUGE
and
precious
cells –
ONLY
ONE is
made
from
each
Meiotic
division!
The rest
are small
and
discarded
!
Eggs have to hold all of the materials to start
development and are a major investment for the female.
These are Sperm Cells – what is the official name for highly
specialized Sex Cells such as these?
How many copies of each chromosome do they carry?
What is that Condition called?