Area vs. Volume:
Surface Area= width x height x depth x # of sides
Volume= width x height x depth
The volume increases faster than the surface area does causing the ratio of
A/V to decrease
Question: Why do cells need to divide?
Answer: Because if they don’t divide, the cell will continue to get bigger and
bigger and the cell will have more demand that it can’t serve- like there will
not be enough DNA to go through the whole cell because there is a finite
amount of DNA. The bigger the cell gets, the smaller the ratio of surface area
to volume becomes.
Binary Fission in Prokaryotic Organisms:
Bacteria reproduce by an asexual process called binary fission (Binary= two.
Fission=break apart). First, the DNA replicates and the cell elongates. In the
middle of the elongated cell, a septum forms and this develops in to a cell wall
that divides two separate cells.
We get vitamin K from e-coli which is important for blood clotting
The cell wall of an e-coli is made of peptidoglycan
In a prokaryotic cell, there is no nucleus, but there is a chromosome (bacterial
Binary Fission is a 6 step process:
1. A mesosome will form and attach to the chromosome
2. A second mesosome will form, and each mesosome will attach to one of
the strands of the double stranded chromosome
3. The strands begin to separate
4. This is the theta replication stage- because a shape like a theta (script o)
begins to form
5. This stage depicts the original strands with their newly formed strands
6. Final step of the division- 2 separate strands of DNA that are identical to
each other, as well as their parent cell
Ex= E. Coli- the relationship between
e coli and humans in mutualistic.
Each circle is made out of two strands
of DNA and each of those strands are
complementary to each other but in
all, the 2 daughter cells are identical
to each other and to the parent cell.
The Cell Cycle in Eukaryotic Organisms:
A chromosome is made out of two identical sister
chromatids which are connected at a region called
the centromere. Each chromatid is made out of
chromatin which is DNA and histone proteins that
help to compact the DNA. Kinetochore fibers are a
type of spindle fiber made of microtubules. This
allows the chromosomes to slide up and down the spindle fibers during
mitosis. Kinetochore is the region that connects the chromosomes to the
The cell cycle consists of:
Each of these has sub-categories:
1) G1 phase- G=gap.
This phase is the first part of interphase and occurs right after mitosis.
At this point the cell is “a baby cell” so a lot of catabolism and
anabolism take place.
This phase is the only point of the cell’s life at which the cell has the
correct amount of DNA (because later it replicates)
At the end of this phase, there is a restriction point. The restriction
point decides if the cell can pass through and get to the division phase-
this is why some cells divide a lot (ex-stem cells or skin cells) and some
almost never divide (ex- neurons). If cells can’t pass the R point they
are arrested and just stay there.
2) S phase-S=synthesis
This phase consists of DNA replication. DNA is synthesized- or
replicated so that the cell can divide later on during mitosis.
3) G2 phase- G=Gap
The replicated chromosomes loosely coil up.
During this phase, chemicals demolish the cytoskeleton so that the
microtubules can help rebuild the spindle fibers (during prophase) to
enable it to go through the rest of the cell cycle- mitosis…
The nucleolus begins to disintegrate and disappears.
Separate chromosomes are not clearly visible but the chromatin has become
thicker and shorter
In animal cells, the centrioles begin to move apart from each other towards
Later in prophase, microtubules begin to form spindle fibers between the poles
Later in prophase, aster rays appear
apparatus is fully formed
Late in metaphase, chromosomes line up at the equatorial plain of the cell- the
polar fibers also meet and overlap at this point.
Separate spindle fibers become attached to the centromeres of each
Aster fibers help bind the whole spindle
There are two types of spindles:
o Kinetochore fibers-connect to the centromere of a chromosome with the
help of kinetochore. These kinetochore fibers still allow the chromosomes to
move up and down during metaphase and anaphase.
o Polar fibers- polar fibers go from the centrioles at the end of the two poles to
the center and do not connect to the kinetochores.
Chromatids separate at the beginning of this stage
A chromatid from each pair is attracted to each pole of the cell
There is one set of single-stranded chromosomes at each end of the cell during
The reappearance of the nucleus can be noticed
Nuclear membrane reforms around each set of chromosomes
The nuclear membrane forms from the ER
The chromosomes lose their
distinct form and once again
appear as a mass of chromatin
(chromosomes lengthen and
Spindle fibers disappear
Aster rays disappear
Cell membrane begins to
pinch together at the cells
Cell plate begins to appear
midway across the cell
The cell plate forms from
membranes of Golgi Bodies or
Cell membrane pinches
completely together so that the
single cell is separated into
two daughter cells.
Cell plate is completed to form daughter cells
History and Experiments on DNA
Griffith and Transformation Experiment:
Frederick Griffith-British scientist- 1928- studied bacteria- specifically
bacteria causing pneumonia.
Now, to get rid of this, we have vaccines (Fleming invented penicillin
later on)- take the bacteria or virus (antigen=foreign substance),
weaken it, and inject it into the body. This causes the immune system
to manufacture many antibodies that stay in the body and in the event
of getting that same disease, the body will recognize it and be able to
fight it off.
Bacteria cells that cause pneumonia are called pneumococci and
appear in two different types of cells:
1. Cells with capsules- they look
smooth because the capsule
surrounding the cell
membrane is made of
carbohydrates which make it
look shiny. These cells are
2. Cells without capsules- looked
rough under the microscope
because it doesn’t have a
capsule. These cells are non-
Membrane Wall Capsule Membrane Wall
virulent- not deadly
Griffith wanted to figure out the “transforming factor”- what made cells
virulent or non-virulent-
Griffith’s Experiment- Transforming Factor
First, injected live, encapsulated, virulent bacteria in mice and they
died. Next, injected live, non-encapsulated, non-virulent, bacteria in
mice and they lived. Then he heats virulent bacteria and injects the
Heat-killed (not replicating anymore) virulent bacteria in mice and they
live. Then, he mixes the heat-killed virulent bacteria and the live non-
virulent bacteria and injects it in the mice and they die. This was
puzzling- it seems like they should have lived because when both were
injected alone, the mice survived… He decided to do an autopsy on the
dead mice and in the blood sample he saw live, encapsulated, virulent,
Question: how did this happen?
Answer: since DNA is very stable, the DNA from the “heat-killed
virulent cells” survived and got into the live- non- virulent cells. Now
the DNA from the virulent cells could provide the genetic information to
make capsules and become live virulent cells. Biologists inferred from
this experiment that generic info could be transferred from one
bacterium to another- the next step was for Avery to try and figure out
which molecule played the important role in the transformation.
Avery and DNA Experiment:
Oswald Avery- Canadian biologist- 1940’s-tried to figure out which
molecule in the heat killed bacteria was most important to the
He tried destroying many things like lipids, proteins, carbohydrates
using proper enzymes in the virulent pneumococci cell free extract but
the transformation still happened (they died) meaning they did not
cause the transformation to happen (bc when they were destroyed-it
still happened and cell still died).
However when he destroyed the DNA using the enzyme nucleases,
transformation did not happen (and the cell lived), meaning that DNA
in the nucleic acid, stores and transmits the genetic info from one
generation to the next. Because the DNA was destroyed there was no
information on how to create a capsule which is what made the cells
Hershey and Chase Experiment:
Alfred Hershey and Martha
Chase- American scientists-
1950s- studied viruses- non-
living particles- specifically
Viruses- need a host-parasitic,
Question: What makes a living
Answer: Life functions:
o Cell division
Used phage called bacteriophage
to try to show that DNA in the
generic material. The phage was made up of a head, a neck, a tail, base
plate, and tail fiber- the head/capsid made of protein and protects the
core which is made out of nucleic acid (double stranded DNA), tail-
hallow tube that shoots the nucleic acid to infect the bacteria. Tail
fibers- the part that connects to the bacteria.
First, phage were produced containing regular protein in the head but
32P radioactive labeled deoxyribonucleotides so when the phage
infected the bacteria the 32P labeled radioactive DNA entered the cell
and could be found in the phage that were later produced in the
infected bacteria. This shows that it was the DNA, not the protein, that
carries the genetic info for a new generation of phage.
Second, phage were produced containing 35S radioactively amino acids
(the head). This resulted in a phage population with 35S labeled
proteins but there were no radioactive label in the DNA that was
injected into the bacteria. When the phage attached to the bacteria and
injected their DNA but the radioactivity remained on the outside protein
coat and the DNA was not radioactive so when new phage reproduced
in the bacteria they were not radioactive. Shows that while DNA did
enter the cell and cause the bacteria to become radioactive, the
radioactive protein did not enter the cell and did not cause the bacteria
to become radioactive.
Process= bacteriophage attaches to bacteria and injects the DNA into it.
Next, during agitation, the cell got put in a blender to make the
virus/bacteriophage break apart from the bacteria. Next, during
separation/centrifugation, it was spun to get the bacteria cells to go to
the bottom and the empty shells to go to the top- thereby separating
Structure/Function of DNA:
Watson and Crick: they read all day long about DNA and decided to find the
relationship between DNA structure and DNA function. (DNA function-needs
to carry a huge amount of information. DNA structure- needs to be a big
molecule to hold that information but if it was too big it would not be
efficient so there must be something that makes it coil up or contract.
Molecule most be really stable so it doesn’t constantly mutate and not
be able to pass on info
However, there must be something that allows a glitch/mutation once
in a while.
Must be something in structure to help it make copies and replicate
E. Chargaff: he isolated the DNA of many different organisms and noted that
although there were different numbers of each in each organism- the
percentage of A was equal to that of T and G was equal to that of C.
Linus Pauling: first to show that many proteins coil in their secondary
structure- Hemoglobin is folding and coiling in a certain way because it is so
big- alpha helix.
R. Franklin + M. Wilkins: X-ray diffraction-used X ray prints and got an
image of a thick circle with a bold X-like circle in the middle- the X was the
helix- the nitrogenous base pairs. And the dark around it was the
phosphate groups and sugar.
Watson and Crick: they saw this picture and figured out the relationship
between the structure and function.
1. Purine: 2 rings- Adenine and Guanine
2. Purimidine: 1 ring- Thymine and Cytosine (and Uracil)
o double stranded
o the bases are complementary meaning G=C base pair and
T=A base pair – base pairing results in 2 complementary strands.
o because the bases are complementary, the strands are equal in
length- 2 nanometers
o Although these strands are complementary, they are not parallel-
even anti-parallel because on the top of one side the backbone- the
5th carbon of the 5 carbon sugar is connected to oxygen of the
phosphate group (“5-prime-end”). On the bottom there is a “3-prime
end” The complementary strand of this DNA goes in the opposite
direction (3 on top and 5 on bottom)
o A and T both form double hydrogen bonds so that’s why they
always bond together and G and C both form triple hydrogen
o Covalent bonds, which are stronger, are used to bond phosphate
group to sugar (backbone/uprights)
DNA Synthesis/DNA replication
Replication- making an exact copy
When DNA replication occurs, the middle of the helix will open up, with
the help of the enzyme helicase
The enzyme, DNA polymerase, will start looking at the original strands
that have separated, and it matches them with their base pair
Original strands- template
Question: How many times in the life of a cell will DNA replication occur?
Answer: Once, during the S phase of interphase
This is known as semi-conservative replication: the result of replication
are two identical molecules that are double stranded- one is new and one
is old. This is when the new strand bonds to the old, so the old strands is
still being used.
The most important enzyme in DNA synthesis is DNA polymerase
DNA polymerase breaks apart the base pairs because the hydrogen
bonds are weak
The nucleotides that come when the base pairs are broken apart, come
from the cytoplasm in prokaryotic cells, and the nucleus in eukaryotic
The nucleotides have 3 phosphate groups, and they break 2 off to create
energy so the molecule can be stable- if it goes through a reaction that is
so exergonic, the reaction will not be able to be reversed.
The energy that is produced from breaking the two bonds is used to
connect the nucleotides which are what makes them so stable (it will now
need a lot of energy to undo those covalent bonds).
This process is universal- happens in all living organisms and happens
Human DNA consists of nearly 3 billion base pairs
Base pairs can be written as shorthand- BP
The width of DNA is 2 nanometers whereas the pores in the nuclear
membrane are less than 2 nanometers… so how does the genetic info get
out? – it is made into copies of RNA.
DNA replication Fork… sheet.
Hershey and Chase:
f::Hershey and Chase Experiment