Frank Raucci
Role of Charge-reversal of Colloids in Electrostatic Interactions of
DNA-Lipid Complexes
DNA-Lipid complexes have demonstrated the ability to effectively carry
DNA within living cells. Solutions of negatively charged DNA and
positively charged lipid molecules can be prepared using various mixing
ratios in the lab. In cells, most lipids are either neutral or
negatively charged, thus repelling DNA molecules. By adding the
DNA-lipid complex prepared in solution, the electrostatic barrier for
interaction between the DNA and the cell membrane is lowered. These
DNA-lipid complexes form colloidal structures, with a total effective
charge dependent upon the mixing ratios of DNA to cationic lipid. If the
total DNA charge exceeds the total lipid charge, then the colloid is
negatively charged. The opposite is true if the total lipid charge is
greater. The specific ratio where the charges are equal is known as the
isoelectric point. This paper will attempt to address the reasons that
neutral DNA-lipid complexes are not commonly formed, as one would
expect, and that instead various liquid crystal-like structures are
observed. The mechanics of these formations, the correlation effects
involved, and the biological utility of the DNA-lipid complexes will
also be examined and discussed in this paper. We will see that simply
assigning a charge to these colloidal complexes does not yield to
observed results. Instead, entropic effects and the structure of the
counterions released in the formation of the complex produce results
that are quite different from the conventional predictions of
electrostatics.
Preston Aleshire
AFM and DNA
The Atomic Force Microscope has been in use since 1986 (AFM). It was
typically used in the past as a probe in order to decipher the atomic
structure of the surface of a substance. The AFM is still used in this
way; however, new applications of the AFM are leaning towards the
"unzipping" of DNA molecules as well as surface imaging of DNA. This is
done by anchoring one side of the DNA molecule by exploiting it's
natural negative Phosphate charge and using the cantilever of the AFM
to "unzip" or pull apart the DNA into individual strands. By measuring
the forces involved in the separation of the base pairs the DNA can be
sequenced. Some of the problems with this technique revolve around the
resolution capabilities of the AFM. This problem is rooted in the size
of the tip (i.e. the atomic width) that is attached to the cantilever.
Yet, current developments are finding new and better materials that
increase the resolution of the AFM. The fore coming paper will deal
mainly with the use of the AFM to unzip DNA. However, there will be
mention of the imaging properties of the AFM.
Dennis Warner
Is Kleiber's Law valid for all ectotherms?
In ectotherms, the scaling law for body mass to metabolic rate, when
based on heat-loss through the surface area of the body, leads to a
scaling factor such that P~M^(2/3). However, Kleiber found
experimentally that the value was 0.738. This lead to the adoption of
Kleiber's Law: P~M^(3/4). The reason the data deviates from the
prediction is unknown. However, one theory suggests the difference
lies in the fractal-like architecture that is found in the vascular
systems of ectotherms. Some, on the other hand, do not agree that
Kleiber's law holds true for all ectotherms, as a 2/3-power law is
predicted mathematically, and findings taken over particular groups of
ectotherms (for instance, all birds or all rodents) do not agree with
the 3/4-power law. Also, ectotherms larger than 10 kg begin to deviate
significantly from the 3/4-power scale. One suggestion is that there
are in fact two parallel 2/3-power lines (one for ectotherms under 10
kg, and one for ectotherms over 10 kg), instead of the single 3/4-power
line on a log plot of metabolic rate versus body mass. Others have
examined individual classes of ectotherms, and have found no reason to
favor a 3/4-power law over a 2/3-power law. In fact, there are a
significant number of deviations from either power that suggest that
the power may vary with body size or shape, and in fact the power may
not have one constant value.
Danny Colvin
Investigating the biological effects of RF radiation exposure
The increasing use of cellular telephones and other wireless
communication systems has prompted scientists to examine the possible
health hazards that could be associated with such devices. Although
much of the recent research has focused on the threat of chromosome
damage and the potential for increased lymphoma through RF
(radio-frequency) radiation exposure, most studies have failed to
establish a "dose-response" relationship. The majority of these
studies ultimately concluded that the energies emitted by cellular
phones via electromagnetic radiation were well below the thermal
agitation energies experienced on the molecular level, and thus,
insufficient to break chemical bonds or damage DNA. However, new
evidence suggests that the real danger of these devices may be
completely unrelated to cancer. Exposing the human head to RF
radiation, for even brief periods of time, can cause rapid thermal
heating of tissues near the brain. This may open the door to a variety
of negative physiological repercussions, including disruption of
neurological activity in the exposed regions, changes in blood pressure
and body temperature, and permanent damage to tissue. Further evidence
suggests that the permeability of the blood brain barrier may also be
highly sensitive to radiation frequencies in this range. Although the
physical phenomena contributing to the problem are contained almost
entirely in Maxwell's electromagnetic relationships, the extent of
their effect on biological tissue is not completely understood. This
paper presents an overview of the physical mechanisms of energy
transfer and absorption in biological tissue, particularly as
demonstrated in animal experiments, along with a discussion of the
relevant thermodynamic properties and physical limits involved in
repetitive tissue heating.
*acknowledgement
J.E. Moulder, L.S. Erdreich, R.S. Malyapa, J. Merritt, W.F, Pickard, Vijayalaxmi, Cell Phones and Cancer: What is the Evidence for a Connection? Radiat. Res. 151, 513-531 (1999)
Peter Wainwright, Thermal effects of radiation from cellular telephones. Phys. Med. Biol. 45, 2363-2372 (2000)
Daniel Zahrly
The Influence of a Biodegradable Polymer's Physical Properties to its
Physical Characteristics and Orthopedic Applications
Polymer Scientists, in conjunction with Medical Doctors, Engineer, and
Physicists, have made amazing advances over the past three decades in the
development and application of synthetic materials into the human body. This
paper will explore the major types of biodegradable polymers currently in use
for the orthopedic applications in which a traditional, permanent implant is
either not desired or feasible. The biosynthetic polymers, currently in the
greatest use are the Poly-Lactides and Poly-Glycolides, and these materials
will be covered in the greatest detail. The chemical synthesis,
microstructure and the mechanisms of biodegradation will also be covered.
The primary focus, however, will center around the relationship between the
individual properties of each of the biodegradable polymers and their
respective physical characteristics and orthopedic applications.
Sam Choe
Vestibular evoked myogenic potentials
Polysynaptic response of the otolith vesitibular nerve origin are
believed to be caused by Vestibular evoked myogenic potentials (VEMP)
that occur in the cervical muscles after intense stimulation by sound
caused by air or bone. I will analyze the data collected from an
experiment titled, "The effect of sternocleidomastoid electrode location
on vestibular evoked myogenic potential" by Sheykholeslami. This will
show if acoustic stimulation of the saccule by bone conduction produces
VEMPs in which response amplitudes are sensivtive to stimulus frequency.
This should be very similar to the effects of air conducted stimuli.
The effect of stimulation repetition rate on bone conducted VEMPs was
conducted at stimulus frequencies of 200 and 400 Hz with five
differenent repetition rates. Bone VEMPs were recorded from 12 normal
hearing subjects in response to bone-conducted 70dB, 10-ms tone bursts
at frequencies of 100, 200, 400, 800, 1600, and 3200Hz. The experiment
showed that bone VEMP amplitudes were the highest at 10Hz and decreased
as the repetition rate increased. Frequencies at 200 and 400 Hz showed
that the bone VEMP response amplitudes were maximal. This contributes
to the perception of loud sounds. The results in the experiments will
then prove that bone VEMP in the sternocleidomastoid muscle has a well
defined frequency sensitive response. This response thus concludes that
it is being mediatated by the saccule.
Nancy Huang
Metachrosis
Metachrosis is the ability of changing skin colors by expansion of special
pigment cells under nerve influence. Chameleons are one of the more famous
living creatures that possess this ability. The change of light,
temperature, and emotions can trigger color change in them. The purposes of
this function are believed to be for protection, communication with others,
and display of emotions. Contrary to popular belief, Chameleons don't
change their color to match their background and they cannot change to every
color of the spectrum. Different species have different base colors and
patterns, which may be their response to their varying environments.
The chameleon skin is made of four different layers that collaborate to
create the various colors that are seen. There is one color cell layer, two
light reflecting layers, and the melanophore layer. Melanophore cells are
the main controls for metachrosis. They contain the pigment granules called
melanin, which is dark-brown in color. The main body of each melanophore
sits like an octopus beneath the light reflecting layers and spreads
tentacle-like arms through the other layers. The melanin is released by the
melanophores in different amounts and changes the size by either swelling or
contracting the cell. When it swells different regions can be covered and
thus altering the color of light being reflected off their skin. More
details are to be discussed.
Ales Necas
Nonlinear behavior of the heart following cardiac arrest
Sudden cardiac arrest is the leading cause of death in the
industrialized world with the majority of such tragedies attributed to
ventricular fibrillation. Ventricular fibrillation is a frenzied and
irregular heart rhythm disturbance that quickly renders the heart
incapable of sustaining life, unless externally applied electric
current through the heart muscle terminates such arrhythmia by
depolarizing the myocardium (the middle layer of the heart wall).
Unfortunately, this electric shock is delivered with a force of 7 J;
such a shock can result in muscle, bone, and connective-tissue damage.
I would like to research a technique using a series of milijoule
control pulses to restore the heart's natural rhythm. Firstly, I will
describe non-linear and chaotic behaviors in its most basic formalism;
chaotic attractor and Poincar section. Next, I will provide discuss
how to deal and study chaotic system. I will talk briefly about a
method that was used ten years ago. However, for this method we must
know the theoretical model and this method is limited to systems that
do not display irreversible parametric changes (often the very changes
causing the chaos). The main part of this paper is to explain a method
developed by Edward Ott, Celso Grebogi and James A. Yorke known as OGY
method. This is a conceptually straightforward technique, which does
not require a detailed model of the chaotic system but only some
information about the Poincar section. I will conclude with the latest
development in the research of administering electric stimuli to the
heart as determined by chaos theory.
Rebecca Boren
Forced unfolding of single biomolecules
Despite the extensive research and studies conducted on molecules such
as DNA and proteins, much is still not known about many of their
properties and characteristics. One of these mysteries concerns the
method of folding that the molecules undergo. Scientists have developed
many procedures that manipulate single molecules using tools such as
magnetic and optical tweezers, glass micro- fibers,
atomic-force-microscopes, and others. In all of these procedures, the
molecule has one end attached to a suitable surface, and the other end
attached to a sensor that measures the force exerted in the stretching
of the molecule. In nature, enzymes perform the stretching,
replication, and repair of DNA. DNA is particularly of interest due to
its ability to be twisted and its stiff nature. By using magnetic
tweezers and other devices to stretch out the DNA strand and unfold it,
new structures can me formed to accommodate the strain of stretching.
Pulling DNA and other proteins, with fluorescent markers attached, to
unfold them can help determine their structures when not in an
equilibrium state. The forced unfolding of these single molecules can
tell us much about their structure and also about the molecular motors
that manipulate them naturally. In addition, an analysis of the force
behind the pulling mechanism as well as the response of the molecule to
the strain can lead to a better understanding of its configuration and
properties, thus improving the theoretical models that represent the
folded structure.
Terence Strick, Jean-Francois Allemand, Vincent Croquette, and David Bensimon.
The Manipulation of Single Biomolecules. Physics Today. October 2001. Volume
54, Number 10.
Ed Grant
Fluorescent Nanocrystals as Biological Probes
Clusters of cadmium selinide that range in size from approximately 2 to
7 nm (roughly 200 to a few thousand atoms) have been shown to have
unique optical properties which may be exploited as tool for molecular
biology. These clusters, known as nanocrystals or quantum dots, when
covered with zinc sulfide monolayers, have a high quantum yield and
large extinction coefficient making then excellent fluorophores. The
emission spectra for the CdSe nanocrystal is size tunable as the
smallest core (1.8 nm) emits in the blue spectrum and larger cores emit
at progressively longer wavelengths, and any wavelength shorter than
the emission will cause fluorescence. Spectral peaks are narrow,
symmetrical, and gaussian thereby allowing for multiple nanocrystal
sizes to be used simultaneously and with a single excitation source
without loss of distinction between them. These aggregates can be
utilized by direct conjugation with biological molecules or may be
incorporated into porous polymer beads. The beads allow for the
observation of both wavelength and intensity by controlling the mix and
number of nanocrystals contained therein. The multiplexed coding
possible may allow for rapid genomic or proteomic assays.
David Elm
Physical constraints on life on Europa
With the exploration of Mars, we find the hope of extraterrestrial life
on mars dwindling. Since a major requirement of life is the presence of
liquid water, we turn to possibilities in and on the moons of Jupiter
and Saturn as the next most likely candidates. In particular we look at
Europa. If there is liquid water under the icy crust of Europa, the
next constraints on life are the availability of energy and raw
materials. Since raw materials (on one level, the various and
biologically scarce elements, including iron that are required in
organic processes and on another, the amino acids) are most likely
tractable without strong assumptions (or taking samples, for that
matter), instead, in this paper, we will address the question of
whether the energy requirements are met, or more specifically we place
upper limits on the "size" of the ecosystem that could be supported.
The mode of energy transfer we will examine is via the robust magnetic
field of Jupiter. We will start with the most general limits based on
the change in magnetic field felt by Europa during an orbit as well as
the attenuation of that field through the 10 kilometers or so of ice.
We will also examine the ionic currents that may be present based on
the measured magnetic field of Europa (under the assumption that the
field is produced by those currents.)
On a side note, we will examine
the question of if the quanta of energy involved is less than the
transition energy from ATP to ADP, then is the energy is essential
unavailable to biological systems for as anything more than heat and so
not important as energy for metabolism. This is a key point on whether
the energy supplied, if it is large, might have thermodynamic
constraints that limit its utility.
Rani Hasan
Tensegrity: The Basis of Mechanotransduction
Living cells exist in dynamic environments in which they are constantly
subjected to physical forces. Speculation that these mechanical stresses play
a role in mediating tissue growth and differentiation originated a century ago,
yet only recently have scientists confirmed that physical stresses influence
cellular physiology. The current understanding of transmission of mechanical
signals into and throughout cells, or mechanotransduction, is based upon a
model of cellular architecture dependent on tensional integrity known as
tensegrity. This structural system is a comprised of a self-stabilized network
in which tensional and compressive forces are distributed and balanced
throughout the entire system. The cytoskeleton is the basis of tensegrity
within cells. Microfilaments and intermediate filaments comprise the tension-
bearing components, while microtubules and bundles of intermediate filaments
have been shown to form the rigid struts bearing compression. Organization of
these components and modifications in the forces distributed through the
cytoskeleton govern cell shape and affect function. Many of the enzymes
involved in metabolism and cell growth are physically immobilized on the
cytoskeleton, which is also linked to the nuclear scaffold and extracellular
matrix. Thus, mechanical forces may be transmitted across the plasma membrane
and throughout the cell instantaneously, which may cause alterations in
cellular shape that regulate cell growth, differentiation, and death; affect
regulation of "solid state" biochemical pathways; and mediate biochemical
responses in conjunction with chemical stimulation.
Justin Brooten
The Physical Principles of Kidney Nephron Function
The Kidneys employ the physical principles of osmosis and ionic
potentials in their regulation of blood solute levels. The glomerulus
is the first component of the kidney nephron and works like a reverse
osmosis filter, using blood pressure to expel small molecules from the
blood, such as water, salt ions and urea, while retaining proteins.
This filtrate passes along the epithelial cells of the proximal and
distal tubules lich regulate their osmolaity, in this very osmotic
environment, by accumulating organic solutes. The reuptake of ions is
regulated along the length of the tubules through a system of potassium
and proton co-transport. This system produce a negative potential
within the cell lining which attracts cations. This potential allows
the cells to reabsorb ionic solutes, such as sodium, while allowing
other non-ionic wastes, such as urea, to be excreted. By regulating the
osmolatity along the remaining length of the tubules, with the
reabsorbed sodium ions, an osmotic gradient forms which favors th