Questions tagged [biophysics]

The use of methods from the physical sciences to aid in the study of biological systems.

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Contradiction between random molecular collisions and regulated cellular processes

A cell is a chemical system, consisting of billions of molecules, ions, and atoms. These chemical species are constantly engaged in chemical reactions. Physics gives the impression that chemical ...
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What is the relationship between muscle energy consumption, the period over which the contraction occurs and the mechanical work performed?

I'm asking this question with some basic knowledge of physics and general fitness. Suppose you are lifting a still object with mass $m$ from height $h_1$ to height $h_2$ with an arbitrary (straight or ...
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Can tissue flow apart instead of being tightly attached?

Every tissue of our human body consists on cells and cells are not like static "LEGO bricks". They are highly dynamic and can actively move around, due to myosin-actin networks inside the ...
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How to understand the biophysics and math behind a 0.2 second delay between the pulse in my arm and my ankle?

I recently had a test with six blood pressure cuffs; 2 each on arms, ankles and big toes. During the test I could feel the pulses in my arms and legs, and noticed a distinct ~0.2 second delay between ...
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What does it mean to quantitatively describe a cell?

To begin this question, I will quote Molecular Biology of the Cell (page 38): ... Biological systems are, ..., full of feedback loops, and the behavior of even the simplest of systems with feedback ...
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Is the principle of "the least energy" a fundamental principle of evolution? How does it stand with the rule "the one who replicate the most"? [closed]

The principle of "least energy" seems to be a fundamental law of the universe (is it?). I probably use the wrong word. I'm just talking about the reason why electrons are filling first the ...
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Types of structures formed by various types of lipid molecules

Since Phosphatidylcholine (PC) and phosphatidylserine (PS) are roughly cylindrical in shape , they tend to form flat bilayers. Phosphatidylethanolamine (PE) on the other hand is conical in shape which ...
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How do physics notions of fluid dynamics relate to pressure gradients in circulation?

I'm having a hard time comprehending why sometimes physiology notions seem to contradict each other and contradict physics teachings. More specifically I don't understand why aortic coarctation causes ...
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Why does UV radiation from the Sun cause skin cancer?

What is the specific mechanism makes non-ionizing UVA and UVB radiation carcinogenic? Can lower energy light, like visible light, be carcinogenic because of this mechanism, or is there some kind of ...
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Examples for oscillatory behaviour in the human body

I'm looking for examples in the human body which show periodicity, more precisely, I'm looking for examples of oscillating reactions that occur in the human body which can be modelled using the ...
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Why do water molecules diffuse along axons direction?

I am studying tractography technique which aims to reconstruct bundles of axons in brain by following the diffusion direction of water. It is very interesting because it is non-invasive. It exploits ...
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Adaptive Optics in Microscopy: what are the fastest processes in specimen causing optical aberrations?

Some companies e.g. the one of Nobel prize winner Stefan Hell (Abberior) are offering Adaptive Optics enhancements for microscopes for allowing deeper focus in locally changing optically refractive ...
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Do electric eels produce current as they just move about, and how/why?

https://www.youtube.com/watch?v=y9wktSQdyaE This video demonstrates how an electric eel can supposedly produce up to 800 watts, and power a Christmas tree, which is very topical (a late Merry ...
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Thermodynamic noise determining gene expression?

I'm wondering if and how thermal noise may randomly determine gene expression? Looking for cellular and 'transcriptional noise' one finds hints to diffusive cellular dynamics which rely on collisions ...
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Has anyone tried using functional near-infrared spectropathy to quantitively measure sodium concentrations in the brain?

Functional near-infrared spectropathy "fNIRS", is a biophysics/medical technique that uses the near-infrared part of the electromagnetic spectrum (around 680nm to 810nm in wavelength) to ...
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The Effects of Large Static Magnetic Fields on the Human Nervous System

How do static magnetic fields impact the nervous system? I imagine with sufficiently intense magnetic fields the Lorentz force is going to change the behavior of nerve impulses, but at what field ...
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What's a cells membrane potential without any leak channels?

Consider the following ion concentrations on either side of a cell membrane (in = inside cell, out = outside cell): $[\text{Na}^+]_{\text{in}} = 10mM$, $[\text{Na}^+]_{\text{out}} = 142mM$, $[\text{K}^...
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Why is a solution of cesium chloride used in Meselson & Stahl's DNA replication experiment?

Centrifugation involves separating particles of different sizes, masses, density and etc. In the experiment, the DNA macromolecules are suspended in a solution of cesium chloride gradient and then ...
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Can a hinge joint technically allow rotatory motion?

Let's use a hinge joint and pivot joint as examples. When talking about the difference between them in terms of movements permitted, I see that on any websites and textbooks, the term 'rotation' is ...
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Can bacteria be killed by purely physical trauma?

In a question over on Skeptics Stack Exchange, I half-jokingly listed "blunt force trauma" as a means by which a bacterium could be killed. That makes me wonder if it really is only a joke ...
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Question in gel chromatography experiment

Here I am trying to do gel chromatography to separate vitamin B12 and Bovine Serum Albumin (BSA) in this experiment, I am using sephacryl s-100 HR gel column my question is can I use Phosphate ...
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Can viruses be deformed?

Viruses are created in their fully-formed state and do not grow. But one thing has been bugging me lately: can a virus be deformed, e.g. in order to fit into an opening slightly smaller than itself? ...
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How do the biophysics of how cerebrospinal fluid mechanically protects the brain work?

The two mechanisms I've seen mentioned are the cerebrospinal fluid (CSF) acting as a hydraulic cushion or shock absorber, and how CSF creates a micro-gravity environment through buoyancy. I have very ...
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Can the eye determine which type of defocus is presented to it?

I have a question regarding myopic and hyperopic defocus. My question is, is the eye able to determine which type of defocus is presented to it and if so what mechanisms allow it to distinguish ...
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How would one model a Neutrophil Extracellular Trap with Hookean Springs?

This is a question based in biology but involves a good amount of physics. Given that a Neutrophil Extracellular Trap (N.E.T) behaves like an aggregate of DNA strands with citrullinated Histones and ...
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Biophysically, how to change from a tonically firing neuron to an occasionally firing one?

In terms of membrane properties, size and neuronal biophysics (assuming no change in incoming excitation), how can a tonically firing neuron become (say during development) an occasionally bursting ...
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Question about the Derivation of the cable equation for neurites

I read in Wikipedia how the cable equation was derived (here) and had a specific problem regarding one of its equation: At the start of the derivation it states that we first need to pretend that the ...
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Why the length constant of passive current flow isn't depend on the membrane capacitance?

I read that the equation for the length constant for passive conductance along a neuron depend on the resistance of the plasma membrane, the intracellular axoplasm and the extracellular medium. My ...
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Does the zeta potential of a nanoparticle generally take into account ligand charge?

For example, if I had a quantum dot nanoparticle with conjugated linker peptides capped with polyarginine tracts. Would the localization of negative charge from arginine change the zeta potential ...
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Why does constant current in electrophoresis mean that the molecule moves at the same rate? [closed]

Two part question: Part 1: I have always learned that when running a SDS-PAGE current is what decideds how fast the macro molecules migrate. However, if the force excerted on a molecule is equal ...
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What is the charge of (bacterial) ribosome?

Ribosomes are negatively charged and thus electrostaticaly repelled from DNA. However, I could not find a good reference that would allow me to estimate the magnitude of negative charge on a ribosome. ...
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Ion-gated ion channels

Today I've heard for the first time of calcium-gated ion channels but find it hard to get an idea how they work, where they are located, and which role they play. I assume calcium-gated ion channels ...
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How do signalling molecules find their receptors at large distances?

I have been baffled with this question approx. for a dozen of years for now. There is a default "lock & key" mechanism of action assumed for the interaction between a signalling molecule and its ...
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How does energy conversion happen (chemical to mechanical?) in moving body muscles?

From my understanding, the brain sends electrical pulses through neurons to different part of the body to initiate a movement. My question is, how is the movement realized? For example, in a train, ...
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How to include multiple DNAs into a crystal structure

I have a crystal structure (PDB 3OS1)that shows the interaction of PFV intasome with a substate DNA. I would like to replace the existing DNA in the intasome as well in the substrate with a longer ...
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Can enzymes be modeled using classical mechanics?

When enzymes interact with substrates (i.e. a small ADP molecule and the much larger ATP synthase), does quantum mechanics play a significant role? Or can the interactions be relatively accurately be ...
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Which proteins are most sensitive to electric fields?

Many Proteins have ionic charges that can attract each other (e.g. Formation of salt bridges) or repel each other. On the other Hand, Proteins are mostly immersed in water that screens most of the ...
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Does the Rayleigh formula apply to electron microscopes or only light microscopes?

I am asked to determine the resolving power of both a TEM (transmission electron microscope) and a SEM (scanning electron microscope) and given the Rayleigh formula below. $$Resolution=\frac{0.61\...
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Bioenergetics book

I already asked this question on the physics SE but redirected here: In the field of biophysics, it seems there is a subfield called "bioenergetics" about the processes of generating energy by ...
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Can UV radiation be safe for the skin?

It is well known that UV radiation can damage the DNA and generally harm our skin. We also know that UV radiation helps on the production of melanin and Vitamin D. From what I could find, the DNA ...
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"Straight" or "linear" helix

If an alpha helix is discontinued for a short while and then continues in a different direction, I prefer to call in "kinked". If the helix is simply uniformly following one direction, I prefer to ...
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What is the native structure of amyloid-beta protein under physiological conditions?

The amyloid-beta protein forms cross-beta structured fibrils. But under normal physiological conditions what is their predominant secondary structure. Is it alpha-helix, random coil or beta-sheet?
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Why is wound contraction very slow?

I am working on mathematical model for healing of dermal wounds. For anyone who's a bit familiar with Physics and Math, for the model I use the Cauchy Momentum Equation as a basis, and from there I ...
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Where does this equation in the electrophysiology literature form come from?

In my studies I keep coming across the form of an equation that is used in many different mathematical models for voltage gated ion channels. The most general form I have found is in the 1977 paper ...
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How many frames per second do human eyes see? [duplicate]

I observed when a helicopter rotor or fan is spinning the blades blur making it impossible to count the blades, but after a certain speed the blades seem to become visible making it possible to count ...
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How does nitrogen gas partial pressure change when ascending during scuba dive?

Scuba divers suffer decompression illness in which during sudden ascension, gas bubbles form in blood vessels and do not get reabsorbed quickly, leading to various problems including a stroke. The ...
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Entropy during neuronal signaling

to begin with: I have some background in cognitive neuroscience, but have not intensely studied the biochemical background of neuronal signalling, so please correct me if my basic understanding is ...
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Is there any independent non-DNA based information system in the cell

The information in protein is not neccessarily independent of the genome as the information of amino-acid sequence comes directly from the genome. The process of post-translational modification may ...
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Difference between prions and amyloid proteins?

Amyloid and prions are misfolded proteins, but what, if any, is the difference between them? Is amyloid a type of prion with a fibrillar structure?
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How to derive the deactivation time constant in this model of Acetylcholine Receptor state kinetics?

I came across this simple analytical expression of time constant of deactivation in Elenes et al., 2006. How does one derive this expression $$\displaystyle\tau_\text{deactivation}\approx\frac{1}{D_+ ...

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