On Diffraction and the Helical structure of DNA

This is the famous Photograph 51, which is the nickname given to an X-ray diffraction image of crystallized DNA taken by Raymond Gosling in May 1952.

Crick and Watson used the features of this photograph to develop the chemical model of the DNA molecule aka Double-helix.


A simple way to understand why a helix structure produces such a diffraction pattern is to take a spring of a ballpoint pen and illuminate with a laser pointer.


Image courtesy of D. Tierney and of H. Schmitzer, Xavier University in Cincinnati


Although the spring is not a Double Helix structure, the diffraction pattern produced as you can see  is very similar to the famous Photo
51 of helical DNA. 

It was also known at that time that DNAs obeyed the Chargaff’s rules: Adenines paired with Thymine and Guanosine  paired with


As James Watson explains in this video,
he was trying out different models for the DNA that satisfied
Chargaff’s rules and also the Helical structure of DNA as Gosling had found out. This led him to the Double Helix model of DNA.

And this model has stood the test of time. In 2012, an electron microscope  captured the famous Watson-Crick double helix in all its glory asserting that the DNA is indeed a Double Helix.


                              Electron microscope image of DNA

The story of the discovery of DNA and its study is captivating by itself and here’s a list of useful papers and web links if you like to venture more:

 –  Nature podcast of Raymond Gosling discussing the Photograph 51.

–  How Rosalind Franklin Discovered the Helical Structure of DNA: Experiments in Diffraction

  The DNA Double Helix Discovery — HHMI BioInteractive Video (Includes discussion with Dr.James Watson)

How we discovered DNA – TED talk by James Watson

The Discovery of the DNA Double Helix – A historical overview

Have a good one!

De-constructing Backyard Brain’s TED talk

** Images of dead animals ahead and reading this post sort of ruins the magic from the demo *** SPOILER ALERT

With over 2M hits on YouTube, this TED talk by Greg Gage from Backyard Brains was my one of my first insights into neuroscience. He demonstrates how to control someone’s hand with your brain.

As a maker and not knowing much about Neuroscience, me and my friends tried to replicate the same with some DIY kits but it failed. But why?

How to force muscle movement ?

Now with the help of some friends who actually study neuroscience,we were able to decipher the talk. The talk is subtle and doesn’t dwell into some technicalities which are essential to recreate the experiment.

Give a shock and muscles will twitch. This was known to scientists as early as 18th century through the experiments conducted by Galvani and Volta.


                             Source: Academy of 21st century learning

Now you know that in order to make the legs of an organism twitch, you have to administer a shock to the right nerve.

EMG (Electromyograph)

An electromyograph detects the electric potential generated by muscle cells when these cells are activated. A typical processed signal from a EMG looks like so.


                                    Source: Backyard brains

From looking at the data, the signal peaks when the hand is squeezed.
We set a threshold limit (T) beyond which it implies/ triggers that the hand has moved.

Now with a simple piece of code, you can administer a shock every time this threshold limit is passed and do whatever you want.

Here’s the legs of a frog being controlled by the hand:


                                      Source: anasjaber

How to control someone else’s arm with your brain ?


You need a device that takes in the EMG from one person and constantly looks out whether the threshold limit has passed.

If it did, a current stimulates the muscles of the other person and causes it to move. And that’s how you “control someone else’s arm with your brain.”

Have a good one!

* Electrical muscle stimulation for stroke recovery(video)

** Functional electrical stimulation

** We are by no means neuroscientists and have huge respect for the work done by Greg and his team at Backyard Brains. This post is not meant to undermine the work but to bring out the subtleties that belies it.

A twist in the tale – Spider silk


If you have tried to suspend a piece of article on rope then you will realize that
its hard to make it stationary without rotating about the center .

This is due to the elastic
nature of the rope(torsion), where upon deformation the rope would like to return
back to its initial state.


Now with most fibers you will witness the same torsional damped oscillations about the original position.

But if you spend time observing a spider, you will see that a spider does not seem to be facing this problem. It seems to be relatively stable when hanging on its thread. 

How is it doing that ?


Well, in a recent paper researchers explored this and found out that the spider was able to accomplish this by undergoing a plastic deformation that dissipates the applied energy in the thread.

It is speculated that the energy is lost due to friction between the fibers of the silk (which are linked by hydrogen bonds),

This drastically dampens the rotational motion of the spider making it ready to face its prey heads on.

Have a great day!

** You can read the paper here.

I like your post on spider web. Did you know it is also stronge than kevlar

Whenever a comparison is made between the strength of spider silk and kevlar, the most common question that is asked is:

If it is so strong, then why can I punch through it ?


First thing to understand is that If you take steel wire/fiber or kevlar to be as thin as a spider silk, you would also be able to punch through it. 

And as far as testing goes:

You take strands of spider silk; weave it into a rope with the same girth as a steel cable. And then you compare the strengths of the two materials.


The results of these tests have concluded that indeed the tensile strength of spider silk is stronger than Kevlar.

Or if you like a DIY backyard version to test it out for yourself can follow this video by ‘Every kind of scientist’

Also here’s a TED talk that talks a great deal about the strength of spider silks.

Thank you for asking/submitting and have a good one!

* You can also ask questions and share your views on twitter- @fyphysica

** How does a spider spins its web?

It’s easy:  Form a triangle, then a hexagon, then a bicycle wheel

This is the general mechanism on how a spider spins its web (talk about engineering, right?). When an insect gets caught in its web,
the vibrations caused by the insect is felt by the spider which then
rushes to engulf its prey.

Now here is the trippy part ; This is the effect of drugs on the pattern of the web.


Hope you are having a great week. Have a good one!

* Spider spinning a web (video) (if you find a better full video let us know)

** Spiders on drugs –  NASA article ; Video

Birth: The moment of creation


To witness the birth of a child is our best opportunity to experience the meaning of the word miracle

– Paul Carvel

In a matter of a few minutes, a baby goes from a liquid (called as amniotic fluid) breathing environment to that of air. And in this time frame, a whole lot of things have to go right.

‘Lung Detergent’/Surfactant



Somewhere between the 24th and 28th week of the pregnancy, surfactant
– sometimes called “lung detergent” – starts being produced in the
amniotic fluid. As the pregnancy continues, more surfactant is produced.

That is why the closer to term, 38 to 40 weeks, the better a baby is
able to breathe outside the womb.

What is a surfactant ?

Surfactants are essentially
chemicals that reduce the surface tension of the fluid. (or) It is a
chemical that reduces the stiffness of a balloon.

If you reduce
the stiffness of the balloon, I think from personal experience you can
understand the breathing in becomes a lot easier!


Why is the surfactant important in the lungs?

Surfactant coats the inside of the lungs and keeps the alveoli, or air sacs, open by keeping them at the right pressure.

RDS ( Respiratory Distress Syndrome )  

Babies that are born before prematurely do not have much of this surfactant in their lungs and as a result can suffer from something known as RDS – Respiratory Distress Syndrome.


               A – Alveoli of a baby with RDS         B – Healthy alveoli

With less surfactants in their lungs, some of the alveoli collapse due to the excess pressure.

If you remember this post on ‘Smaller Bubbles, Higher Pressure’, then you might know that the balloon with the smaller radius has the higher pressure and therefore collapses.


This is exactly what happens in the lungs of babies born prematurely as well, many of their alveolus collapse.

With less alveoli available, the infant has to work hard to breathe. He or she might not be able to breathe in enough oxygen to support the
body’s organs. The lack of oxygen can damage the baby’s brain and other
organs if proper treatment isn’t given.

Common Treatment

Babies who have RDS are given surfactant until their lungs are able to start making the substance on their own.

That’s how simple physics blends with biology to yield elaborate ecstatic phenomenon that gears life. Have a great day!

Dedicated to my friend – SM!

Sources and extras

Agpar score

More about RDS

That’s Electrooculography!

The eye is a basically a dipole ( a separation of electric charges )

It was observed by Reymond in 1848 that the cornea of the eye is electrically positive relative to the back of the eye.This potential was surprisingly not dependent on the amount of light falling on the eye.


                The cornea is the transparent front part of the eye

Dipoles and Eye Tracking

This means that as the eye moves from side to side, the dipole moves as well. To capture the movement of the dipole, one places two electrodes on both sides of the eye. ( like the one placed on this guy )


If the eye moves from the center position to the right, one of the electrodes becomes slightly positive and the other negative. This leads to a spike in the positive direction.



And if the eye moves from the center position to the left, the polarity of the electrodes reverses. This leads to a spike in the negative direction.


That’s about it. That’s EOG for you all. I hope you guys enjoyed this post.

Have a great day!


Sources and Extras:

More about EOG

Gif source : The backyard brains