Tag Archives: Life and Light

Light and Life – Part 3

This VERITAS was written on Tuesday, May 30, 2006
                      
Friends,

       This is part III of the VERITAS series in which we study the complex relationship between light and life.

       In the last VERITAS( MYSTERIES OF THE BRAIN : Part 14 , 19 May 2006) we saw that Adenosine and Melatonin are chemicals that make us tired and want to go to sleep and then help us sleep as long as there is darkness. Today we will understand Melatonin in detail and this will help us understand our body’s important relationship with darkness and night.

                   Swiftly walk over the western wave,
                   Spirit of Night!
                   Out of the misty eastern cave,
                   Where, all the long and lone daylight,
                   Thou wovest dreams of joy and fear,
                   Which make thee terrible and dear,-
                   Swift be thy flight
                                    – Shelly  ( “To the Night”)

       Melatonin is a harmone that promotes sleep. If this harmone is present in a greater quantity we feel more sleepy and if this harmone is
present in a lesser quantity then we feel less sleepy. This harmone is present in highest quantity in our bodies at night. This harmone is a part
of the system that regulates our circadian system( our internal system of light and darkness and therefore of time ).

       This harmone is present in nearly all creatures. Even simple creatures like algae have this chemical and this shows that nearly all creatures use Melatonin to regulate their body clocks. In some creatures Melatonin levels decides their skin colour which changes at night to prevent them from getting noticed by predators. Some animals use Melatonin levels to regulate their breeding patterns.

       In humans and other higher mammals Melatonin is produced in the pineal gland in the brain and the retina( in the eyes). This production is
controlled by the suprachiasmatic nucleaus in the hypothalmus ( called SCN). SCN is the primary controller of the circardian cycle. The SCN takes input about the presence or absence of light from the eyes and controls the production of Melatonin.

       AS humans we tend to hate the concept of darkness except when we sleep. We associate darkness with evil and fear. We associate light with hope and joy. In olden days when we did not have artificial light our bodies were exposed to longer periods of darkness. Now our brightly
illuminated homes and streets means that our exposure to darkness has become much lesser. We have banished darkness from our lives! Is that a good thing?!

       No, it is not! If our bodies are exposed to less darkness we have lesser Melatonin production in our bodies. And this does not just mean
that perhaps we are not sleeping as well as we were in the olden days. It means that our immune system is weaker, it means that we have more chances of cancer and it means that our resistance to stress is much less than our “unilluminated” ancestors!!!

       Research has shown that melatonin boosts the immune system. It does that by enhancing the production of T cells. Doctors administer
Melatonin sometimes to enhance the immune system of patients.

       Melatonin is a very powerful antioxidant. It reduces the damage to cells from the hydroxyl radical(OH) by neutralizing it. If the body has enough Melatonin then the damage to brain cells because of ageing is reduced. In tests on mice scientists found that mice with enough melatonin tend to live upto 20% longer. And this may be bacuse of their brains and immune systems being protected from these free radical attacks by the antioxidant properties of Melatonin.

       Research has shown that Melatonin prevents the damage to body cell DNA from carcinogens. Carcinogens are chemicals that damage the cell’s genetic code and may cause the cell to multiply endlessly like crazy – a condition known as cancer. For example benzene is a carcinogen and causes blood cancer. Melatonin prevents these carcinogens from damaging the cell DNA and thereby prevents cancer. Lack of enough Melatonin exposes you to more cancer risk. There is evidence of greater cancer incidence amoung people who work in light at night and sleep during the day. These people never get a chance to produce enough Melatonin. So Melatonin protects you from the cancer causing effects of chemicals and radiation.

       So we see that darkness of the night is not such a useless thing. It is not evil. It is not a sign of despair. It is very important so that we may produce enough Melatonin in our bodies. Thus it is not just important to sleep, it is very important that we get enough sleep and we get enough darkness at night!

          When from the clock’s last chime to the next chime
          Silence beats its drum
          And Space with gaunt grey eyes and her brother Time
          Wheeling and whispering come
          She with the mould of form and he with the loom of rhyme.

          Then twittering out in the night my thought birds flee,
          I am emptied of all my dreams:
          I only hear Earth turning, only see
          Ether’s long bankless streams,
          I only know I should drown if you laid not your hand on me

                                        -James Flecker (“Silence”)

Kanwar

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 Go, wondrous creature! mount where Science guides:
 Go, measure earth, weigh air, and state the tides:
 Instruct the planets in what orbs to run,
 Correct old time and regulate the Sun;
|======================================================|

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Veritas by Kanwarpreet Grewal is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

Light and Life – Part 2

This VERITAS was written on Thursday, May 12, 2005

 

Friends,

       This is part II of the VERITAS series in which we try to understand the complex relationship between light and life. In today’s part we will try to understand how light from outside us can create the sensation of vision. We will not try to understand the eye in detail. Our aim today is to understand the moment when the physics of the photon(particle of light) causes a biological(or chemical) sensation in our eye.

       The innermost layer of the eye is retina. The retina contains two kinds of cells: the rods and the cones. The rods help us see in low light.
And the cones help us perceive colour. The rod and cone cells contain a chemical called rhodopsin. This chemical is photosensitive. Rhodopsin is composed of two chemicals: scotopsin and 11-cis-retinal. Retinal is also called retinine. It looks something like this:

<something>-C=C-C=C-C=C-C=C=O
               | |
               H H

       We have written <something> for the part that does not interest us. The part that interests us is a series of Carbon atoms(written as C)
with alternate double and single bonds. The double means that there is an extra electron there. We have represented a double bond as = and a single bond as – . When a photon of light strikes the above molecule the electron in the double bond gets bumped. So for a short time the double
bond gets converted to a single bond. This allows the Carbon atoms to rotate. The molecule gets converted to something like this:
                 H
                 |
<something>-C=C-C=C-C=C-C=C=O
               |
               H

       There is no difference except the structure. The C-H have rotated. AFter rotation the double bond gets formed again and the C-H are locked in this new position. All this takes about 10 pico seconds.

      http://www.elmhurst.edu/~chm/vchembook/images/533cistransretinal.gif

The main point is that when 11-cis-retinal absorbs light its structure changes to form all-trans retinal. This creates an electrical impulse which is transmitted to the brain.

       11-cis-retinal and all-trans retinal are isomers: different structures of the same molecule.

       So we see that the retinal is very important for the sensation of light. How do we produce retinal? We dont!!!! We have to eat it! Vitamin A
gets convetred to retinal. Actually vitamin A looks just like retinal we showed above. There is just a extra Hydrogen atom which is removed by the body. It is extremely important that you eat your Vitamin A. Otherwise you could become blind when the number of photons around you are less (Night Blindness). So eat your carrots!

Media_httpwwwelmhurst_cwgyj

        Now we have seen when retinal gets hit by a photon the double bonds get bumped and that creates an electric sensation of light which is
transmitted to the brain. Chemically we say that when 11-cis-retinal gets hit by a photon it gets converted to all-trans retinal. But what happens when all 11-cis-retinals get converted? It never happens. There is a reverse process too. Very soon the all-trans retinal gets converted back to 11-cis-retinal. SO there is never a lack of the 11-cis-retinal. This reconversion of all-trans retinal to 11-cis-retinal happens very fast and it is a spontaneous process. It happens because all-trans retinal is a unstable molecule and 11-cis-retinal is a stable one.

       Friends! We have understood it! We have understood the process of the sensation of light. But have we? We have not. We have only understood the process, or the “how”. We have not understood the “why” of it. We should we have a vision at all? Why only retinal and not some
other chemical? Why only photons? These are the questions that we may never find answers to.

       I often use the example of a group of apes. Take a clock and throw it to a set of apes on an island. The apes will be very curious about the clock. They will try to understand it. After years of effort they will realize that it has a pattern: The clock hands move round and round. Centuries later… after several generations they may have invented numbers and they will know that for 12 rotations of the long hand the small hand moves one step. But it will take them a millions of years to discover the true meaning of the clock. Because to understand the true meaning they will have to discover the concept of time! And till they discover that concept their knowledge is merely a collection of facts. Why did this happen? This happened because the apes were trying to understand something created by a superior intellect. They would have to reach a superior intellect before they can understand the true meaning. COllection of facts is easy. Understanding the meaning is difficult.

       We find ourselves in a similar position. We are trying to understand a Universe created by a “superior intellect”. And we are struggling to understand it. Our intelligence would have to reach that of the Creator himself before we really understand. Till then we will have to be content with “collecting mere facts”.

Kanwar

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=========================|
 Go, wondrous creature! mount where Science guides:
 Go, measure earth, weigh air, and state the tides:
 Instruct the planets in what orbs to run,
 Correct old time and regulate the Sun;
|======================================================|

Creative Commons License
Veritas by Kanwarpreet Grewal is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

Light and Life – Part 1

Media_httpchandraharv_xglaa

This post was written on Wednesday, February 02, 2005

Friends,

       Today we are starting a new series in VERITAS. Just like our “Mysteries of the Brain” series this series will last for several months(or years!). In this series we will explore the complex relationship that life has with light.

       If we examine our senses and pick one that is the most important we would no doubt pick sight. All other senses are local in range. We have
to be near something in order to touch,smell or hear or taste it. The range of these four senses is very limited compared to the range of sight.
We can see the moon and stars( which are millions of kilometres away)!

       But what is sight? It is to detect light and to be able to get information about things from which this light comes. But what is light?
It is an electromagnetic wave( a wave with an electric and a magnetic field moving perpendicular to each other). So seeing means to detect
photons( particles of light). It seems like a very complicated thing to do.

 In today’s VERITAS we will try to understand how the sense of sight evolved. Light had always existed in this world. But when did the first
living thing realize that there is something( a em field) around it which it can use to detect the shape and size of things without touching it? And
how did this realization evolve into something as complicated as the eye?! So how did the first blind creatures realize light???!!!

       When Darwin proposed his theory of evolution he realized that the eye would be very difficult to explain in terms of evolution. Indeed, the
creationists ( people who do not believe in evolution. According to them the world was created by a Supreme Being. This world is a perfect world-
No need to evolve) frequently use the example of the eye to state their point. They say that the eye could not have evolved from something
simpler. And this is because the eye is something so complicated and several complicated parts come together to make the functional eye.
Any one part of the eye is useless without the other. SO the creationists believe that any one part could not have given the bearer of this part any
advantage in terms of survival. So this part could not have evolved into the eye!

 But people who believe in evolution have an answer to these. And in recent years a lot of scientific evidence has shown that the eye did evolve from something much simpler.

       Lets go back to  the Cambrian period( about 550 million years ago). The world is full of primitive creatures that feed on other creatures. Predation has started. SOme creatures are the prey and the others are predators. But none of them can see. They touch each other and
decide to eat or move away. One of these creatures develops a small light sensitive cell( out of nowhere! Mutation! He was just born with it). That
one cell gives this creature a small sense of light or darkness. He gets a slight advantage in terms of survival. This creature passes on this trait
to its offspring. They too get this survival advantage. Slowly after several hundreds of generations this light sensitive cell becomes a group
of light sensitive cells. Organisms that have this group get a survival advantage over the ones who have lesser number of cells. And then
after generations a hole of light sensitive cells is formed which gives a much better idea of not only light and darkness but also relative
brightness. Then in some creatures this hole is filled by a liquid that bends light to form a blurred image. And much much later a lens is formed
that can focus to form a sharp image by bending light. That is how the eye evolved. So each generation that had the additional light sensitive apparatus had a slight survival advantage over the creatures that did not have this apparatus. Scientists have found fossil records of each of these stages.

       How much time would this evolution from a light sensitive cell to a primitive eye take. According to a group of scientists( Nilsson and Pelger)
this would take no more than 400,000 years( assuming a generation lasts for 1 year as it is in case of fish). So the eye has had a lot of time to
evolve since the first light sensitive cell appeared(550 million years ago)

       But there are several questions that I still dont know the answers to:

a) Why was detection of light(photons) a survival advantage. Why not detection of say electrons/atoms? Why didnt a creature with a electron
  sensitive cell not survive and evolve?
b) How is the detection of light actually done by the eye? Is it a photoelectric thing ?

c) We can detect only a small range of frequencies of light. Why only  these? Did evolution decide something here?

   If I find any of the answers to these questions I will post them in a future part of our VERITAS series “Light and Life”.

Friends, see how such  complicated things as the eye can evolve out of almost nothing over millions of years. The people who dont believe in
evolution dont do so because they are overwhelmed by the complexity of the living organisms. And they cannot understand how something as simple as evolution explain  this. But dont underestimate the power of a million years. It is a  VERY VERY long time. Our life spans are nothing compared to this. And things do change in a million years.

        To appreciate our sense of sight lets recall the sonnet that Milton wrote after he became blind. In this sonnet Milton tries to come to terms with his lack of vision:

    When I consider how my light is spent
    Ere half my days in this dark world and wide,
    And that one talent which is death to hide
    Lodg’d with me useless, though my soul more bent
    To serve therewith my Maker, and present
    My true account, lest he returning chide,
    “Doth God exact day-labour, light denied?”
    I fondly ask. But Patience, to prevent
    That murmur, soon replies: “God doth not need
   Either man’s work or his own gifts: who best
   Bear his mild yoke, they serve him best. His state
   Is kingly; thousands at his bidding speed
   And post o’er land and ocean without rest:
   They also serve who only stand and wait.”

Kanwar

|=============================

=========================|
 Go, wondrous creature! mount where Science guides:
 Go, measure earth, weigh air, and state the tides:
 Instruct the planets in what orbs to run,
 Correct old time and regulate the Sun;
|======================================================|

Creative Commons License
Veritas by Kanwarpreet Grewal is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.