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Replication

The DNA molecular structure resembles a zip fastener, where each tooth can be any of four molecular bases.  The bases G-C and A-T are each small organic molecules that at one point are covalently bound to a triphosphate (containing three phosphorous atoms) and a sugar group that binds them in a ribbon.  At their free end Guanine is attracted to Cytosine, with triple hydrogen bonds, and Adenine is attracted to Thymine, with double hydrogen bonds. 

In the following notation: black = Carbon;  blue = Nitrogen;  red = Oxygen; white = Hydrogen.   Bars joining them indicate a covalent bond, an electron shared between the atoms.  A double bar indicates two shared electrons.   

 

Cytosine  Cytosine (C4H5N3O) has a shape that attracts (fits)  Guanine Guanine (C5H5N5O) 


but not  Thymine Thymine (C5H6N2O2)  or  Adenine Adenine (C5H5N5), that attract (fit) each other.

 

Each of these bases is bound to a ribbon of  sugar molecules and at its other end lightly bonds to a matching base on the other half of the 'zipper' such that when it is 'unzipped' each attracts its opposite number (like magnets attracting the opposite pole) thus recreating a new matching half in the same sequence.

 

DNA replication.
DNA replication. 

 

This unzipping and reforming is called self-replication. It is going on continuously in all living things as new cells are created to replace those that die. In an adult human around three quarters of a million of our cells divide every second.  This cell division is the process we call organic life and may continue (usually briefly) after we are legally (brain) dead.

Other chemical mechanisms within the cell translate the genetic information stored in the DNA sequence to manufacture the proteins from which new cells are built and differentiate themselves, organising to become our various organs and to thus arrange themselves to form a human; and not a gorilla or a crocodile or a kola or a rose or a cabbage. The human genome project had now identified 32,185 human genes.

Accurate reproduction is very important to the viability of an organism.  Just as: 'WOLF' does not have the same meaning as 'FOWL' the location and order of sequence G-A-T-C within a particular DNA string (chromosome) will result in a different outcome to the sequence C-A-G-T .   And this difference will influence cell structure and purpose:   'The wolf eats the fowl' has a totally different meaning to: 'The fowl eats the wolf'.

This method of storing and reproducing instructions and data is twice as efficient as the binary method we presently use in electronic devices.  For example the binary processor in your computer or reading device requires each character in in each word in this sentence to be encoded in two bytes (each of 8 characters or bits).  In other words 16 ones and zeros are required for every character on this page (eg 'a' = 0000000001100001) and a similar number for each pixel in a simple colour image.  But DNA can encode the same information (sufficient for every unique character and symbol in every language in the world) in just eight characters.

There are a fraction over 3 billion characters in the human genome (3,079,843,747 base pairs).  In computer terms this is equivalent to about three quarters of a gigabyte of information storage. The same data is stored in the nucleus of each of our cells.  This is in nuclear DNA, before taking into account separate, but smaller, storage in each of the mitochondria (see below). 

A 'gig' isn't much you might say (less than $1's worth) but the actual data storage density is in excess of anything offered by our present electronic technology.  Cells are a lot smaller than the chip in a memory stick - there around a billion cells per cubic centimetre in hard tissue.

This also points to another reality.  Had not this replication chemistry been available, and the conditions for the reactions been just right, life could not have occurred in its earthly form. 

Life relying on another replication method that was say binary would be at a disadvantage and would have to use different replication mechanisms.  If there was a chemistry, at different temperatures and chemical concentrations, allowing say six base pairs it would be different again.  We and our cousins (the other animals, plants and other organisms) that are all descended from the original replicating cell (LUCA - see above) are here because the conditions on Earth were and are just right for our kind of life to prosper.

Elsewhere in the universe it may be different.

 

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Travel

More Silk Road Adventures - The Caucasus

 

 

 

Having, in several trips, followed the Silk Road from Xian and Urumqi in China across Tajikistan and Uzbekistan our next visit had to be to the Caucuses.  So in May 2019 we purchased an organised tour to Azerbaijan, Georgia and Armenia from ExPat Explore.  If this is all that interests you you might want to skip straight to Azerbaijan. Click here...

Read more: More Silk Road Adventures - The Caucasus

Fiction, Recollections & News

Peter Storey McKie

 

 

My brother, Peter, is dead. 

One of his body's cells turned rogue and multiplied, bypassing his body's defences. The tumour grew and began to spread to other organs.  Radiation stabilised the tumour's growth but by then he was too weak for chemo-therapy, which might have stemmed the spreading cells.

He was 'made comfortable' thanks to a poppy grown in Tasmania, and thus his unique intelligence faded away when his brain ceased to function on Sunday, 22nd May 2022.

I visited him in the hospital before he died.  Over the past decade we had seldom spoken. Yet he now told me that he often visited my website. I had suspected this because from time to time he would send e-mail messages, critical of things I had said. That was about the only way we kept in touch since the death of his daughter Kate (Catherine). That poppy again.  

Read more: Peter Storey McKie

Opinions and Philosophy

Electric Cars revisited (again)

  

Electric vehicles like: trams; trains; and electric: cars; vans; and busses; all assist in achieving better air quality in our cities. Yet, to the extent that the energy they consume is derived from our oldest energy source, fire: the potential toxic emissions and greenhouse gasses simply enter the atmosphere somewhere else.

Back in 2005 I calculated that in Australia, due to our burning coal, oil and sometimes rural waste and garbage, to generate electricity, grid-charged all-electric electric cars had a higher carbon footprint than conventional cars.

In 2019, with a lot of water under the bridge; more renewables in the mix; and much improved batteries; I thought it was worth a revisit. I ran the numbers, using more real-world data, including those published by car companies themselves. Yet I got the same result: In Australia, grid-charged all-electric cars produce more greenhouse gasses than many conventional cars for the same distance travelled.

Now, in the wake of COP26, (November 2021), with even more water under the bridge, the promotion of electric cars is back on the political agenda.  Has anything changed?

 

Read more: Electric Cars revisited (again)

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