quinta-feira, 25 de abril de 2013

60 anos da descoberta do DNA

DNA: the 'smartest' molecule in existence?

Composite image of zip, ladder, DNA strand, Morse code (courtesy Porthcurno Telegraph Museum) and telephone coil. Other images via GettyDNA is structured like a ladder, opens and closes like a zip, codes data like Morse code and coils tightly

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DNA is the molecule that contains and passes on our genetic information. The publication of its structure on the 25th of April 1953 was vital to understanding how it achieves this task with such startling efficiency.
In fact, it's hard to think of another molecule that performs so many intelligent functions so effortlessly. So what is it that makes DNA so smart?

Multi-millennial survivor

For such a huge molecule, DNA is very stable so if it's kept in cold, dry and dark conditions, it can last for a very, very long time. This is why we have been able to extract and analyse DNA taken from species that have been extinct for thousands of years.
Illustration of a woolly mammothScientists have 'resurrected' blood protein from preserved mammoths after harvesting their DNA
It's the double-stranded, double-helix structure of DNA that stops it falling apart.
DNA's structure is a bit like a twisted ladder. The twisted 'rails' are made of sugar-phosphate, which give DNA its shape and protect the information carrying 'rungs' inside. Each sugar-phosphate unit is joined to the next by a tough covalent bond, which needs a lot of energy to break.
In between the 'rails', weaker hydrogen bonds link the two halves of the rungs together. Individually each hydrogen bond is weak - but there are thousands of hydrogen bonds within a single DNA molecule, so the combined effect is an extremely powerful stabilising force.
It's this collective strength of DNA that has allowed biologists to study genes of ancient species like the woolly mammoth - extinct but preserved in the permafrost.
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This short animation explains everything else you need to know about DNA.

Clever facsimile machine

Our cells need to divide so we can grow and re-build, but every cell needs to have the instructions to know 'how to be' a cell.

Intelligent error correction

Brain Zip
The consequences of wrongly read or copied information can be disastrous and cause deformities in the proteins.
So as DNA replicates, enzymes carry out a proof-reading job and fix any rare errors.
They tend to repair about 99% of these types of errors, with further checks taking place later.
DNA provides those instructions - so a new copy of itself must be made before a cell divides.
It's the super-smart structure that makes this easy. The 'rungs' of the DNA ladder are made from one of four nitrogen-based molecules, commonly known as A, T, G and C. These form complementary pairs - A always joins with T and G always joins with C.
So one side of the double-stranded DNA helix can be used as a template to produce a new side that perfectly complements it. A bit like making a new coat zip, but by using half of the old zip as a template.
The original side and the new one combine together to form a new DNA double helix, which is identical to the original.
Cleverly, human DNA can unzip and 'replicate' at hundreds of places along the structure at the same time - speeding up the process for a very long molecule.

Molecular contortionist

coiled telephone cordTwo metres of DNA coils like a telephone cord to fit into each cell
DNA is one of the longest molecules in the natural world. You possess enough DNA, stretched out in a line, to reach from here to the sun and back more than 300 times.
Yet each cell nucleus must contain two metres of DNA, so it has to be very flexible. It coils - much like a telephone cord - into tight complex structures called chromatins without corrupting the vital information within.

DNA bases - vital rungs in the ladder

There are four different nucleotide bases in each DNA molecule:
  • Adenine (A)
  • Thymine (T)
  • Guanine (G)
  • Cytosine (C)
These small molecules join DNA together and encode our genetic information.
And despite being packed in so tightly, the genetic material can still be accessed to create new copies and proteins as required.
Human cells contain 23 pairs of chromosomes, with each containing one long DNA molecule as well as the proteins which package it. It's no wonder DNA needs to be extremely supple.
Amazingly, this folded and packed form of DNA is approximately 10,000 times shorter than the linear DNA strand would be if it was pulled taut.
This is why we have the 'luxury' of having the plans for our entire body in nearly every cell.

Biological database

DNA storage

Morse code
research team has encoded data in artificially produced segments of DNA, including:
  • A 26-second snippet of Martin Luther King's classic anti-racism address from 1963
  • A .pdf" of the seminal 1953 paper by Crick and Watson describing DNA' structure
The total data package was equivalent to 760 kilobytes on a computer drive. Physically, the DNA carrying all that information is no bigger than a speck of dust.
Genes are made up of stretches of the DNA molecule which contain information about how to build proteins - the building blocks of life which make up everything about us.
Different sequences of the four types of DNA bases make 'codes' which can be translated into the components of proteins, called amino acids. These amino acids, in different combinations can produce at least 20,000 different proteins in the human body.
Think of it like Morse Code. It too uses only four symbols (dot, dash, short spaces and long spaces), but it's possible to spell out entire encyclopaedias with that simple code.
Just one gram of DNA can hold about two petabytes of data - the equivalent of about three million CDs.
That's pretty smart, especially when you compare it to other information-storing molecules. Using the same amount of space, DNA can store 140,000 times more data than iron (III) oxide molecules, which stores information on computer hard drives.
DNA may be tiny but with properties including stability, flexibility, replication and the ability to store vast amounts of data, there's a reason why it must be one of the smartest known molecules.
With huge quantities of data being produced by ever-growing computer systems, traditional data storage solutions, like magnetic hard drives are becoming bulky and cumbersome. Researchers have now used DNA to store artificially-produced information, but could this be the future of data storage?

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