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DNA - The Origin Of Life

Updated on September 24, 2013

Discovery and Pictures of DNA

In 1953 James Watson and Francis Crick, with help from Rosalind Franklin and Maurice Wilkins who were doing their own research in London, discovered the double helix structure and the function of DNA. Watson, Crick and Wilkins shared the Nobel Prize for Medicine in 1962 but sadly Rosalind Franklin had died in 1958 and, despite her key experimental work, could not receive the prize.

Now, 60 years later, the first ever picture showing the double helix structure of DNA has been taken. The image was taken by Enzo di Fabrizio from the University of Genoa, Italy. Fabrizio propped up a section of DNA, taken from a diluted solution, between two nanoscopic silicon pillars and shone electron beams through tiny holes at the base of the 'pillar' to create a high resolution image.

What is DNA?

DNA, short for Deoxyribonucleic Acid, is a molecule that holds the genetic instructions used in the development and functioning of all known living organisms. DNA is a macromolecule that is essential for all life. Most DNA is located in the nucleus of the cell, but a small amount of DNA can also be found in an organelle called the mitochondria.

The information that's in DNA is stored as a code consisting of four chemical bases:

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T)

Human DNA consists of about 3 billion bases, around 99% of which are the same in all people. It is the order of the sequence that determines how the organism is 'built'.

What Is RNA?

RNA stands for ribonucleic acid and is an important molecule with long chains of nucleotides. RNA molecules are sometimes involved in the transmission of genetic information but its main function is to transfer the genetic code needed for the synthesis of proteins, from the nucleus to the ribosome.

Much like DNA, RNA is made up of bases but instead of the chemical base Thymine RNA has the base Uracil. Therefore the 4 bases in RNA are:

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Uracil (U)

Nucleotides

Nucleotides are the monomers of nucleic acids (DNA or RNA) and they consist of:

  • One phosphate group
  • One 5 carbon sugar molecule
  • One organic nitrogenous base.

These 3 subunits are joined by a covalent bond to form a single nucleotide molecule. The phosphate group in all nucleic acids are the same and the sugar molecule is the same in DNA (deoxyribose) and RNA (ribose).

A condensation reaction between the phosphate group of one of the nucleotide and the sugar of the other nucleotide will join the two nucleotides together. They bond together to form long 'backbones' or chains which is then called a nucleic acid. The organic bases project from the chain. It is the sequence in which these nucleic acids bond that determines the coded information that the nucleic acid holds. Only nucleotides with the same sugar molecule will bond - this means that you will either get the nucleic acid DNA or RNA.

Pyrimidines

Bases

Organic bases are categorized under one of two categories.

The Purines:

  • Adenine
  • Guanine

The Pyrimidines:

  • Thymine
  • Uracil
  • Cytosine

A DNA molecule forms when two strands of polynucleotide molecules come together and twist to form what looks like a ladder.

The two DNA strands will run parallel with each other because the space between them is taken up by the bases that stem inwards.

On one of the chains where a pyrimidine appears the other chain will have a purine. More importantly, where there is a adenine base on one chain the other chain will have an thymine base and when there is a guanine base there will be a cytosine base on the other chain.

As the strands come together hydrogen bonds will form between the complementary bases (A with T and G with C) and then the two chains will twist to form the double helix that we are all too familiar with today!

For any biology A-Level students, here are some more useful hubs!

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