The nucleotides of DNA join in the following structural configuration:

- - - hydrogen bond

H N N -- H - - - - O CH2
\ // \ / \\ /
C C -- C C -- C
\ // \\ / \
N -- C N - - - - H -- N C -- H
\ / \ /
N == C C -- N
adenine \ / thymine

H N O - - - - - H -- N H
\ // \ // \ /
C C -- C C -- C
\ // \ // \\
N -- C N -- H - - - - - N C -- H
\ / \ /
N == C C -- N
\ //
guanine N -- H - - - - - O cytosine

Beginning in the nucleus, the DNA molecule of the eukaryotic cell will be transcribed. The enzyme RNA polymerase separates the two strands of DNA and attaches the complementary nucleotides. The section of DNA being transcribed is the transcription unit. The RNA grows in a 5' to 3' direction. The initiation site for RNA synthesis is bound to by RNA polymerases. The promoter is the initiation site, and nucleotide sequences that RNA polymerase need transcription factors (specific proteins) to recognize. After the enzyme reaches the segment that is a termination signal, it stops adding nucleotides. This primary transcript is then processed to be functional mRNA. The ends are modified to protect, lengthen, and help the strand be recognized. A 5' cap of guanine and a Poly (A) cap (added to the 3' end) of adenine are attached. This messengerRNA now leaves the cell to give the message from the DNA to make polypeptides.

Translation occurs with the transferRNA (tRNA). It goes to the aminoacyl-tRNA synthetase, which joins an amino acid to its specific tRNA. The initiation is where mRNA, the tRNA with the first amino acid, and the two subunits of a ribosome come together. The mRNA molecule is in triplets known as codons. The tRNA matches up complementary triplets of anticodons. Elongation occurs with codon recognition where hydrogen bonds form with the mRNA codon and the tRNA anticodon. Then a peptide bond forms so that the new polypeptide is added to the growing chain. Translocation occurs so that the tRNA goes to the exit site and then leaves. Once the tRNA codes for the terminating (or stop) codon, elongation stops. The chain of amino acids then goes where it needs to (e.g. with others, an organelle, etc.)

A deletion or addition in DNA nucleotides would throw off the reading frame. Wrong triplets will be formed, and the wrong amino acids will be coded for. This would form an incorrect polypeptide chain and mess things up. A substitution in one of the nucleotides might not be as bad. It would only mess up its particular triplet. Even then, wobble may allow the tRNA to still code for the correct amino acid and there wouldn't be a problem.

P.S. Yes, this is all me...

Now, for something completely different in this node -- this time somewhat more useless. Next is a Python script to calculate a DNA sequence for any stream given in standard input.
import sys
g = ('a','c','g','t')
gencode=lambda x:[ sys.stdout.write("%s%s%s%s "%(g[int(ord(y))/64],\
                   for y in tuple(x)]

if __name__ == "__main__":
  while 1: 
   try: gencode(raw_input())
   except: break 

Example session:

$ ./ <

agat agac agtt ctcc ctat ctag agtt cgag cggc cgtg agtt ctaa
ctgc ctca cgga cgtt cgtg cggc cgtc ctaa cgtt ctag ctca agaa
ctat ctgc ctat cgct agaa attc agaa agga ...

The discovery of the structure of DNA

In 1943 american scientist Oswald Avery proved that DNA, and not proteins, as had been previously thought, carried the genetic information of a cell, resulting in several attempts to discover the structure of DNA. By the 1950s, a number of dicoveries about DNA had been made, but the full structure was yet to be found. Two main teams were working on it in England: Maurice Wilkins, and Rosalind Franklin were attempting to deduce the structure through X-ray spectroscopy at King's college London, while James Watson and Francis Crick were working on a more theoretical basis, by trying to work out what structures could have the necessary properties for DNA at Cambridge. While Watson and Crick took the credit for the structure of DNA, it is known that much of their work was based on X-ray data shown to them by Maurice Wilkins, and taken by Rosalind Franklin. The data showed the helical structure that is distinctive of DNA. Franklin's role in the discovery of DNA was crucial, and she never received much of the credit for it as she died shortly afterwards of cancer.

Structure of DNA

DNA is a polynucleotide ie. it is composed of many base units called nucleotides. Each DNA nucleotide is composed of a phosphate group, a deoxyribose sugar, and a nitrogenous base (one of thymine, guanine, adenine, and cytosine). The phosphate group and the deoxyribose sugar form an alternating chain, often called the sugar-phosphate backbone, of the DNA molecule, while the nitrogenous bases "stick out" to one side. In the double helix structure, hydrogen bonds form between thymine and adenine and cytosine and guanine, bonding the two chains together.






The Chemical Structure of DNA


    • Thymine: 2,4-dioxy-5-methyl pyrimidine
    • Cytosine: 2-oxy-4-amino pyrimidine


The Biological Functions of DNA




Mutations and Variations of DNA






  • Forensic Science:



  • Genetic Engineering:



Discovering DNA: History & Research




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