Sunday, February 15, 2009

A mutation is any permanant change in the DNA sequence. Most mutations are recognised because the phenotype, that is the characteristics displayed by an organism, have changed. There are different types of mutation. Mutations are rare events occurring at a rate of 1 in every 50 million bases added to the nucleotide chain. The rate of Mutation is 1 in10x7 cells to 1 in 10x12 cells. Most of the changes that happen are quickly repaired by our very efficient and accurate DNA repair system. But this repair mechanism is not foolproof. Failure to repair all mutations has led to the introduction of some mutations that have made organisms fitter and better able to adapt to their environments. However, many mutations have detrimental effects for an organism and it is these mutations that are the basis of many human genetic disorders and disease.
Please Click on the link below and Right Click and "Save"
Right Click and "Save" For FRANCOIS JACOB's Genetics of the bacterial cell NobelLecture,Decemberll, 1965

Sunday, January 4, 2009


Transcription transfers the genetic instructions from the DNA template to RNA and is the first step in expression of the genome . This highly regulated process consists of the synthesis of an RNA molecule by an RNA polymerase (RNA pol) that reads the template (or noncoding) strand of the DNA; the primary transcript will therefore carry the same genetic message as the other DNA strand, namely the coding strand.

Translation is the synthesis of a protein according to the genetic information. It is the second step of gene expression, following transcription, and is a universal and essential step for life. The process is called translation because it converts the genetic information of nucleic acid sequences, composed of four distinct nucleotides, to the polypeptide sequence composed of 20 distinct amino acids. An enzyme called aminoacyl-tRNA synthetase adds the correct amino acid to its tRNA. Amino acids are joined together in proteins by peptide bonds. This is carried out by the enzyme peptidyl synthetase. An initiation complex for translation forms by the assembly of the ribosomal subunits and initiator tRNA (met-tRNA) at the start codon on the mRNA. Several ribosomes can translate an mRNA at the same time, forming what is called a POLYSOME.


In a prokaryotic cell, transcription and translation are coupled; that is, translation begins while the mRNA is still being synthesized. In a eukaryotic cell, transcription occurs in the nucleus, and translation occurs in the cytoplasm.

Please Click on the link

Right click and "Save" for a paper on
Why is transcription coupled to translation in bacteria?

Tuesday, December 16, 2008


DNA replication, the basis for biological inheritance, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand. Hence, following DNA replication, two identical DNA molecules have been produced from a single double-stranded DNA molecule. Cellular proofreading and error-checking mechanisms ensure near perfect fidelity for DNA replication. In a cell, DNA replication begins at specific locations in the genome, called "origins". Unwinding of DNA at the origin, and synthesis of new strands, forms a replication fork. In addition to DNA polymerase, the enzyme that synthesizes the new DNA by adding nucleotides matched to the template strand, a number of other proteins are associated with the fork and assist in the initiation and continuation of DNA synthesis.

Download a PDF file (To save Right Click and "Save")
On "Roles of Nuclear Structure in DNA Replication"

For Notes on Bacterial Replication: (Right Click and "Save")

Click below to see an animation on DNA replication and also make a point to see the quiz in it:

Click for a You Tube Video:

Notes on "An expanded view of bacterial DNA replication" (Right Click and "Save Taget As")

Notes on "A Boradening View of Recombinational DNA Repair in Bacteria" (Right Click and "Save ")

Notes on "VIRAL DNA POLYMERASES" (Right Click and "Save ")

Details about "EUKARYOTIC DNA POLYMERASES" (Right Click and "Save")



Tuesday, November 25, 2008


In 1951, the then 23-year old biologist James Watson traveled from the United States to work with Francis Crick, an English physicist at the University of Cambridge. Crick was already using the process of X-ray crystallography to study the structure of protein molecules. Together, Watson and Crick used X-ray crystallography data, produced by Rosalind Franklin and Maurice Wilkins at King's College in London, to decipher DNA's structure. This is what they already knew from the work of many scientists, about the DNA molecule:
DNA is made up of subunits which scientists called nucleotides.
Each nucleotide is made up of a sugar, a phosphate and a base.
There are 4 different bases in a DNA molecule:
adenine (a purine)
cytosine (a pyrimidine)
guanine (a purine)
thymine (a pyrimidine)
By rule the number of purine bases equals the number of pyrimidine bases, which is known as Chargaff's Rule.
The number of A equals to T & G equals to C
The basic structure of the DNA molecule is helical and supercoiled, with the bases being stacked on top of each other. DNA can adopt a more compact configuration due to supercoiling. The degree of supercoiling in the cell is carefully controlled by the action of topoisomerases.



DNA structure: Revisiting the Watson–Crick double helix by Manju Bansal

To go into the cell and have a virtual tour of it showing the DNA molecule click below

Click here to build your own DNA molecule:

And if you want to extract a DNA online visit this virtual Lab:

To extract DNA from almost anything in your Lab: