Molecular Biology

Introduction

The term molecular biology was given by William Astbury in 1945. Development in this sector was very late due to the lack of advanced technology as we have now. The study of molecular biology in the cells of primitive organisms such as bacteria and bacteriophages provided more clear-cut information about molecular cell reactions than animal cells. The discovery of the DNA double helix model by Watson and Crick in 1953 based on research done by Franklin and Wilkins, changed the whole scenario of the research sector, therefore paving the way towards molecular biology of the cell. The central dogma of transformation of DNA to RNA and in turn into protein is of prime importance. It’s not only the study of molecular types and mechanisms but it also includes tools and techniques like PCR being the notable one. It also plays a critical role in understanding cell functions, internal processes that help to create new discoveries further.

History of Molecular Biology 

History of molecular biology is very extensive but few discoveries that impacted much on the development of molecular biology are worth discussing. 

• The Frederick Griffith experiment: – observed transformation of one bacterium into another, but could not explain the reason. Later on in 1944 Avery, Macleod, McCarty explained the transformation
• Hershey and Chase experiment: – A strict competition arose whether DNA or PROTEIN was the genetic material which later on was cleared beautifully by Hershey and Chase. They used E.coli cells as host and bacteriophage as prop and used radioactive tagging to differentiate the transfer of protein or DNA (as we know now). DNA had radioactive phosphorus whereas Protein had radioactive Sulphur and on mixing the two cells, it was observed that E.coli cells had radioactive phosphorus which proved that genetic material that passed was DNA

Basic Structure and Features

Basic composition of DNA was known to contain 4 bases – Adenine, Guanine, Cytosine and Thymine. Amount of these 4 bases was given by Erwin Chargaff which stated that for any species, ratio of purines and pyrimidines must be 1:1 (A+G= T+C). Later-on the double helix model was discovered using X-Ray Crystallography. 

Molecular biology is incomplete if we neglect the basic elements of the topic. They are: –

• Nucleosides: – pentose sugar and N-Bases form nucleosides
• Nucleotides: – nucleosides plus the Phosphate linkage forms nucleotides
• Gene: – specific sequences of nucleotides that encodes for a protein
• DNA-double helical model: – Anti-parallel, with its 5’ end joined to 3’ end of its complementary strand where sugar and phosphate forms the backbone of the strand and bases project inside. Adenine is paired to Thymine via 2 H-Bonds and Cytosine is paired to Guanine via 3 H- Bonds. The two chains are coiled in a right-handed manner with pitch= 3.4nm.and the plane of one base pair stack over the other and H-Bonds together give extra stability

Central Dogma

Central dogma was given to Crick which stated that DNA is transformed into RNA (via transcription), then to protein (via translation). Retro viruses have a reverse transcription mechanism also. 

Replication of DNA: – Semi-conservative mode (half parental -half new), proved by Meselson and Stahl. Here the DNA replicates and forms its own copy at the time of cell division. 

Transcription of DNA into RNA: – DNA acts as a template and forms m-RNA which contains the code for the protein to be formed. This m-RNA is in inactive form but made active by splicing where the introns, the non-functional parts are removed and RNA is made ready to translate for protein.

Translation: – m-RNA is then attached to ribosomes and along with t-RNA the entire process of translating genetic code to protein is done. This requires a no. of factors and complexes.

Tools and techniques in molecular biology: – The most important ones are: – 

1. PCR: – It stands for Polymerase Chain Reaction, is a versatile technique to amplify a DNA molecule to billions of copies. It has many applications as in studying gene expression, pathogen detection and mutation detections.
2. Gel Electrophoresis: – a technique used to separate strands of DNA as per their sizes on a polyacrylamide gel.

Some Important Definitions

• Genome: – A complete set of chromosomes in a cell is called a genome
• Genetics: – branch of science especially molecular biology that deals with inheritance of characters from parents to off-springs
• DNA fingerprinting: – one of the most extensive out-come of molecular biology used to evaluate genetic differences between two individuals

Conclusion

Molecular biology is becoming a vast area of research and analysis with advancement of technology. The compositions of a cell and its constituents are elementary aspects of molecular biology. DNA is the genetic material with very vast applications in the functioning of cells such as replication, transcription, translation. Chromosomes are packed DNA molecules inside the nucleus which decides the organism’s diversity. The tools and techniques from the practical structure where the real implications of molecular biology are seen. With coming technology more new discoveries in this area will be unleashed.