DNA (Deoxyribonucleic Acid) Chapter-3

 History of Genomic DNA Discovery

The discovery of genomic DNA and its structure is a tale of scientific progress spanning over a century. Here are the key milestones:

Early Discoveries

1. Friedrich Miescher (1869):
• Miescher, a Swiss physician and biologist, discovered a substance he called "nuclein" (now known as DNA) in the nuclei of white blood cells. He isolated it from pus cells and noted its high phosphorus content.
2. Albrecht Kossel (1881-1890s):
• Kossel identified the five nitrogenous bases that make up nucleic acids: adenine, cytosine, guanine, thymine, and uracil. His work helped in understanding the chemical nature of nucleic acids.

The Role of DNA in Heredity

3. Frederick Griffith (1928):
• Griffith discovered the "transforming principle" while working with Streptococcus pneumoniae bacteria. He found that a non-virulent strain could be transformed into a virulent one by a substance from the virulent strain, suggesting the presence of a genetic material that could be transferred.
  
  
  
4. Avery, MacLeod, and McCarty (1944):
• Building on Griffith's work, they demonstrated that DNA is the "transforming principle." They showed that purified DNA from virulent bacteria could transform non-virulent bacteria into a virulent form, indicating that DNA carried genetic information  

3. Hershey and Chase (1952):
• In their famous experiment using bacteriophages (viruses that infect bacteria), they provided strong evidence that DNA, not protein, is the genetic material. They used radioactive labeling to show that DNA entered bacterial cells during infection, whereas proteins did not.

Video: https://www.youtube.com/watch?v=ZtSfFqqhEIY 

Discovery of the DNA Structure

6. Erwin Chargaff (1950):
• Chargaff discovered that the amount of adenine (A) equals thymine (T) and the amount of cytosine (C) equals guanine (G) in any given DNA molecule. This became known as Chargaff's rules, which were critical for understanding the base pairing in DNA.
7. Rosalind Franklin and Maurice Wilkins (1951-1953):
• Franklin's work with X-ray diffraction provided key insights into the helical structure of DNA. Her famous Photo 51 showed the characteristic X-shaped pattern of a helical structure.
8. James Watson and Francis Crick (1953):
• Using Franklin's data, along with other research, Watson and Crick proposed the double helix model of DNA. They suggested that DNA is composed of two strands that form a helical structure, with the bases pairing specifically (A with T, and C with G) in the center. Their model explained how DNA could be replicated and carry genetic information.

Post-Discovery Developments

9. Meselson and Stahl (1958):
• Their experiment confirmed the semi-conservative replication of DNA, showing that each strand of the original DNA molecule serves as a template for a new strand.
10. Human Genome Project (1990-2003):
• An international research effort aimed at sequencing the entire human genome. Completed in 2003, it identified the sequence of approximately 3 billion base pairs and mapped all the genes of the human genome. This project has had profound implications for biology, medicine, and genetics.
11. CRISPR-Cas9 (2012):
• The development of CRISPR-Cas9 as a genome editing tool by Jennifer Doudna, Emmanuelle Charpentier, and their colleagues revolutionized genetic research. It allows for precise modifications to DNA, opening new avenues for genetic engineering and gene therapy.

 

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