DNA Structure and Discoveries

Two strands of DNA are connected by hydrogen bonds, forming a double-helix structure. These bonds are crucial for maintaining the stability of the molecule.

Nitrogenous bases are found on the inside of the DNA molecule, forming the 'rungs' of the ladder. These bases contain nitrogen and are responsible for storing and transmitting genetic information.

Adenine always pairs with Thymine (A-T), and Guanine always pairs with Cytosine (G-C) due to their specific shapes and potential for hydrogen bonding. This complementary base pairing is vital for DNA replication and transcription.

The two strands of DNA run in opposite directions (5' to 3' and 3' to 5'). The direction is determined by the number of carbons on the sugar molecule.

The consistent pattern of DNA base pairing (A-T, G-C) ensures accurate DNA replication and contributes to the unity of life. However, variations in the sequence of these bases are the source of genetic diversity among living organisms.

Erwin Schrodinger, a theoretical physicist, wrote a book called "What is Life?" in 1944. This book explored the ideas of information storage and transmission within living organisms, emphasizing the role of chromosomes in carrying this information, and suggesting that this information was encoded within the DNA molecule.

Chargaff's Rules, formulated in 1949, state that the amount of adenine (A) in DNA is always equal to the amount of thymine (T), and the amount of guanine (G) is always equal to the amount of cytosine (C). This means that purines (A and G) pair with pyrimidines (T and C), and the ratio of A:G can vary between different species.

Linus Pauling, a renowned scientist, discovered the α-helix secondary structure of proteins in 1951. This discovery fueled his research into the structure of DNA, leading him to propose a triple helix model with a sugar-phosphate core. However, his model was ultimately incorrect.

James Watson and Francis Crick, along with Rosalind Franklin, made significant contributions to unraveling the structure of DNA in 1953. Using X-ray crystallography, Franklin and her colleague provided crucial data showing the sugar-phosphate backbone on the outside of the molecule and the antiparallel nature of the two DNA strands. Watson and Crick, using Franklin's data, built a 3D model of DNA and concluded it was a double helix, with base pairs forming the core.

The DNA molecule has a double helix structure. The outer part of the helix is composed of a sugar-phosphate backbone, where deoxyribose sugar molecules are linked by phosphodiester bonds. The inside of the helix is made up of nitrogenous bases (adenine, thymine, guanine, and cytosine) held together by hydrogen bonds.

Complementary base pairing is a fundamental principle of DNA structure. Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C), forming two hydrogen bonds between A and T, and three hydrogen bonds between G and C.

The two strands of DNA run in opposite directions, meaning that one strand runs from 5' to 3', while the other runs from 3' to 5'. This antiparallel arrangement is crucial for DNA replication and other processes.

The outer edge of DNA bases is exposed and available for interaction with proteins. This accessibility plays a vital role in gene expression and DNA replication, allowing proteins to recognize and bind to specific sequences.

The sugar-phosphate backbone of DNA is negatively charged due to the presence of phosphate groups. This negative charge is important for DNA interactions with proteins and other molecules.

The discovery of DNA's double helix structure was a monumental achievement in biology. It provided the key to understanding how genetic information is stored and transmitted, paving the way for countless advancements in genetics and medicine.