Because of the seeming simplicity of DNA’s chemistry, biologists in the 1940s had difficulties embracing it as the genetic material. DNA was once thought to be a lengthy polymer made up of only four chemically similar components. DNA was originally studied using x-ray diffraction analysis, a technique for determining a molecule’s three-dimensional atomic structure, in the early 1950s. DNA was discovered to be made up of two strands of polymer coiled into a helix based on early x-ray diffraction measurements. The discovery that DNA was double-stranded was essential, as it was one of the key clues that led to the Watson-Crick structure of DNA. The potential of DNA for replication and information encoding became apparent only after this paradigm was proposed.
DNA Structure
The DNA molecule’s structure resembles a twisted ladder. This structure is described as a double-helix. It’s a nucleic acid, and nucleotides make up all nucleic acids. Nucleotides are the building blocks of DNA, and each nucleotide is made up of three separate components: sugar, phosphate groups, and nitrogen bases.
The basic building elements of DNA are nucleotides, which contain a sugar group, phosphate group, and nitrogen base. Sugar and phosphate groups join nucleotides together to make each strand of DNA. Nitrogen bases include adenine (A), thymine (T), guanine (G), and cytosine (C).
The four nitrogenous bases are paired as follows: A with T, C with G, and D with E. The double helix structure of DNA, which resembles a twisted ladder, requires these base pairs to function. The genetic code, often known as DNA instructions, is determined by the arrangement of nitrogenous bases.
Sugar is the backbone of the DNA molecule and is one of the three components that make up its structure. Deoxyribose is another name for it. The opposing strands’ nitrogenous bases establish hydrogen bonds, resulting in a ladder-like structure.
Adenine (A), thymine (T), cytosine (C), and guanine (G) are the four nitrogen bases that make up the DNA molecule. Purines are A and G, whereas pyrimidines are C and T.
DNA strands flow in opposite directions. The hydrogen connection between the two complementary bases holds these strands together. The strands are helically twisted, with each strand forming a right-handed coil and a single turn containing ten nucleotides.
Each helix has a 3.4-nm pitch. As a result, the distance between two adjacent base pairs is 0.34 nm.
Types of DNA
There are four major types of double-stranded DNA. The interaction of complementary base pairs connects them.
B-form DNA– This is the most common type of DNA, in which two strands of DNA are coiled around the same axis, each in a right-hand helix. The two strands are held together by H-bonding between the bases.
A-form DNA – It is similar to B-form DNA in that it is a right-handed double-helical structure with a thicker structure and a shorter space between base pairs. When DNA is dehydrated, it converts to the A form to protect it from harsh circumstances like desiccation. When protein binding removes the solvent from DNA, it can also form.
C-form DNA – When DNA is exposed to low humidity and certain ions such as Li+ and Mg2+, it takes the form C-form DNA. This is an unstable form that doesn’t exist in nature. The nucleotide conformations in B and C-DNA are similar, but the ratios are different.
Z-form DNA- It has a left-handed helical helix, making it the third type of duplex DNA. In Z-form DNA, a zigzag structure is created by alternating purines and pyrimidines. It’s thought to play a role in gene regulation and transcription because it’s found at the start of a gene.
Properties of DNA
- Right-handed or left-handed DNA helices exist. However, the right-handed helices of the B – conformation of DNA are the most stable.
- When two strands of DNA are heated, they separate and then re-hybridize when they are cooled.
- Melting temperature is defined as the temperature at which the two strands separate completely (Tm). For each sequence, the melting temperature is different.
- Because the C-G pair has three hydrogen bonds, the B sample of DNA with a higher melting point must have more C-G.
- Every protein in all species has a sequence of amino acids that is encoded by the base sequence along the DNA molecule.
CONCLUSION
Although the chemical DNA was discovered in 1869, it was not until 1943 that its significance in genetic heredity was established. James Watson and Francis Crick discovered that DNA is a double-helix polymer, a spiral composed of two DNA strands twisted around each other, in 1953, with the help of biophysicists Rosalind Franklin and Maurice Wilkins. Scientists’ understanding of DNA replication and hereditary regulation of cellular activity has improved dramatically as a result of the breakthrough.
A lengthy chain of monomer nucleotides makes up each strand of DNA. DNA nucleotides are made up of a deoxyribose sugar molecule with a phosphate group attached and one of four nitrogenous bases: adenine, guanine, and pyrimidine (cytosine and thymine). The phosphate of one nucleotide and the sugar of the next establish covalent connections, generating a phosphate-sugar backbone from which the nitrogenous bases protrude. Hydrogen bonds between the bases hold one strand to the other; the sequence of these bonds is specific—adenine links only with thymine, and cytosine bonds only with guanine.