Two helical strands that are wound around the same axis make up DNA. DNA helices are classified as either right-handed or left-handed depending on the direction they are wound. However, right-handed helices DNA is the most stable and benchmark structure. The two helical chains are in opposition to one another. As a result, one strand extends from 5′ to 3′ and the other from 3′ to 5′. The strands are made of four types of nitrogenous bases (A, T, C, and G). These nitrogenous bases serve as genetic information stores and, as a result, encode the amino acids that form proteins.
Physical and Chemical Properties of DNA
Solubility
DNA is polar in nature and thus soluble in water. Its highly charged phosphate-sugar backbone gives it its polarity. However, in the presence of salt and alcohol, it is insoluble.
Absorption
At 260 nanometers, the DNA bases can absorb ultraviolet light. A spectrophotometer can measure this absorption. The amount of ultraviolet light absorbed increases with the order of the bases. For example, at 260 nm, a single-stranded DNA absorbs 1.37 units, whereas a double-stranded DNA absorbs 1.00 unit at 260 nm.
Denaturation and Renaturation
On heating, both strands denature, and on cooling, they can renature. The melting temperature, which varies depending on the precise DNA sequence, is the temperature at which these strands are permanently separable.
In contrast to the region of higher concentration A-T, which is only bonded with two hydrogen bonds, the region of higher concentration of C-G has a higher melting temperature because these bases are bonded with three hydrogen bonds, which require more energy to break.
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