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Nucleic Acids


Table of Content

Define of Nucleic Acid

Nucleic acids are large, organic molecules present in living cells. DNA and RNA are nucleic acids. They are the polymers of nucleotides. There are three chemically distinct components in a nucleotide. These are as follows- Phosphate group, sugar known as Deoxyribose or Ribose and nitrogenous bases. There are two types of nitrogenous bases - Purines and Pyrimidines.  Purines includes adenine and guanine whereas pyrimidines include thymine and cytosine. DNA contain all 4 bases, that is, adenine, guanine, thymine and cytosine. But in RNA, thymine is replaced by uracil.

Nitrogenous bases

Fig. 1. Nitrogenous bases

DNA contain deoxyribose sugar whereas RNA contains ribose sugar

Structure deoxyribose and ribose sugar

Fig. 2. Structure Deoxyribose and Ribose Sugar

Structure of the DNA

DNA is a double helix formed by twisting of two polynucleotide chains around each other.  Watson and Crick proposed the DNA structure using X-ray diffraction studies. The two strands are antiparallel to each other. The bases are stacked inside the helix. The two helices are bonded together via hydrogen bond. Adenine forms two hydrogen bonds with thymine and cytosine forms three hydrogen bonds with guanine.

Hydrogen Bonding in DNA

Fig. 3. Hydrogen Bonding in DNA

DNA is negatively charged due to the presence of phosphate groups. This negative charge is stabilized by basic proteins known as histone proteins.

Structure of the RNA 

RNA exists as single stranded structure. In RNA, thymine is replaced by uracil. There are 3 major classes of RNA found:

  • Messenger RNA is a sequence of nucleotides that codes for proteins. In messenger RNA, nucleotides are arranged in the form of codons.

  • Transfer RNA is used during protein synthesis. It is found in the cytoplasm.

  • Ribosomal RNA is also found in cytoplasm and is the most abundant RNA found in cells.

Denaturation of DNA

DNA exists in double stranded form. When two DNA strands separate from each other, DNA is said to be denatured. Heating or alkaline pH denatures the DNA. The temperature at which DNA double strands can be separated is known as Melting Temperature. Breakage of G-C base pairs needs high temperature as compared to breakage of A-T base pairs due to triple bond in G-C base pairs. But if denaturing agents are removed, the DNA will regain its structure and it is said to be renatured.

Boiled eggs become hard because egg proteins and DNA gets denatured. A classic example of denaturing in proteins comes from egg whites, which are typically largely egg albumins in water. Fresh from the eggs, egg whites are transparent and liquid. Cooking the thermally unstable whites turns them opaque, forming an interconnected solid mass.

Quantification of DNA content is performed using Absorption at 260nm.

Importance of Nucleic Acids/Functions of Nucleic Acids

Deoxyribonucleic acids and ribonucleic acids are the key components which control almost all the metabolic activities in an organism

  • DNA is necessary for transferring genes from parents to offspring.

  • DNA stores all the information of a cell.

  • Loss of DNA content is associated with lots of diseases.

  • DNA samples are used to identify the suspect or father of an unidentified child.

  • DNA sequence helps in studying relationship between the two organisms such as which organism originates from which ancestor.

  • Without DNA, no protein synthesis will occur.

  • RNA is essential for protein synthesis.

RNA and DNA helps to understand the diseases and to find the cure of genetic diseases.

You can also refer to  

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Nucleic Acids

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