Biomolecules are polymers or macromolecules which take part in the metabolic activities of the living cell. Some common examples of Biomolecules are lipids, hormones, vitamins, proteins, nucleic acid and carbohydrates. Carbohydrates are polymeric forms of monosaccharide units which are bonded with glycosidic linkage to form oligosaccharide and polysaccharides like starch, cellulose etc.
Carbohydrates are a major source of energy for the living body. Proteins are formed by monomers, amino acids which are bonded with each other through peptide linkage. Proteins are mainly involved in structural units like nail, hair etc. Lipids are related to fatty tissues. Nucleic acids such as DNA and RNA are also polymeric forms like carbohydrates. Nucleic acids are composed of certain units such as phosphate group, nitrogenous base and deoxyribose or ribose sugar. These three units are bonded in a certain manner to form a long helical chain of DNA or RNA.
DNA is a double strand helical shaped molecule which is mainly related to transfer the genetic information from one generation to the next. On the contrary, RNA is a single strand molecule which involves in the protein synthesis. Do you know how DNA and RNA related with each other are? Is there any relation between these two forms of nucleic acid? Let’s discuss some common differences and functions of both of these nucleic acids.
Another important characteristics of nucleic acids is their ability to carry information from genes in the cell nucleus to certain structures in the cytoplasm that direct major biochemical processes.
For example, the building of proteins is controlled by the group of nucleic acids known in general as ribonucleic acid (RNA). The structures and functions of the three types of RNA molecules and the structure and function of DNA are shown below.
The main function of nucleic acid are listed below.
Nucleic acids are the genetic material for all living cells.
- It is involved in the storage and transfer of genetic material from one generation to the next.
The genetic material of all the cells in a living organism is the same and has all the information required for making an identical organism.
- Nucleic acids determine the phenotype of an organism.
- Other functions of nucleic acids include catalysis (enzyme like action eg: ribosomes) and co enzyme action (RNA acts as co enzyme for the enzyme telomerase).
Polysaccharides are composed of mono saccharides and proteins are composed of amino acids, nucleic acids are composed of long chains of repeating units called nucleotides. DNA molecules are the largest of the naturally occurring organic molecules.
Each nucleotide in a chain is made up of three components.
- Nitrogen containing hetero cyclic base
- Phosphoric acid unit
The sugar is a pentose either ribose or de-oxyribose. The only difference between these two sugars is at carbon number 2, where ribose has a hydrogen atom and an -OH group and deoxyribose has two hydrogen atoms. As the name indicates the sugar in DNA is deoxyribose and that in RNA is ribose.
- The first two of the five different bases found in nucleic acids are adenine and guanine which contains double ring bases and are classified as purines.
- The other three are cytosine, thymine and uracil which are single ring bases and belong to the class of compounds called pyrimidines.
Purines and pyrimidines are bases because the nitrogen atom present can accept the proton.
The pentose forms an ester bond with a phosphoric acid unit through the -OH on carbon 5 and forms another bond with the base through the -OH group on carbon 1. Water is eliminated as the bonds are formed.
When successive nucleotides bond to form long-chain nucleic acids, the phosphoric acid units form a second ester bond through the -OH group on carbon 3 of the pentose unit of another nucleotide. The alternating sugar-phosphoric acid units form the backbone of the nucleic acids.
The sequence of the four bases in a nucleic acid, like the sequence of amino acids in proteins, is its primary structure. Like proteins, nucleic acid also have a secondary structure.
A DNA molecule has two polynucleotides chains wound around one another to form a double helix, a structure which can be compared with a spiral staircase.
If one chain of the helix has a G base it must always be bonded to C base on the other chain, and an A base must always be bonded to T base. This arrangements gives "Steps" of almost equal lengths and explains why amounts of C and G and amounts of A and T in DNA molecules are always equal.