THE BASIC STRUCTURE and FUNCTION of DNA and RNA:

DNA vs. RNA STRUCTURE

Deoxyribonucleic acid ( DNA ) and Ribonucleic acid ( RNA ) enable the cells of living organisms to manufacture proteins. Proteins can exist as singular or multi-strand molecular units with very complex functions; they can be used to form structural cell wall components, neurotransmitters, enzymes, and other structures necessary for an organism’s survival. The interactions between DNA and RNA molecules are very complex, but generally speaking, their functions within a cell differ in the following manner: DNA encodes biological information, and RNA transfers biological information. Additionally, DNA consists of a double-stranded helix, while RNA exists as a single-stranded molecule of which there are three types: Messenger RNA ( mRNA ), transfer RNA ( tRNA ), ribosomal RNA ( rRNA ).

How does DNA encode biological information? DNA can be thought of as a type of “ alphabet “ that consists of four heterocyclic nitrogenous bases that act as the “ letters “ used to assemble mRNA molecules. The base pairs of DNA are adenine ( A ), thymine ( T ), guanine ( G ), and cytosine ( C ). The adenine bases on one strand of DNA bind to thymine bases located on a complementary strand of DNA. Likewise, guanine bases pair with cytosine bases within double-stranded DNA molecules.

Differing sequences of A, T, G, and C create regions of DNA known as “ genes “. When a helicase enzyme unwinds a double-stranded DNA molecule, gene sequences on one ( or both ) of the DNA helices can be “ read “ by enzymes that construct mRNA molecules. mRNA molecules then transfer information to sequences of tRNA molecules within cell structures called “ ribosomes. “ Unlike DNA, RNA base pairs consist of adenine ( A ), thymine ( T ), guanine ( G ), and uracil ( U ). The uracil in mRNA molecules binds with cytosine found in DNA strands.

Within ribosomes, mRNA, tRNA, and rRNA engage in complex reactions that arrange sequences of amino acids into proteins. Since mRNA sequences are constructed according to the gene template upon which they are synthesized, the sequence of amino acids synthesized by ribosomes is directly dependent upon which genes are actively expressed within a cell.