Introduction to DNA, RNA and Proteins

Introduction to DNA, RNA and proteins

DNA

DNA is the basic hereditary material in all cells and contains all the information necessary to make proteins.
DNA is a linear polymer that is made up of nucleotide units. The nucleotide unit consists of a base, a deoxyribose sugar, and a phosphate. There are four types of bases: adenine (A), thymine (T), guanine (G), and cytosine (C). Each base is connected to a sugar via a ß glycosyl linkage. The nucleotide units are connected via the O3' and O5' atoms forming phosphodiester linkages.
In normal DNA, the bases form pairs: A to T and G to C. This is called complementarity. A duplex of DNA is formed by two complementary chains that are arranged in an anti-parallel manner.

RNA

RNA is a polymer that contains ribose rather than deoxyribose sugars. The normal base composition is made up of guanine, adenine, cytosine, and uracil.
When a cell receives a signal saying that a certain protein is needed, the code for producing protein is made. The DNA double helix unwinds and one strand of the helix becomes a template for producing the protein coding template. This template is a single strand of opposite bases (from DNA) and is called RNA (Ribonucleic Acid). Bases that are floating in the cell join up with opposite bases with Uracil taking the place of Thymine. This template is called mRNA (messenger RNA), because it serves as a code messenger between DNA and protein. The process of creating a mRNA from DNA is called transcription.

Proteins

A protein is a long train of amino acids linked together. Proteins have different functions;
they can provide structure (ligaments, fingernails, hair), help in digestion (stomach enzymes), aid in movement (muscles), and play a part in our ability to see (the lens of our eyes is pure crytalline protein) .
There are twenty amino acids that are commonly found in proteins. Each amino acid has a similar, yet unique structure.

Each amino acid has a different side chain (or R group). The side chains vary greatly in their complexity and properties. The side chain of glycine is simply a hydrogen. The side chain of tryptophan is based on the aromatic, bicyclic indole group. Amino acids are classified by the chemical nature of their side chains. One useful classification of the amino acids divides them into two groups, the polar (or hydrophilic) amino acids have side chains that interact with water, while those of the nonpolar (or hydrophobic) amino acids do not.

Each amino acid has its own specific code, made up of three bases called a codon. This is what the RNA sequence is made of. The mRNA then travels into the cytoplasm of the cells where proteins are then synthesized. tRNA
(transfer RNA) brings amino acids to the mRNA. The tRNA has a loop called the anticodon, which has the opposite sequence of letters than the mRNA, which hooks up to the mRNA at its complementary spot. Each of these tRNA can pick up a certain amino acid according to its sequence of bases. When one tRNA after another connects to the mRNA, a hydrogen bond is formed between the amino acids, forming a protein.

Protein structure

Protein structure is broken down into four levels:

Primary structure refers to the "linear" sequence of amino acids.
Secondary structure is "local" ordered structure brought about via hydrogen bonding mainly within the peptide backbone. The most common secondary structure elements in proteins are the alpha (a) helix and the beta (b) sheet (sometime called b pleated sheet).
Tertiary structure is the "global" three dimensional folding of a single polypeptide chain.
Quartenary structure involves the association of two or more polypeptide chain into a multi-subunit structure.