Proteins

Proteins (are large biomoluelcule , or marcomoleucue , consisting of one or more long chains of amino acids  resiudes . Proteins perform a vast array of functions within organisms , including

catalayzing metablic reaction  , responding to stimulas , and transporting molecule  from one location to another. 

A linear chain of amino acid residues is called a polypetide . A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides .

 individual amino acid residues are bonded together by peptide bonds  and adjacent amino acid residues. 

Structure of protein  

Primary structure : the amino acids sequence 

.

Secondoary structure : regularly repeating local structures stabilized by hydrogen bonds . The most common examples are the a helix ,beta helix and turns . Because secondary structures are local, many regions of different secondary structure can be 

present in the same protein molecule.

Tetirary structure : the overall shape of a single protein molecule or  the spatial relationship of the secondary structures to one another. Tertiary structure is generally stabilized by nonlocal interactions, most commonly the formation of a hydrophobic core , but also through salt brigdhe  hydrogen bonds, disulfide bonds , and even posttranslation modification ,  The term "tertiary structure" is often used as synonymous with the term fold. The tertiary structure is what controls the basic 

function of the protein.

Quandary structure  the structure formed by several protein molecules (polypeptide chains), usually called protein subunits