Answer
Proteins are substances important for structural, metabolic, transport, and immunological functions in the body. Chemically,they are complexes of small molecules called amino acids which are made up primarily of carbon, hydrogen, nitrogen , oxygen ( and sometimes sulfur). The joining of amino acids( 20-21 ) to form human proteins involves four levels of organization-- primary, secondary, tertiary and quaternary. When two or more amino aids join together by dehydration synthesis, they form peptides( oligopeptides or polypeptides). This is the primary level of protein organization. The link between amino acids is the peptide bond( or amide), and the enzyme that catalyzes this endergonic reaction is peptidyl transferase. Some proteins are only one or two peptide chain(s) large.
Polypeptide chains often bend and coil to form helices and sheets that constitute the secondary level of organization. These coils and sheets of amino acids are stabilized mostly by hydrogen bonds. Research has shown that the nature of the secondary structure influences the subsequent type of folding of the protein molecule.
Tertiary structures refers to the three dimensional (3D) shape or conformation that a protein molecules assumes in space. Post secondary structure coiling or twisting of polypeptide chains may give rise to rigid rods, spheroid or globular molecules , These shapes are usually stabilized by side chain interactions and bonding involving the following bonds : disulfide bonds(S-S), hydrogen bonds, ionic bonds and hydrophobic bonds. In globular proteins the pimary linear backbone of the peptide chain may fold indifferent ways to but in fibrous proteins the primary linear chain tends to take the form of rod-like structures as in collagen and keratin. Quaternary structure involves the association or clustering of several polypeptide chains linked by different kinds of bonds to form large molecular aggregates. The beta pleat sheet is a form of quaternary organization of fibrous proteins. But this level of organization is more characteristic of globular proteins like hemoglobins.. Bonding at this level involves ionic bods, disulfide bonds, ionic bonds, hydrophilic and hydrophobic linkages.
Work Step by Step
The four levels of organization in the synthesis of proteins; primary, secondary, tertiary and quaternary
Primary level. The primary organization of a protein is the peptide or polypeptide chain composed of amino acids held by peptide bonds.
Secondary level. A peptide or polypeptide chain may coil, twist and turn upon itself to form helices, sheets and turns that are held in shape by hydrogen bonds that link side chains of the constituent amino acids, This is the secondary level of protein organization.
The tertiary level of organization also involves individual polypeptide chains. This is the three dimensional (3D) level where fibrous protein helices and pleats form long thin and rigid rods ( e.g. in collagen) while in globular proteins helices and sheets are short and become folded into compact spheroidal, flexible structures ( as in hemoglobins, albumins, insulin ).Bonds at this level include hydrogen bonds, disulfide bonds, ionic bonds, hydrophobic and hydrophilic bonds which link side chain components.
The quaternary level of organization involves two or more polypeptide chains ( dimers, trimers, tetramers---up to 60 or more monomers.) The quaternary configuration of the protein is the aggregate formed by the interactions of the polypetide chains together. Quternary aggregates are stabilized by the same kinds of bonding as in tertiary bonding --disulfide bonds, salt bridges, hydrophobic, hydrophilic and ionic bonds.
