Proteins Structure and Funcitons

Functions and Structure of Proteins
Proteins Functions 
Proteins are huge biomolecules that sometimes have mainly a structural function. For example, in humans, ker­atin is a protein that makes up hair and nails, and collagen is a protein found in connective tissue, including cartilage, bone, and the fibrous connective tissue of ligaments and tendons. Muscles contain proteins that account for mus­cles' ability to contract.
Some proteins function as enzymes (en'z1mz), neces­sary contributors to the chemical workings of the cell and, therefore, of the body. Enzymes are organic catalysts that speed chemical reactions. The reaction occurs when the reactants are close to one another on the enzyme surface. Enzymes also catalyze reactions that break down reactants into their mo­lecular subunits. Enzymes work so quickly that a reaction that might normally take several hours or days without an enzyme takes only a fraction of a second when an enzyme is present.
Proteins Structure 
The unit molecules found in proteins are called amino acids (ah-me'no as'idz). The name amino acid refers to the fact that the molecule has two functional groups: an amino group and an acid group.
Amino acids differ from one another by their R groups, the remainder of the molecule. In amino acids, R groups vary from a single hydrogen atom (-H) to a complicated ring. Because about 20 different common amino acids are found in the proteins of living things, there are also about 20 different types of R groups.
A peptide bond (pep'tid bond) joins two amino acids together.
(sin'the-sis) the acid group of one amino acid reacts with the amino group of another amino acid, and water is given off. A dipeptide contains only two amino acids, but a polypeptide can contain hundreds of amino acids. Polypep­tides have three levels of structure. The pri­mary structure is the sequence of amino acids in that particular polypeptide. The secondary structure is often a helix, held in place by hydrogen bonding. The tertiary structure is the final three-dimensional shape of the polypeptide.
Some proteins have only one polypeptide chain, while others have more than one type of polypeptide chain, each with its own primary, secondary, and tertiary structures. These separate polypeptides are arranged to give some pro­teins a fourth level of structure, termed the quaternary structure. llemoglobin is a complex protein with a quaternary structure.
Proteins have both structural and enzymatic functions in the human body. Amino acids are the unit molecules for peptides and polvpentidea.

Posted in Human Anatomy and Physiology