Proteins are the most complex biological molecules. They are made up of C,H,O,N, and a little S (carbon, hydrogen, oxygen, nitrogen, and a little sulfur). They accomplish all life functions. Proteins are polymers of amino acid monomers. Amino Acids are joined by peptide bonds. A peptide bond is when the carbon in the carboxyl group of one amino acid connects to a nitrogen in the amino group of another amino acid. This happens through dehydration synthesis, a process when a molecule loses water. Once all the amino acids join together or connect by peptides bonds, they form a sequence of amino acids also known as a polypeptide chain that become the primary structure of a protein.
Once one or more polypeptide chains twist into a 3-D shape to form a protein. Hydrogen bonding helps aid the atoms in a protein hold together and and giving it its shape. Hydrogen bonding is the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. This is called the secondary structure. .
After the secondary structure the tertiary structure is formed. The tertiary structure is the last geometric shape that a protein takes. This shape is determined by the interactions between the R-group or side chains on the amino acids. These interactions are called disulfiede bridges. Disulfiede bridges are made by disulfide bonds. Disulfiede bonds are covalent bonds that usually come from the coupling of two think groups. The disulfide bridge is formed when the sulfur atom from one cysteine forms a single covalent bond with a sulfur atom from a second cysteine in a different part of the protein. .
Proteins are responsible for all life activities in a cell. This means they are responsible for muscle contraction. Muscles are made up of two major protein filaments. A thick filament composed of myosin and a thin filament composed of actin. Muscle contractions occur when these two filaments slide over one another in a series of reptitive events.