Proteins

Proteins Most structurally and functionally diverse group: Structural material Enzymes Transport molecules Cell communication Defense movement General structure of an amino acid (building block)

Proteins There are 20 different R-groups in living organisms and therefore 20 different amino acids See page 42-43 for the various R group structures

Proteins Amino acids join together to form polypeptides through condensation reactions The bond is called a peptide bond:

Polypeptides can only be built in one direction They have an N-terminus (NH2) and a C-terminus (COOH) A series of amino acids is called a polypeptide chain

Proteins Of the 20 amino acids, 8 are considered to be essential because humans cannot produce them; they must be consumed The word protein suggests that a polypeptide chain has gone through several degrees of structural changes to become a final product There are 4 structural levels in the creation of a protein

Proteins Primary (1º) Structure The order of amino acids in a chain The sequence of amino acids is determined by the genes that “coded” for it Structure determines function! Consider sickle cell anemia

Sickle cell anemia results from one single amino acid substitution at the 6 position (6th AA)

Proteins Secondary (2º) structure The H-bonds among the amino acids form alpha- helices or beta-pleated sheets

Proteins Tertiary (3°) Structure Interactions between distant amino acids create “whole molecule” folding Hydrophobic Interactions: cytoplasm is water-based, so hydrophobic amino acids cluster away from water H-bonds and ionic bonds may form Disulfide bridges form between sulfur groups. These interactions anchor the 3D shape of the protein

Proteins

Proteins Quaternary (4°) structure: Clustering of two or more tertiary polypeptides through hydrophobic interactions Polypeptides then become a functional protein

Proteins Protein denaturation: the unfolding and destruction of protein functionality Causes: pH, salinity, temperature These can disrupt disulfide bonds, H-bonds, and ionic bonds The 3D shape is altered Some proteins can return to their functional shape after, but some cannot

Proteins Try these: P.50 #19, 20, 22, 23, 24, 25,