PROTEINS

Learning Outcomes: B4 - describe the chemical structure of proteins List functions of proteins Draw and describe the structure of an amino acid Describe the formation of peptide bonds Describe the 4 levels of protein structure

ELEMENTS All contain C, H, O, N Some contain S

MONOMERS Amino Acids consist of an acid (carboxyl) group, an amino group, and a variable R group (R for “remainder”)

There are 20 amino acids, each with a unique R group some of these are known as “essential amino acids” because our bodies can’t synthesize them Examples: (see p. 37, note different R groups)

POLYMERS Proteins consist of chains of amino acids A single protein may contain several hundred amino acids

A dipeptide contains two amino acids joined by a peptide bond

Condenstation Synthesis A molecule of H 2 O is removed to form a peptide bond between two amino acids

Hydrolysis Proteins can be broken down into amino acids A molecule of H 2 O is added when a peptide bond is broken

A polypeptide is a chain of many amino acids joined by peptide bonds

LEVELS OF STRUCTURE Proteins have four levels of structure, resulting in large complex molecules with definite 3D shapes

Primary structure The sequence of amino acids in the polypeptide chain

Secondary structure The chain forms a shape such as a helix (coil) or pleated sheet Held together by hydrogen bonds between R groups Amino acid basics

Tertiary structure The coil or sheet folds into a 3-dimensional shape - may be due to hydrogen, ionic or covalent bonding Hydrophobic parts on the inside, hydrophilic parts on the outside

Quaternary structure Two or more polypetide chains combine to form a complex molecule Ex. Hemoglobin contains 4 polypeptide chains

The 3 dimensional shape of a protein is important to its function

FUNCTIONS 1. Structural proteins in all parts of the body Ex. Keratin in hair and nails; collagen in skin; actin and myosin in muscle

Muscle proteins form long fibers

2. Blood proteins such as hemoglobin, clotting proteins, antibodies

Hemoglobin is the oxygen carrying protein in red blood cells consists of four polypeptide chains and an iron- containing heme group

3. Enzymes - very important! Enzymes catalyze chemical reactions in all parts of the body (we have over 2000 different ones) All enzymes are proteins The specific shape of the enzyme molecule allows it to bind to reactants

4. Cell membranes proteins are found in cell membranes, where they have various functions (along with phospholipids - more on this later!)