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Transcript
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 H2O is removed to form a peptide bond between two amino acids Hydrolysis • Proteins can be broken down into amino acids • A molecule of H2O 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 ironcontaining 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!)