Proteins Proteins Proteins are major structuralmetabolic components in

Proteins

Proteins • Proteins are major structural/metabolic components in living things • Made of C, H, O, N, P, S • Building block: Amino Acids • Twenty different amino acids are used to build proteins in organisms. – A protein structure is complex

Figure 5. 15 -a Enzymatic proteins Defensive proteins Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. Function: Protection against disease Example: Antibodies inactivate and help destroy viruses and bacteria. Antibodies Enzyme Virus Bacterium Storage proteins Transport proteins Function: Storage of amino acids Function: Transport of substances Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes. Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. Transport protein Ovalbumin Amino acids for embryo Cell membrane

Figure 5. 15 -b Hormonal proteins Receptor proteins Function: Coordination of an organism’s activities Example: Insulin, a hormone secreted by the pancreas, causes other tissues to take up glucose, thus regulating blood sugar concentration Function: Response of cell to chemical stimuli Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells. High blood sugar Insulin secreted Normal blood sugar Receptor protein Signaling molecules Contractile and motor proteins Structural proteins Function: Movement Examples: Motor proteins are responsible for the undulations of cilia and flagella. Actin and myosin proteins are responsible for the contraction of muscles. Function: Support Examples: Keratin is the protein of hair, horns, feathers, and other skin appendages. Insects and spiders use silk fibers to make their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective tissues. Actin Myosin Collagen Muscle tissue 100 m Connective tissue 60 m

Amino Acids • All amino acids have the same base structure • Only one part is changed: Variable or “R” group

Polypeptides • Polypeptides are unbranched polymers built from the same set of 20 amino acids • A protein is a biologically functional molecule that consists of one or more polypeptides

Dehydration Synthesis • Amino acids are linked together by peptide bonds

• Proteins will differ in the number and order of amino acids • Primary structure: sequence of amino acids • Inherited from genetic information • Most important because this will determine the protein structure • STRUCTURE DETERMINES FUNCTION

Water-fearing amino acids § Hydrophobic u u “water fearing” amino acids try to get away from water in cell § the protein folds

Water-loving amino acids § Hydrophillic u u “water loving” amino acids try to stay in water in cell § the protein folds

• Secondary Structure • Results from hydrogens between repeating units • Can form: • Alpha helix • Beta pleated sheet

• Tertiary structure • Determined by the interactions among the various “R” groups

• Quaternary structure • Results when a protein consists of multiple polypeptide chains to form a macromolecule • Functional Protein

• If there is a change in the primary sequence then the protein will not fold correctly • This prevents the protein from working properly

Sickle celled Hemoglobin Normal Hemoglobin Primary Secondary and Tertiary Quaternary Function

What determines protein structure? • In addition to the primary structure, physical and chemical conditions can affect structure • Alterations in: • p. H • Salt concentration • Temperature • This is called DENATURATION

It’s SHAPE that matters! • Proteins do their jobs, because of their shape • Unfolding a protein destroys its shape • wrong shape = can’t do its job • unfolding proteins = “denature” • temperature • p. H (acidity) unfolded “denatured” In Biology, it’s not the size, it’s the SHAPE that matters! folded