Proteins include a diversity of structures, resulting in a wide range of functions Protein functions include structural support, storage, transport, enzymes,
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Proteins include a diversity of structures, resulting in a wide range of functions
• Protein functions include structural support, storage, transport, enzymes, cellular communications, movement, and defense against foreign substances
Function: Selective acceleration of chemical reactionsExample: Digestive enzymes catalyze the hydrolysisof bonds in food molecules.
Function: Protection against diseaseExample: Antibodies inactivate and help destroyviruses and bacteria.
Function: Storage of amino acids Function: Transport of substances
Examples: Casein, the protein of milk, is the majorsource of amino acids for baby mammals. Plants havestorage proteins in their seeds. Ovalbumin is theprotein of egg white, used as an amino acid sourcefor the developing embryo.
Examples: Hemoglobin, the iron-containing protein ofvertebrate blood, transports oxygen from the lungs toother parts of the body. Other proteins transportmolecules across cell membranes.
Figure 5.15-b
Hormonal proteins
Function: Coordination of an organism’s activitiesExample: Insulin, a hormone secreted by thepancreas, causes other tissues to take up glucose,thus regulating blood sugar concentration
Highblood sugar
Normalblood sugar
Insulinsecreted
Signalingmolecules
Receptorprotein
Muscle tissue
Actin Myosin
100 m 60 m
Collagen
Connectivetissue
Receptor proteins
Function: Response of cell to chemical stimuliExample: Receptors built into the membrane of anerve cell detect signaling molecules released byother nerve cells.
Contractile and motor proteins
Function: MovementExamples: Motor proteins are responsible for theundulations of cilia and flagella. Actin and myosinproteins are responsible for the contraction ofmuscles.
Structural proteins
Function: SupportExamples: Keratin is the protein of hair, horns,feathers, and other skin appendages. Insects andspiders use silk fibers to make their cocoons and webs,respectively. Collagen and elastin proteins provide afibrous framework in animal connective tissues.
Polypeptides
• Polypeptides are un-branched polymers built from the same set of 20 amino acids
• A protein is a biologically functional molecule that consists of one or more polypeptides
• Amino acids are organic molecules with carboxyl and amino groups which are monomers of proteins
• Amino acids differ in their properties due to differing side chains, called R groups
• The primary structure of a protein is its unique sequence of amino acids determined by inheritance.
• Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain caused by H-bonds between polypeptide backbones
• Tertiary structure is determined by interactions among various side chains (R groups), including hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions, sometimes covalent bonds called disulfide bridges may reinforce the protein’s structure
• Quaternary structure results when a protein consists of multiple polypeptide chains, ex. Hemoglobin, collagen