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Proteins and Enzymes Proteins have many functions • They provide structural support in bones and muscles • They form parts of cell membranes • They function as hormones to regulate the body Proteins have many functions • They form antibodies to protect against infection • They increase the rate of chemical reactions Proteins are macromolecules. • They contain nitrogen, carbon, hydrogen, and oxygen (most also have sulfur) • The monomers of proteins are amino acids. Proteins are macromolecules. • Amino acids contain an amino group, a carboxyl group, and a variable R-group. • When the amino acids join, they form a polymer called a polypeptide. The monomers are held together by peptide bonds. • 20 different amino acids are found in nature. • Since the R-group varies, it allows for much variety. That is why proteins have so many functions. Proteins have four levels of organization. • This allows for the unique shape of proteins. • Shape is very important; if a protein is not the right shape, it will not work. Primary structure • A sequence of amino acids Secondary structure • α helix – coil held together by hydrogen bonding • β sheet – two or more regions of the polypeptide chain are parallel Tertiary Structure • Ionic bonding • Hydrophobic interactions • Disulfide bonding • Hydrogen bonding Hydrogen Bonding • http://programs.northlandcollege.edu/biology /Biology1111/animations/hydrogenbonds.htm l • This animation shows hydrogen bonding in water – but it is the same type of bonding in other molecules Quaternary Structure • Combination of two or more polypeptide chains – Ex: Hemoglobin consists of 2 alpha chains and 2 beta chains Enzymes – a special type of protein • Enzymes are biological catalysts, which work to speed up a chemical reaction. • Without enzymes, several reactions in cells would never occur or happen to slowly to be useful. Enzymes lower activation energy. • Activation energy is the energy needed to get a chemical reaction started. Effect of Enzymes • When activation energy is lowered, the reaction speeds up. Enzyme Action • Enzymes provide a site where reactants can be brought together to react. • This is site is called the active site. • The reactants are called the substrates. Enzyme Action • The shape of an enzyme is so specific that generally only one enzyme will work for one substrate. • Therefore, enzymes are said to fit together like a “lock and key.” Enzyme Action Since only the substrate changes during the reaction, the enzyme can be reused again and again. • Enzymes work best at specific temperatures and pH. • Heating can change the enzyme shape (denaturing) • The wrong pH affects the binding of the substrate to the enzyme. • Most enzymes in our body work best at 37°C (98.6°F) and at a pH between 6.5 to 7.5. High Salinity also disrupts the enzyme’s shape Induced-Fit Model • Says that enzymes and substrates don’t quite fit together perfectly • Enzyme conforms slightly to substrate, which aids the enzyme in changing the substrate’s structure Cofactors • Metal ions or coenzymes (often vitamins) • Shift electron arrangement in enzymesubstrate complex Enzyme Regulation • Most cells contain proteins that turn enzymes on or off. Allosteric Control • Molecule binds to enzyme (not at active site) and changes active site structure Allosteric Control Affect of substrate concentration Affect of enzyme concentration • Assumes unlimited amount of substrate • Eventually enzymes will run out of substrate to bind with, lowering the reaction rate