Chemical Reactions Important to Physiology- Break Down, Build Up Decomposition reaction (catabolism): AB A + B Synthesis reaction (anabolism): A + B AB Exchange reaction (reversible): AB A + B Catabolism-break down polysaccharides to monomers (glucose) for absorption into bloodstream Anabolism-build proteins from monomers (amino acids) for growth and development Exchange – carry oxygen in blood stream on hemoglobin and release at tissue level

Energy In, Energy Out Exergonic reactions: Endergonic reactions: produce more energy than they use Example: Cellular respiration Endergonic reactions: use more energy than they produce Example: hydrolytic reactions require energy to use water molecules to break apart macromolecules during digestion Most chemical reactions that sustain life cannot occur unless the right enzymes are present

Materials in Reactions Reactants: materials going into a reaction Products: materials coming out of a reaction Enzymes: proteins that lower the activation energy of a reaction

Enzymes control metabolism by lowering Activation Energy Chemical reactions in cells cannot start without help Activation energy gets a reaction started Figure 2–7

Lower the activation energy, increase the speed of a reaction (millions of reactions per minute!)

Shape and Function Protein function is based on shape Shape is based on sequence of amino acids Denaturation: loss of shape and function due to heat or pH

Enzyme Names Often named for the reaction they catalyze; usually end in -ase (e.g., hydrolases, oxidases)

Enzymes Enzymes are catalysts: Specificity: Regulation: proteins that lower the activation energy of a chemical reaction are not changed or used up in the reaction Specificity: one enzyme catalyzes one reaction Regulation: the ability to turn off and on

How Enzymes Work Figure 2–21

How Enzymes Work Substrates: Active site: Product reactants in enzymatic reactions Active site: a location on an enzyme that fits a particular substrate Product the end result of the enzymatic reaction

ADP and ATP (modified RNA nucleotides) adenosine diphosphate (ADP): 2 phosphate groups di = 2 adenosine triphosphate (ATP): 3 phosphate groups tri = 3

Phosphorylation • Adding a phosphate group to ADP with a high-energy bond to form the high-energy compound ATP ATPase: (ATP synthase) the enzyme that catalyzes phophorylation

The Energy Molecule Chemical energy stored in phosphate bonds Figure 2–24