Chapter 6: Metabolism: Energy and Enzymes

I.  energy: the capacity to do work

            A.  types of energy: mechanical, electrical, thermal, chemical

                        1.  kinetic energy: the energy of motion

                        2.  potential energy: stored energy

            B.  energy laws

                        #1 - "law of conservation of energy" - Energy can neither be

                                created nor destroyed

                        #2 - Energy can be transformed from one form to another

                                    a.  some useful energy is lost in the form of heat

                                    b.  energy flow is one way, not recycled

                                    c.  sun: source of new supply of energy on earth, 2%

                                         captured in plants

                        #3 - entropy: amount of disorder, occurs naturally, is always

                                increasing

II.  metabolism: chemical reactions that occur in living things

            A.  free energy: the amount of energy available to do work after a

                chemical reaction has taken place

                        1.  exergonic: energy is released

                        2.  endergonic: input of energy

                        3.  coupling reactions: energy released by an exergonic reaction is

                             used to drive an endergonic reaction

            B.  ATP (adenosine triphosphate): common energy currency in the cell

                        1.  functions of ATP

                                    a.  chemical: provides energy to synthesize molecules in the

                                         cell

                                    b.  transport: provides energy to pump substances across

                                         the plasma membrane

                                    c.  mechanical: provides energy for movement, muscle

                                         contraction, cilia, flagella, etc.

                        2.  structure of ATP: adenine-ribose-phosphate-phosphate-

                             phosphate

                        3.  structure of ADP: adenine-ribose-phosphate-phosphate

                        4.  phosphorylation: ATP <-> energy + ADP + P

III.  metabolic pathways: a series of linked chemical reactions A -> B-> C-> D-> E

            A.  substrate or reactant: on the left side of a reaction

            B.  product or result of a reaction

            C.  enzymes -protein catalysts that speed up specific reactions without

                  being used up, at lower temperatures, often named by adding "ase" to

                  the name of the substrate

                        1.  energy of activation: energy necessary for a reaction to take

                             place, enzymes lower this to body temperature

                        2.  enzyme-substrate complex: when an enzyme and substrate

                             combine

                        3.  active site: the part of the enzyme where the specific substrate

                             fits

                        4.  induced fit model: enzyme changes shape to lock around the

                             substrate

            D.  factors that affect enzymatic speed

                        1.  temperature: warm temperatures increase speed of reaction,

                             lower temperatures slow it down

                        2.  denatured: boiling causes changes of shape in the enzyme and

                              it no longer works

                        3.  pH: every enzyme has an optimal pH where it works best,

                            extreme pH also denatures enzymes

                        4.  amount of enzyme: greater concentration speeds up the

                             reaction

                                    a.  controlled by genes to turn on or slow production of

                                         enzymes

                                    b.  activate or deactivate enzyme, often activated by

                                         phosphorylation

                        5.  inhibition: a way cells regulate enzyme activity

                                    a.  competition: another molecule competes with the active

                                         site of the enzyme, the shape is very close to being alike

                                    b.  noncompetitive: a molecule binds with an enzyme but not

                                         at the active site

                                                1) allosteric site: "other site", changes shape of an

                                                    enzyme so it doesn't work

                                    c.  negative feedback: the product binds to the active site

                                         and shuts down production of more product

                        6.  ex; poisons, penicillin

            E.  cofactors: nonprotein assistant for enzymes, ions (Mg, K, Ca, Fe)

            F.  coenzymes: organic molecules that serve as carriers for chemical

                 groups or electrons, may be a vitamin, ex) NAD from niacin, FAD from

                 riboflavin (B₂)

IV.  metabolic pathways and living things

            A.  photosynthesis: solar energy + CO₂ + H₂O -> C₆H₁₂O₆ + O₂

            B.  aerobic respiration: C₆H₁₂O₆ + O₂ -> CO₂ + H₂O + energy

            C.  electron transport system: passes H⁺ and electrons along membranes

                  in chloroplasts and mitochondria

                        1.  carriers are coenzymes: NAD⁺, NADP⁺, and FAD⁺²

                        2.  energy is transferred from high energy to low

                        3.  chemiosmotic theory: carriers pump H⁺ across a membrane,

                             causing a H+ gradient, and generating ATP