ENERGY

Energy• capacity to perform work• done when objects are moved against opposing

forces & things move in directions in which they would not have moved if left alone

• body needs energy• cells are biggest users of energy in the body• need energy to make complex molecules from

monomer building blocks-anabolic reactions• need energy to break down macromolecules-

catabolic reactions to obtain energy to do all of the activities they need to do everyday

First Law of Thermodynamics• energy cannot be destroyed nor created• energy can be converted from one form to

another• plants convert energy in sunlight into

chemical energy life forms use to perform activities of life

• can’t use energy over & over • each time there is energy transfer some

energy becomes unusable

Forms of Energy• Kinetic energy

–energy of motion

• Potential energy

–stored energy

–energy an object has as result of its locomotion or structure

Forms of Energy

Energy Flow• energy flows into our

ecosystem as sunlight

• kinetic energy (from sun) is transformed into chemical energy-potential energy of food & fuels by photosynthesis

Energy Flow• animals

consume food products to provide ATP or energy for cells to perform work

Endergonic Reactions• yield potential energy

• require input of energy

• products acquire more energy than reactants

• energy is stored in covalent bonds of products

• photosynthesis is an endergonic reaction

Exergonic Reactions• release energy • reactions begin with

reactants whose covalent bonds contain more energy than in products & release energy to the environment

• occur in cells of body• cellular respiration• oxygen is used to convert

chemical energy stored in fuel molecules (glucose) to chemical energy (ATP) cell uses to carry on its processes

• Glucose + O2 CO2 + H2O

ATP-Adenosine Triphosphate• provides energy for cellular work• consists of• adenine

– nitrogenous base• ribose

– five carbon sugar• called adenosine• 3 PO4 groups attached-triphosphate part• phosphate bonds are unstable • can be easily broken by hydrolysis in

exergonic reactions• each PO4 group released from ATP

yields 7Kcal of energy• one phosphate group removed• ATPADP + pi + 7Kcal of energy

– adenosine diphosphate + inorganic phosphate + energy

• another phosphate removed• AMP + pi + 7Kcal of energy

– adenosine monophosphate

Cellular Metabolism• every working cell in body

performs exergonic & endergonic reactions

• sum-cellular metabolism• energy released from

exergonic reactions is used to drive endergonic reactions

• energy coupling• ATP functions in energy

coupling

Energy Coupling

Factors in Chemical Reactions• many molecules in body

store tremendous amount of potential energy

• do not spontaneously break down into smaller components

• to initiate reactions reactants need to overcome an energy barrier

• amount of energy that compound must absorb before chemical reaction can begin-activation energy

• requires a catalyst• something to speed rate of

reaction

Enzymes• speed rate of

reactions

• lower activation energy

• globular proteins• names typically end in

–ase• each has a unique 3-

D shape• shape determines

which reactions enzyme can catalyze

Enzymes• specific reactant for

specific enzyme-substrate

• fits into specific area-active site

• once product forms• enzyme detaches

from active site• free to start another

reaction

Enzyme Action

Saturation Limit• reaction rate is proportional to

concentration of substrate & concentration of enzyme

• enzyme must meet with specific amount of substrate before catalysis can begin

• higher substrate concentrations more frequently encountered by enzyme

• when substrate concentrations are high enough so every enzyme molecule is cycling through its reaction sequence at top speed further increase in substrate concentration will not effect rate of reaction unless more enzyme is added

• substrate concentration at which rate of a reaction is maximum is saturation limit

Regulation of Enzymatic Reactions• many variables turn

enzymes on & off to control reaction rates

• enzymes are proteins• protein shapes can be

changed by the environment

• Temperature• Salt concentration• pH

Regulators of Enzymatic Activity• Cofactors

– ions or molecules that bind to enzyme before substrate can bind

• allows enzymes to be active sometimes & inactive at other times

• several important inorganic cofactors-zinc, iron & copper

• organic cofactors are coenzymes

• most made from vitamins or are vitamins

Inhibition of Enzymatic Activity• chemicals that interfere with

enzyme function-inhibitors• competitive inhibitors

– fit into active sites so real substrate cannot

• noncompetitive inhibitors– bind at sites other than

active site – changes enzyme’s

shape– causes active site to no

longer recognize substrate

Inhibition• Reversible inhibitors

– can serve a regulatory function

– turn enzyme on when needed

– turn it off when not• Irreversible inhibitors

– kill enzyme function– poisons– block metabolic

processes that are essential to survival

Irreversible Inhibition• Penicillin• inhibits enzymes in

bacteria needed to make cells walls

• since humans do not have this enzyme penicillin can be used to kill the bug without effecting human cells