Chapter 6 Metabolism: Energy and Enzymes Biology 2 AP

Living Things Need... Living things need to maintain their organization carry on life’s activities Living things need a source of organic food make for themselves feed on plants or animals All living systems require constant input of free energy

Food Provides nutrient molecules Used as a source of energy make ATP fuels chemical reactions in cells Used for building blocks to make other molecules

Metabolism All the chemical reactions that occur in a cell Enzymes protein molecules speed up metabolic reactions at low temperatures

Energy Ability to do work Many forms light kinetic (energy of motion) potential (stored energy) chemical

Laws of Thermodynamics 1st Law Energy cannot be created or destroyed, only changed from one form to another chemical energy in coal changed to heat energy which is converted to electrical energy in a coal burning power plant

2nd Law of Thermodynamics Energy cannot be changed from one form to another w/o losing some useable energy no energy conversion is 100% efficient lose energy as heat (which is dissipated and “lost” to the environment)

Entropy Measure of randomness or disorder Organization has low entropy A mess has high entropy Natural tendency increase disorder get messier increase entropy Entropy of the universe is increasing

Entropy and Energy Constant input of energy needed to maintain organization to reduce entropy of a system Energy put in goes through many conversions heat is given off entropy of universe increases

Chemical Reactions Reactants Products A + B ---> C + D substances that participate in a reaction Products substances formed as a result of a reaction A + B ---> C + D A and B are reactants C and D are products

Spontaneous Chemical Reactions occurs w/o input of energy Free Energy energy available to do work after a chemical reaction has occurred Organisms capture and store free energy for use in biological processes

DG (Gibbs Free Energy) “Delta” G or DG change in the free energy of a system -DG (Negative) products have less free energy than the reactants spontaneous chemical reactions have a negative DG

Exergonic Reactions Negative DG Energy is given off or released

Endergonic Reactions Positive DG Energy is put in for the reaction to occur

DG = 0 Reversible reaction Reaction is at equilibrium How to make a reaction at equilibrium “go?” the product will be used as a reactant in another reaction reaction will make more product to try to reach equilibrium reaction is driven forward

Coupled Reactions Many rxns in the body are endergonic require energy where will the energy come from? ATP  ADP + P is exergonic releases energy

Coupled Reactions Energy released by an exergonic reaction is used to make an endergonic reaction go ATP  ADP + P is coupled to endergonic reactions overall reaction becomes exergonic some of the energy released from the breakdown of ATP is lost as heat

ATP supply Breakdown of glucose during cellular respiration provides energy builds up ATP supply in mitochondria only 39% of free energy in glucose is used to make ATP rest of energy is lost as heat

ATP – Energy for Cells Energy Currency of Cells Used to provide energy for the cells ATP  ADP + P provides just enough energy for most biological reactions can be used for many different types of reactions very little energy is wasted when ATP breakdown is coupled w/ endergonic reactions

Function of ATP Supplies energy for chemical work to transport or pump substances across plasma membrane for mechanical work muscle contraction cilia and flagella movement movement of chromosomes

ATP Structure A nucleotide nitrogen base: adenine sugar: ribose adenine + ribose: adenosine 3 phosphate groups ATP  ADP + P phosphate group is easy to remove gives off 7.3 kcal/mole

Metabolic Pathways Chemical rxns in cells are part of a metabolic pathway series of linked reactions begin w/ a reactant end w/ a product many steps in between one reaction leads to another reaction

Metabolic Pathways AB BC CD DE EF FG Overall: AG

Enzymes Each step in a metabolic pathway is catalyzed by an enzyme protein molecule organic catalyst speeds up chemical reactions w/o getting used up brings molecules together to cause a reaction Substrate reactant in an enzyme catalyzed reaction

Activation Energy Minimum energy needed for a reaction to take place need energy to break bonds can heat a reaction to obtain enough energy increases # of molecules that will have enough energy to react increases # of effective collisions

Enzymes and Activation Energy Enzymes lower the activation energy of a reaction less energy is needed for a reaction to take place reaction occurs faster more molecules have enough energy to react

Enzymes and Activation Energy

Enzyme-Substrate Complex Enzyme forms a complex w/ the substrate substrate fits in the active site of an enzyme active site actually changes shape to fit substrate (induced fit model vs. old lock and key model)

Enzyme-Substrate Complex Some enzymes take part in the reaction break bonds in the substrate trypsin digests proteins by breaking peptide bonds breaks peptide bond introduces water Product(s) is released Active site returns to original state, ready to bind another substrate molecule

Enzyme-Substrate Complex

One Reaction – One Enzyme Presence or absence of an enzyme determines the reaction that will take place For every reaction, there is one specific enzyme to catalyze that reaction enzyme is named for their substrates enzyme that digests lipids: lipase enzyme that digests urea: urease name of enzyme ends in “-ase”

Factors Affecting Enzyme Speed Enzymatic reactions happen very rapidly Breakdown of hydrogen peroxide 600,000 times faster w/ catalase than w/o catalase Speed depends on substrate & enzyme concentration temperature pH

Substrate Concentration More substrate, increased enzyme activity more collisions between enzyme and substrate Maximum rate of reaction when all of the enzymes’ active sites are filled

Temperature and Enzymes As temperature increases, enzyme activity increases more effective collisions between enzyme and substrate molecules After a certain temperature enzyme activity decreases enzyme has become denatured shape of enzyme changes! cannot bind substrate

Temperature and Enzymes

pH and Enzymes Each enzyme has an optimum pH fastest rate enzyme has its normal configuratation When pH changes, R groups are affected affect H-bonding between R groups affect charges on R groups changes shape of enzyme may even denature enzyme permanently

Unifying Theme: Class Discussion Thus, “What is Relationship of Structure to Function” in the case of enzymes? Active site & substrate Optimum temperature and pH Denaturation Interactions between molecules affect their structure and function

Enzyme Concentration Control enzyme activity activate enzyme when needed sometimes an enzyme is phosphorylated Cell regulates which enzymes are present and/or active

Enzyme Inhibition Active enzyme is prevented from combining with its substrate Competitive inhibition a molecule, similar in shape to substrate, binds to active site blocks active site so substrate cannot bind Factors Affecting Enzymes

Enzyme Inhibition Allosteric Inhibition (a type of Noncompetitive molecule binds to the enzyme, but not at the active site binds to an allosteric site binding causes a change in the enzyme’s shape substrate cannot bind to active site Factors Affecting Enzymes

Feedback Inhibition Regulate the activity of an enzyme with its product Lots of product Product binds competitively at the active site As product is used up, less product binds to the active site reduce inhibition

Feedback Inhibition Regulate metabolic pathways final product inhibits the first enzyme of the pathway to shut down the entire pathway Poisons are often enzyme inhibitors cyanide inhibits an essential enzyme to all cells penicillin blocks the active site for an enzyme found in bacteria

Enzyme Cofactors Necessary ions or molecules needed for enzyme to function properly inorganic or organic not protein Assist enzyme May accept or contribute atoms to a reaction

Vitamins Small organic molecules Needed in trace amounts in diet Aid in the synthesis of coenzymes Becomes part of the coenzyme’s structure Niacin is part of coenzyme NAD+ B12 is part of coenzyme FAD Vitamin deficiency results in a lack of coenzyme enzyme activity is affected vitamin-deficiency symptoms result