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Chapter 6 Metabolism: Energy and Enzymes
Biology 2 AP
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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
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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
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Metabolism All the chemical reactions that occur in a cell Enzymes
protein molecules speed up metabolic reactions at low temperatures
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Energy Ability to do work Many forms light kinetic (energy of motion)
potential (stored energy) chemical
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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
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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)
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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
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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
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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
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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
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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
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Exergonic Reactions Negative DG Energy is given off or released
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Endergonic Reactions Positive DG
Energy is put in for the reaction to occur
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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
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Coupled Reactions Many rxns in the body are endergonic
require energy where will the energy come from? ATP ADP + P is exergonic releases energy
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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
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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
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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
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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
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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
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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
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Metabolic Pathways AB BC CD DE EF FG Overall: AG
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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
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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
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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
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Enzymes and Activation Energy
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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)
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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
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Enzyme-Substrate Complex
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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”
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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
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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
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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
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Temperature and Enzymes
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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
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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
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Enzyme Concentration Control enzyme activity
activate enzyme when needed sometimes an enzyme is phosphorylated Cell regulates which enzymes are present and/or active
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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
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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
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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
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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
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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
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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
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