energy and enzymes

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© 2011 Pearson Education, Inc. 1000’s of reactions occur in living cells cells extract energy and use energy to perform work CELLULAR WORK : Metabolism Energy ATP Enzymes

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Enzyme 1 Enzyme 2 Enzyme 3 Reaction 1 Reaction 2 Reaction 3 Product Reactant A B C D each step is catalyzed by a specific enzyme Metabolic Pathways: An organism’s metabolism transforms matter and energy Metabolism - the totality of an organism’s chemical reactions

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Anabolic pathways - consume energy to build complex molecules from simpler ones Catabolic pathways - release energy by breaking down complex molecules into simpler ones

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Energy : the capacity to cause change Energy can be converted from one form to another Kinetic energy - associated with motion…..work in action Potential energy – what matter possesses due to location or structure Chemical energy - potential energy available for release in a chemical reaction Heat (thermal energy) - kinetic energy associated with random movement of atoms or molecules

Wingdings:

Figure 8.2 A diver has more potential energy on the platform than in the water. Diving converts potential energy to kinetic energy. Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water than on the platform. HEAT

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Potential Energy as Chemical Energy

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The Laws of Energy Transformation Isolated system - isolated from its surroundings Open system - energy and matter can be transferred between the system and its surroundings © 2011 Pearson Education, Inc. Organisms are open systems

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Chemical energy First Law of Thermodynamics - Energy can be transferred and transformed, but it cannot be created or destroyed (conservation of energy)

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Figure 8.3b Heat With every energy transfer or transformation, some energy is unusable, and lost as heat…….. Second Law of Thermodynamics Every energy transfer or transformation increases the entropy (randomness) of the universe

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Figure 8.3 (a) First law of thermodynamics (b) Second law of thermodynamics Chemical energy Heat Entropy = disorder or randomness Heat - has the most entropy in the universe Spontaneous processes occur without energy input For a process to occur without energy input it must increase the entropy of the universe

Figure 8.2:

• More free energy (higher G ) • Less stable • Greater work capacity In a spontaneous change • The free energy of the system decreases (  G  0) • The system becomes more stable • The released free energy can be harnessed to do work • Less free energy (lower G ) • More stable • Less work capacity During a spontaneous change Free energy (G) decreases and the stability of a system increases A process is spontaneous and can perform work when it is moving toward equilibrium Equilibrium is a state of maximum stability

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Free-Energy Change,  G the energy that is available to do work © 2011 Pearson Education, Inc. change in free energy (∆ G ) during a process is related to….. the change in enthalpy (total energy) (∆ H ) the change in entropy (∆ S ) the temperature (T) ∆ G = ∆ H – T ∆ S Processes with a positive ∆ G are not spontaneous Only processes with a negative ∆ G are spontaneous Spontaneous processes can be harnessed to perform work

The Laws of Energy Transformation:

Reactants Energy Products Progress of the reaction Amount of energy released (-  G  0) Free energy Exergonic reaction is spontaneous……… proceeds with a net release of free energy (“downhill”)

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Reactants Energy Products Amount of energy required (+  G  0) Progress of the reaction Free energy Endergonic reaction is NOT spontaneous absorbs free energy from its surroundings (“uphill”)

Figure 8.3b:

An isolated system - G  0  G  0 closed system - reactions eventually reach equilibrium (and then do no more work)

Figure 8.3:

Figure 8.7b An open system - G  0 Cells (organisms) are not isolated and are not in equilibrium cells are open systems – there is a constant flow of materials in and out

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Figure 8.7c A multistep open system - G  0 - G  0 - G  0 catabolic pathways in a cell release free energy in a series of reactions

Free-Energy Change, G:

Phosphate groups Adenine Ribose ATP (adenosine triphosphate) - the cell’s energy shuttle cells use ATP for energy coupling – using an exergonic process to drive an endergonic one

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Figure 8.8b Adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) Hydrolysis of ATP the exergonic ( -  G ATP ) reaction of ATP hydrolysis is used to drive endergonic reactions  G ATP =  7.3 kcal/mol

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Glutamic acid Ammonia Glutamine (b) Conversion reaction coupled with ATP hydrolysis Glutamic acid conversion to glutamine (a) (c) Free-energy change for coupled reaction Glutamic acid Glutamine Phosphorylated intermediate Glu NH 3 NH 2 Glu  G Glu = +3.4 kcal/mol ATP ADP ADP NH 3 Glu Glu P P i P i ADP Glu NH 2  G Glu = +3.4 kcal/mol Glu Glu NH 3 NH 2 ATP  G ATP =  7.3 kcal/mol  G Glu = +3.4 kcal/mol +  G ATP =  7.3 kcal/mol Net  G =  3.9 kcal/mol 1 2 ATP drives endergonic reactions by phosphorylating an intermediate Chemical Work

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Figure 8.10 Transport protein Solute ATP P P i P i ADP P i ADP ATP ATP Solute transported Vesicle Cytoskeletal track Motor protein Protein and vesicle moved Mechanical work: ATP binds to motor proteins and then is hydrolyzed. Transport work: ATP phosphorylates transport proteins.

Figure 8.7b:

Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP ADP P i H 2 O ATP is a renewable resource - Continuously regenerated via cellular respiration

Figure 8.7c:

Enzyme – Sucrase Sucrose (C 12 H 22 O 11 ) Glucose (C 6 H 12 O 6 ) Fructose (C 6 H 12 O 6 ) Catalyst = speeds up a reaction without being consumed by the reaction ENZYMES - catalysts that speed up metabolic reactions

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Figure 8.12 Transition state Reactants Products Progress of the reaction Free energy E A  G  O A B C D A B C D A B C D The Activation Energy Barrier initial energy needed to start a reaction is called the activation energy (E A )

Figure 8.8b:

Figure 8.13 Course of reaction without enzyme E A without enzyme E A with enzyme is lower Course of reaction with enzyme Reactants Products  G is unaffected by enzyme Progress of the reaction Free energy Enzymes Lower the E A Barrier

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Figure 8.14 Substrate Active site Enzyme Enzyme-substrate complex Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

Figure 8.10:

Figure 8.15-1 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. 1 2 Enzyme Active site

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Figure 8.15-2 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. Active site can lower E A and speed up a reaction. 1 2 3 Substrates are converted to products. 4 Enzyme Active site The active site can lower an E A barrier by………. Orienting substrates correctly Straining substrate bonds Providing a favorable microenvironment Covalently bonding to the substrate

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Figure 8.15-3 Substrates Substrates enter active site. Enzyme-substrate complex Enzyme Products Substrates are held in active site by weak interactions. Active site can lower E A and speed up a reaction. Active site is available for two new substrate molecules. Products are released. Substrates are converted to products. 1 2 3 4 5 6

Figure 8.12:

Effects of Local Conditions on Enzyme Activity An enzyme’s activity can be affected by………….. environmental factors, such as temperature and pH Chemicals that influence the enzyme © 2011 Pearson Education, Inc. Each enzyme has an optimal temperature and pH to function within Optimal conditions favor the most active shape for the enzyme molecule

Figure 8.13:

Figure 8.16a Optimal temperature for typical human enzyme (37°C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C) Temperature (°C) (a) Optimal temperature for two enzymes Rate of reaction 120 100 80 60 40 20 0

Figure 8.14:

Figure 8.16b Rate of reaction 0 1 2 3 4 5 6 7 8 9 10 pH (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme)

Figure 8.15-1:

Cofactors : enzyme helpers Cofactors may be inorganic (such as a metal in ionic form) or Be an organic cofactor - coenzyme (ex. vitamins) © 2011 Pearson Education, Inc.

Figure 8.15-2:

Figure 8.17 Normal binding Substrate Active site Enzyme Competitive inhibitor Noncompetitive inhibitor Noncompetitive inhibitors bind to another part of an enzyme, causing enzyme to change shape and making active site ineffective Competitive inhibitors bind to the active site of an enzyme and compete with the substrate

Figure 8.15-3:

Regulation of enzyme activity helps control metabolism © 2011 Pearson Education, Inc. Allosteric regulation – can either inhibit or stimulate an enzyme’s activity….. a regulatory molecule binds to a protein at one site and affects the protein’s function at another site enzymes have active and inactive forms binding of an activator stabilizes the active form of the enzyme binding of an inhibitor stabilizes the inactive form of the enzyme

Effects of Local Conditions on Enzyme Activity:

Figure 8.19a Regulatory site Allosteric enzyme Active site Active form Activator Stabilized active form Nonfunctional active site Inactive form Inhibitor Stabilized inactive form

Figure 8.16a:

Figure 8.19b Inactive form Substrate Stabilized active form Cooperativity : another type of allosteric activation that can amplify enzyme activity One substrate primes an enzyme to act on additional substrates more readily binding by substrate at one active site catalyzes binding at other active sites

Figure 8.16b:

Figure 8.21 Active site available Isoleucine used up by cell Feedback inhibition Active site of enzyme 1 is no longer able to catalyze and; pathway is switched off. Isoleucine binds to allosteric site. substrate (threonine) Enzyme 1 Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine) Feedback inhibition - end product shuts down the pathway

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Figure 8.22 Mitochondria The mitochondria matrix contains enzymes in solution that are involved in one stage of cellular respiration. Enzymes for other stages of cellular respiration are embedded in the inner membrane. 1  m

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