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Energy Flow in a Cell: Types of Energy and Chemical Reactions

Learn about the different types of energy and chemical reactions in a cell, including exergonic and endergonic reactions, and how energy is carried between coupled reactions.

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Energy Flow in a Cell: Types of Energy and Chemical Reactions

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  1. Chapter 5 Energy Flow in the Life of a Cell

  2. 5.1 What Is Energy? • Energy is the capacity to do _______. • Synthesizing molecules • Moving objects • Generating heat and light • Types of energy • ________: energy of movement • ________: stored energy • Kinetic energy can be converted to potential energy and vice versa Fig. 5-1

  3. 5.1 What Is Energy? • First Law of Thermodynamics • “Energy cannot be created nor destroyed, but it can change its form.” • Total amount of energy in the universe remains constant. • Examples • Gas in car movement and heat • Food fueling a runner  movement and heat

  4. 5.1 What Is Energy? • Second Law of Thermodynamics • “When energy is converted from one form to another, the amount of energy that is in a useful form decreases.” • The total energy is maintained. • No process is 100% efficient. • Example: The kinetic energy of the car moving is less than the amount of potential energy in the gasoline b/c the gas not only moved the car, but also heated the engine, exhaust system, air, and pavement.

  5. 5.1 What Is Energy? • Matter tends to become less organized. • Regions of concentrated energy tend to be more organized than those where energy is widely dispersed. • Example: The eight carbon atoms in a molecule of gasoline have a more orderly arrangement than the eight separate carbon dioxide molecules moving around when the molecule of gasoline burns. • ___________: the spontaneous reduction in ordered forms of energy, and an increase in randomness and disorder as reactions proceed • Entropy can be overcome by adding more energy.

  6. 5.1 What Is Energy? • All chemical reactions cause the amount of usable energy to decrease, leading to increased randomness and disorder • In order to keep useful energy flowing in ecosystems where the plants and animals produce more random forms of energy, new energy must be brought in. • Sunlight provides an unending supply of new energy to power all plant and animal reactions, leading to increased entropy. Fig. 5-2

  7. 5.2 How Does Energy Flow In Chemical Reactions? • Chemical reaction: the conversion of one set of chemical substances (___________) into another (___________). • ______________ reaction: a reaction that releases energy; the reactants contain more energy than the products • ______________ reaction: a reaction that requires energy input from an outside source; the products contain more energy than the reactants

  8. 5.2 How Does Energy Flow In Chemical Reactions? • Exergonic reaction energyreleased + reactants + products (a) Exergonic reaction Fig. 5-3a

  9. 5.2 How Does Energy Flow In Chemical Reactions? • Exergonic reactions _________ energy. • Example: sugar burned by a flame in the presence of oxygen produces carbon dioxide (CO2) and water • Sugar and oxygen contain more energy than the molecules of CO2 and water. • The extra energy is released as heat.

  10. 5.2 How Does Energy Flow In Chemical Reactions? • Burning glucose releases energy. energyreleased C6H12O6 + 6 O2 (glucose) (oxygen) 6 CO2 6 H2O + (water) (carbondioxide) Fig. 5-4

  11. 5.2 How Does Energy Flow In Chemical Reactions? • Endergonic reaction energyused + products + reactants (b) Endergonic reaction Fig. 5-3b

  12. 5.2 How Does Energy Flow In Chemical Reactions? • Endergonic reactions require an ________ of energy. • Example: sunlight energy + CO2 + water in photosynthesis produces sugar and oxygen • The sugar contains far more energy than the CO2 and water used to form it.

  13. 5.2 How Does Energy Flow In Chemical Reactions? • Photosynthesis requires energy. energy C6H12O6 + 6 O2 (glucose) (oxygen) 6 CO2 + 6 H2O (water) (carbondioxide) Fig. 5-5

  14. 5.2 How Does Energy Flow In Chemical Reactions? • All reactions require an initial input of energy. • The initial energy input to a chemical reaction is called the _____________ energy. Even exergonic reactions require activation energy. Activationenergycapturedfromsunlight Activation energy neededto ignite glucose high glucose Energy level of reactants glucose + O2 energycontentofmolecules Energy level of reactants CO2 + H2O CO2 + H2O low progress of reaction progress of reaction (a) (b) Burning glucose (sugar): an exergonic reaction Photosynthesis: an endergonic reaction Fig. 5-6

  15. 5.2 How Does Energy Flow in Chemical Reactions? • ____________ reactions: Endergonic reactions obtain energy from exergonic, energy-releasing reactions. • An exergonic reaction provides the energy to needed to drive an endergonic reaction • Example: the exergonic reaction of burning gasoline in a car provides the endergonic reaction of moving the car • Example: exergonic reactions in the sun release light energy used to drive endergonic sugar-making reactions in plants

  16. 5.3 How Is Energy Carried Between Coupled Reactions? • The exergonic and endergonic parts of coupled reactions often occur in different parts of the cell, so a messenger is needed to transfer the energy. This is done by ________-_________ molecules. • ATP (adenosine triphosphate) is the main energy carrier molecule in cells, and provides energy for many endergonic reactions.

  17. 5.3 How Is Energy Carried Between Coupled Reactions? • ATP is made from ADP (adenosine diphosphate) and phosphate plus energy released from an exergonic reaction (e.g., glucose breakdown) in a cell. energy A P P P ATP + A P P P phosphate ADP Fig. 5-7

  18. 5.3 How Is Energy Carried Between Coupled Reactions? • ATP is the principal energy carrier in cells. • ATP stores energy in its phosphate bonds and carries the energy to various sites in the cell where energy-requiring reactions occur. • ATP’s phosphate bonds then break yielding ADP, phosphate, and energy. • This energy is then transferred to the energy-requiring reaction.

  19. 5.3 How Is Energy Carried Between Coupled Reactions? • Breakdown of ATP releases energy. energy A P P P ATP + A P P P ADP phosphate Fig. 5-8

  20. 5.3 How Is Energy Carried Between Coupled Reactions? • Coupled reactions: exergonic fuelling endergonic glucose P A P P exergonic(glucose breakdown) protein endergonic(ATP synthesis) exergonic(ATP breakdown) endergonic(protein synthesis) CO2 + H2O + heat + A P P P aminoacids Fig. 5-9

  21. 5.3 How Is Energy Carried Between Coupled Reactions? • Besides ATP, other carrier molecules transport energy within a cell. • __________ carriers capture the energetic electrons to which energy is transferred in some exergonic reactions. • Energized electron carriers then donate these energy-containing electrons to endergonic reactions. • Nicotinamide adenine dinucleotide (NAD+) • Flavin adenine dinucleotide (FAD)

  22. 5.4 How Do Cells Control Their Metabolic Reactions? • Cell metabolism: the multitude of chemical reactions going on at any specific time in a cell (___________ & ____________) • Metabolic pathways: the sequence of cellular reactions in which the products of one reaction are the reactants for the next reaction. Final products Initial reactant Intermediates A PATHWAY 1 D E B C enzyme 1 enzyme 2 enzyme 3 enzyme 4 G F PATHWAY 2 enzyme 5 enzyme 6 Fig. 5-12

  23. 5.4 How Do Cells Control Their Metabolic Reactions? • At body temperature, many spontaneous reactions proceed too slowly to sustain life. • A reaction can be controlled by controlling its activation energy (the energy needed to start the reaction). • At body temperature, reactions occur too slowly because their activation energies are too high. • Molecules called catalysts are able to gain access to energy that is not produced spontaneously.

  24. 5.4 How Do Cells Control Their Metabolic Reactions? • ___________ are molecules that speed up a reaction by reducing the activation energy • They speed up reactions that would occur anyway, if their activation energy could be surmounted. • Catalysts are not altered by the reaction. high Activation energywithout catalyst Activation energywith catalyst energycontentofmolecules reactants products low progress of reaction Fig. 5-13

  25. 5.4 How Do Cells Control Their Metabolic Reactions? • __________ are biological catalysts. • Almost all enzymes are __________. • Enzymes are highly specialized, generally catalyzing only a single reaction. • In metabolic pathways involving multiple reactions, each reaction is catalyzed by a different enzyme.

  26. 5.4 How Do Cells Control Their Metabolic Reactions? • The function of enzymes is closely related to their structure. • Enzymes have an ________ site where the reactant molecules, called __________, enter and undergo a chemical change as a result. • The specificity of an enzyme reaction is due to the distinctive shape of the active site, which only allows proper substrate molecules to ener

  27. 5.4 How Do Cells Control Their Metabolic Reactions? • How does an enzyme catalyze a reaction? • Substrates enter the enzyme’s active site. • Shape of substrates and enzyme change to fit together better (handshake). • Chemical reaction/bonding occurs between the substrates. • The substrates change into a new form that will not fit the active site, and so are released. • Enzyme can accept new substrates

  28. 5.4 How Do Cells Control Their Metabolic Reactions? • The cycle of enzyme–substrate interactions substrates active siteof enzyme enzyme 1 Substrates enterthe active site in aspecific orientation The substrates andactive site change shape,promoting a reactionbetween the substrates The substrates, bondedtogether, leave the enzyme;the enzyme is ready for anew set of substrates 3 2 Fig. 5-14

  29. 5.4 How Do Cells Control Their Metabolic Reactions? • Enzyme structure substrate Many enzymes haveboth active sites andallosteric regulatorysites active site enzyme allostericregulatory site (a) Enzyme structure Fig. 5-15a

  30. 5.4 How Do Cells Control Their Metabolic Reactions? • _____________ regulation can increase or decrease enzyme activity. • In allosteric regulation, an enzyme’s activity is modified by a regulator molecule. • The regulator molecule binds to a special regulatory site on the enzyme separate from the enzyme’s active site. • Binding of the regulator molecule modifies the active site on the enzyme, causing the enzyme to become more or less able to bind substrate. • Thus, allosteric regulation can either promote or inhibit enzyme activity.

  31. 5.4 How Do Cells Control Their Metabolic Reactions? • Allosteric inhibition An allosteric regulatormolecule causes theactive site to changeshape, so the substrateno longer fits allostericregulatormolecule (b) Allosteric inhibition Fig. 5-15b

  32. 5.4 How Do Cells Control Their Metabolic Reactions? • ___________ inhibitors decrease enzyme activity • They block the entry of a substrate by occupying the active site • Can be temporary or permanent. • These molecules compete with the substrate for access to the active site, and control the enzyme by competitive inhibition. • Some poisons are competitive inhibitors. • Concentration of substrates vs competitors affects which is more likely to bind

  33. 5.4 How Do Cells Control Their Metabolic Reactions? • Competitive inhibition A competitive inhibitor moleculeoccupies the active site andblocks entry of the substrate Fig. 5-16

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