Energy Flow in the Life of a Cell

Figure: 05-00CO Title: Runners convert energy. Caption: The bodies of these runners are efficiently converting energy stored in fats and carbohydrates to the energy of movement and heat.

II. The nature of energy A. Energy undergoes transitions in forms 1. Potential energy—stored energy 2. Kinetic energy—energy of movement 3. Mechanical, chemical, electrical

II. The nature of energy B. Properties of energy 1. First law of thermodynamics a. Total energy remains constant in a closed system b. Energy cannot be created or destroyed

II. The nature of energy B. Properties of energy (cont.) 2. Second law of thermodynamics a. In an isolated system, any change causes the quantity of concentrated, useful energy to decrease b. Energy is converted from more useful to less useful forms

II. The nature of energy B. Properties of energy (cont.) 2. Second law of thermodynamics c. Organization of matter and energy 1) Concentrated energy is more ordered (complex) chemically 2) Entropy—all processes in an isolated system result in an increase in randomness and disorder

Exergonic reaction reactants products Figure: 05-01UN01 Title: An exergonic reaction. Caption: reactants products

Endergonic reaction products reactants Figure: 05-01UN02 Title: An endergonic reaction. Caption: products reactants

III. Energy use in living things A. Energy is stored in the chemical bonds of biological molecules

glucose oxygen carbon dioxide water Figure: 05-01UN03 Title: Burning sugar releases energy. Caption: oxygen carbon dioxide water

III. Energy use in living things C. Energy releasing chemical reactions are exergonic 1. High energy reactants  low energy products

water carbon dioxide glucose oxygen Figure: 05-01UN03 Title: Burning sugar releases energy. Caption: oxygen

III. Energy use in living things D. Endergonic reactions require an energy input 1. Low energy reactants  high energy products 2. Do endergonic reactions create energy? 3. How can the product(s) of an endergonic reaction have more energy than the reactants without violating the Laws of Thermodynamics?

glucose oxygen carbon dioxide water Figure: 05-01UN04 Title: Photosynthesis requires energy. Caption: glucose oxygen carbon dioxide water

III. Energy use in living things E. Chemical reactions and activation energy Why does a match not spontaneously burn?

activation energy needed Burning glucose (sugar): an exergonic reaction activation energy needed to ignite glucose Figure: 05-02a Title: Energy relations in exergonic and endergonic reactions. Caption: (a) An exergonic (“downhill”) reaction, such as the burning of sugar, proceeds from high-energy reactants (here, glucose) to low-energy products (CO2 and H2O). The energy difference between the chemical bonds of the reactants and products is released as heat. To start the reaction, however, an initial input of energy, the activation energy, is required.

Photosynthesis: an endergonic reaction (b) Photosynthesis: an endergonic reaction glucose Figure: 05-02b Title: Energy relations in exergonic and endergonic reactions. Caption: (b) An endergonic (“uphill”) reaction, such as photosynthesis, proceeds from low-energy reactants (CO2 and H2O) to high-energy products (glucose) and therefore requires a large input of energy, in this case from sunlight.

III. Energy use in living things F. Coupling of exergonic and endergonic reactions 1. Exergonic reaction provides energy to drive endergonic reactions 2. How is the energy that is released from an exergonic reaction harnessed and directed to drive its related endergonic reaction?

III. Energy use in living things F. Coupling of exergonic and endergonic reactions (cont.) 3. Energy carrier molecules (energy taxis) ATP and electron carrier molecules

ATP synthesis: Energy is stored in ATP Figure: 05-02UN01 Title: ATP synthesis. Caption: ATP ADP phosphate

ATP breakdown: Energy of ATP is released Figure: 05-02UN02 Title: ATP breakdown. Caption: ATP ADP phosphate

contracted muscle contracted muscle Exergonic reaction: Endergonic reaction: contracted muscle relaxed muscle Coupled reaction: Figure: 05-03 Title: A coupled reaction. Caption: The exergonic reaction of ATP breakdown must precede the endergonic reaction of muscle movement. relaxed muscle contracted muscle

breakdown of ATP is used to power protein synthesis. Energy released from breakdown of glucose is transferred to ATP. Energy released from breakdown of ATP is used to power protein synthesis. exergonic (glucose breakdown) endergonic (ATP synthesis) exergonic (ATP breakdown) endergonic (protein synthesis) Figure: 05-04 Title: Coupled reactions give off heat. Caption: The overall reaction is “downhill”: More energy is produced by the exergonic reaction than is needed to drive the endergonic reaction. The extra energy is released as heat. overall exergonic “downhill” reaction

exergonic (energized reaction carrier) (depleted endergonic carrier) Figure: 05-05 Title: Electron carriers. Caption: An electron-carrier molecule such as NAD+ picks up an electron generated by an exergonic reaction and holds it in a high-energy outer electron shell. The electron is then deposited, energy and all, with another molecule to drive an endergonic reaction, typically the synthesis of ATP. overall exergonic “downhill” reaction

Initial reactant Intermediates Final products PATHWAY 1 PATHWAY 2 Figure: 05-06 Title: Simplified view of metabolic pathways; Caption: The original reactant molecule, A, undergoes a series of reactions. The product of each reaction serves as the reactant for the next reaction in the pathway or for a reaction in another pathway. PATHWAY 2

IV. Chemical reactions in living organisms need to be catalyzed A. Activation energy requirements for all the chemical reactions occurring in an organism are too high B. Catalysts reduce activation energy requirements

activation energy without catalyst activation energy with catalyst Figure: 05-07 Title: Catalysts reduce activation energy. Caption:

IV. Chemical reactions in living organisms need to be catalyzed C. Enzymes catalyze reactions in living organisms 1. Bring reactant molecules close together 2. Make bonds easier to break

IV. Chemical reactions in living organisms need to be catalyzed C. Enzymes catalyze reactions in living organisms (cont.) 3. Enzymes are very specific a. Specificity is based on shape of enzyme and substrate b. Lock and key analogy

IV. Chemical reactions in living organisms need to be catalyzed C. Enzymes catalyze reactions in living organisms (cont.) 4. Most enzymes function as parts of complex, regulated biochemical pathways 5. Most enzymes are proteins Mutation and loss of enzyme function

substrates enzyme substrates enzyme substrates enzyme 3 Substrates, bonded together, leave enzyme; enzyme is ready for new set of substrates. active site of enzyme 1 Substrates enter active site in a specific orientation. 2 Substrates and active site change shape, promoting reaction between substrates. enzyme substrates active site of enzyme enzyme 1 Substrates enter active site in a specific orientation. 2 Substrates and active site change shape, promoting reaction between substrates. substrates active site of enzyme enzyme 1 Substrates enter active site in a specific orientation. Figure: 05-08 Title: The cycle of enzyme–substrate interactions. Caption: