ENERGY AND THE CELL

5.10 Cells transform energy as they perform work Cells are small units, a chemical factory, housing thousands of chemical reactions. Energy may be used or released during these reactions. © 2012 Pearson Education, Inc.

5.10 Cells transform energy as they perform work Energy is the capacity to cause change or to perform work. There are two kinds of energy. 1.Kinetic energy is the energy of motion Transfer motion to other matter (legs pushing bike pedals) Heat/thermal energy: random motion of molecules Light energy: photosynthesis © 2012 Pearson Education, Inc.

5.10 Cells transform energy as they perform work 1.Potential energy is energy that matter possesses as a result of its location or structure. Bike at the top of a hill Water behind a dam Chemical energy: used to power cells

5.10 Cells transform energy as they perform work Thermodynamics: the study of energy transformations First law of thermodynamics: energy can be transferred or transformed, but it cannot be created or destroyed. – Batteries transform stored energy into electric energy – Plants: light is transformed into chemical energy (photosynthesis) – Cellular respiration: chemical energy is converted to a form the cell can use (ATP) to do work

5.10 Cells transform energy as they perform work The second law of thermodynamics: energy conversions create entropy. – A measure of disorder During energy transformations some energy is converted to heat which disordered energy and unable to do work

Figure 5.10 Fuel Energy conversion Waste products Gasoline Oxygen Glucose     Heat energy Combustion Kinetic energy of movement Energy conversion in a car Energy conversion in a cell Energy for cellular work Cellular respiration ATP Heat energy Carbon dioxide Water

5.11 Chemical reactions either release or store energy Chemical reactions either – release energy (exergonic reactions) Burning sugar such as a marshmallow (fast) Cellular respiration (slow) – require an input of energy and store energy (endergonic reactions). Products of the reaction contain more energy than the reactants – photosynthesis © 2012 Pearson Education, Inc.

Figure 5.11A Reactants Energy Products Amount of energy released Potential energy of molecules

Figure 5.11B Reactants Energy Products Amount of energy required Potential energy of molecules

5.11 Chemical reactions either release or store energy The total of an organism’s chemical reactions is called metabolism. A metabolic pathway – builds a complex molecule or – breaks down a complex molecule into simpler compounds. © 2012 Pearson Education, Inc.

5.11 Chemical reactions either release or store energy Energy coupling uses the – energy released from exergonic reactions to drive – essential endergonic reactions, – usually using ATP molecules. © 2012 Pearson Education, Inc.

ATP, adenosine triphosphate, powers nearly all forms of cellular work ATP drives cellular work by coupling exergonic and endergonic reactions © 2012 Pearson Education, Inc.

5.12 ATP drives cellular work by coupling exergonic and endergonic reactions Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. Most cellular work depends on ATP energizing molecules by phosphorylating them. © 2012 Pearson Education, Inc.

Figure 5.12A_s1 Adenine P P P Phosphate group ATP:Adenosine Triphosphate Ribose

Figure 5.12A_s2 ADP: Adenosine Diphosphate P P P Energy H2OH2O Hydrolysis Ribose Adenine P P P Phosphate group ATP:Adenosine Triphosphate

Figure 5.12B ATP ADP P P P P P P P P P Chemical work Mechanical workTransport work Reactants Motor protein Solute Membrane protein Product Molecule formed Protein filament moved Solute transported

5.12 ATP drives cellular work by coupling exergonic and endergonic reactions ATP is a renewable source of energy for the cell.. © 2012 Pearson Education, Inc.

Figure 5.12C Energy from exergonic reactions Energy for endergonic reactions ATP ADP P

HOW ENZYMES FUNCTION © 2012 Pearson Education, Inc.

5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers Although biological molecules possess much potential energy, it is not released spontaneously. – An energy barrier must be overcome before a chemical reaction can begin. – This energy is called the activation energy (E A ). © 2012 Pearson Education, Inc.

Figure 5.13A Activation energy barrier Reactant Products Without enzyme With enzyme Reactant Products Enzyme Activation energy barrier reduced by enzyme Energy

Figure 5.13Q Reactants Products Energy Progress of the reaction a b c

5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers Enzymes – function as biological catalysts by lowering the E A needed for a reaction to begin, – increase the rate of a reaction without being consumed by the reaction, and – are usually proteins, although some RNA molecules can function as enzymes. Hydrolysis of sucrose © 2012 Pearson Education, Inc.

Figure 5.14_s Products are released Fructose Glucose Enzyme (sucrase) Active site Enzyme available with empty active site Substrate (sucrose) Substrate binds to enzyme with induced fit Substrate is converted to products H2OH2O

5.14 A specific enzyme catalyzes each cellular reaction For every enzyme, there are optimal conditions under which it is most effective. Environment affects protein shape Temperature affects molecular motion. – Most human enzymes work best at 35–40ºC. The optimal pH for most enzymes is near neutrality. © 2012 Pearson Education, Inc.

5.15 Enzyme inhibitors can regulate enzyme activity in a cell A chemical that interferes with an enzyme’s activity is called an inhibitor. Competitive inhibitors (many drugs and poisons) – block substrates from entering the active site and – reduce an enzyme’s productivity. Noncompetitive inhibitors – bind to the enzyme somewhere other than the active site, – change the shape of the active site, and – prevent the substrate from binding. © 2012 Pearson Education, Inc.

Figure 5.15A Substrate Enzyme Allosteric site Active site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

5.15 Enzyme inhibitors can regulate enzyme activity in a cell Enzyme inhibitors are important in regulating cell metabolism.. © 2012 Pearson Education, Inc.

5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors Many beneficial drugs act as enzyme inhibitors, including – Ibuprofen, inhibiting the production of prostaglandins, – some antidepressants, – protease inhibitors used to fight HIV. Enzyme inhibitors have also been developed as pesticides and deadly poisons for chemical warfare. © 2012 Pearson Education, Inc.