Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Energy is defined as the capacity to do work –Synthesis (making macromolecules) –Movement: muscle contraction, cilia moving –Creating ionic gradients (Na + outside, K + inside) –Bioluminescence ENERGY AND THE CELL
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Kinetic energy is energy that is actually doing work Potential energy is stored energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings First law of Thermodynamics –Energy cannot be created nor destroyed –However, energy can be changed from one form to another Two laws govern energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Some common energy transformations
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Second law of Thermodynamics –Energy transformations are not 100% efficient; some energy is always lost in a transformation. –Energy conversions increase disorder, or entropy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
There are two types of chemical reactions: –Endergonic reactions absorb energy and yield products rich in potential energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
In cellular respiration, some energy is stored in ATP molecules ATP powers nearly all forms of cellular work ATP shuttles chemical energy within the cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction releases energy. This energy can be used for cellular work Phosphate groups Adenine Ribose Adenosine triphosphate Hydrolysis Adenosine diphosphate (ADP) Energy
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The ATP cycle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Review An exergonic reaction releases energy. It occurs “spontaneously.” An endergonic reaction consumes energy. It requires an input of energy to occur. An endergonic reaction can be driven by an exergonic reaction if the two are COUPLED (joined together).
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Reactions can be coupled: an exergonic reaction can “push” an endergonic reaction forward.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Reactions can be coupled: an exergonic reaction can “push” an endergonic reaction forward.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
What are enzymes? From the Greek “in yeast” Proteins (mostly) Catalysts –increase the rate of a reaction –are not changed in the reaction (can be reused) They physically bind with their substrate to produce product.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings For a chemical reaction to begin, reactants must absorb some energy –This energy is called the energy of activation (E A ) –This represents the energy barrier that prevents molecules from breaking down spontaneously Enzymes speed up the cell’s chemical reactions by lowering energy barriers HOW ENZYMES WORK
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A protein catalyst called an enzyme can decrease the energy barrier E A barrier Reactants 1Products2 Enzyme Figure 5.5A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings E A with enzyme Figure 5.5B Reactants Products E A without enzyme Net change in energy
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes are selective, or specific. –Selectivity is based on the shape and charge on the active site of the protein enzyme. –Only some reactants (substrates) fit well enough. A specific enzyme catalyzes each cellular reaction
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme (sucrase) Active site Substrate (sucrose) Enzyme available with empty active site Substrate binds to enzyme with induced fit Substrate is converted to products 4 Products are released GlucoseFructose How an enzyme works The enzyme is unchanged and can repeat the process Figure 5.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sir Alexander Fleming Lysozyme: a polysaccharidase
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzyme activity is influenced by –pH –temperature Some enzymes require nonprotein cofactors, organic molecules called coenzymes NAD FAD The cellular environment affects enzyme activity
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Inhibitors interfere with enzymes –A competitive inhibitor takes the place of a substrate in the active site –A noncompetitive inhibitor alters an enzyme’s function by changing its shape Enzyme inhibitors block enzyme action Substrate Enzyme Active site NORMAL BINDING OF SUBSTRATE Competitive inhibitor Noncompetitive inhibitor ENZYME INHIBITION Figure 5.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Certain pesticides are toxic to insects because they inhibit enzymes in the nervous system (acetylcholinesterase inhibitors) Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria –Penicillin inhibits an enzyme that bacteria use in making cell walls Connection: Some pesticides and antibiotics inhibit enzymes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts carry out photosynthesis, using solar energy to produce glucose and oxygen from carbon dioxide and water Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP Chloroplasts and mitochondria transform energy and make it available for cellular work
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The exergonic burning of the sun Drives (is coupled to) the endergonic synthesis of glucose. The exergonic burning of glucose Drives (is coupled to) the endergonic synthesis of ATP. The exergonic hydrolysis of ATP is used to do work. Figure 5.21 Sunlight energy Chloroplasts, site of photosynthesis CO 2 + H 2 O Glucose + O 2 Mitochondria sites of cellular respiration (for cellular work) Heat energy