Chapter 8
- 1. Chapter 8 An Introduction to Metabolism
- 2. I. Energy: The capacity to do work. The ability to change matter Can exist in two forms: 1. Kinetic energy : Energy of motion. Energy that is actively performing work. Examples: Heat : Energy of particles in motion. Light : Energy of photons of light 2. Potential energy : Stored energy due to position or arrangement of matter. Examples: Chemical energy : Potential energy of molecules due to the arrangement of atoms. The most important type of energy for living organisms. Position : Bicycle at the top of a hill.
- 3. Kinds of Energy Electromagnetic Chemical Nuclear Light Mechanical Electrical Heat Sound
- 4. II. Energy Transformation Energy can be converted from one kind to another. Transformations are inefficient , generating heat. Examples : Light energy -------- --> Chemical energy (sugar) + Heat Chemical energy -- ---> Mechanical energy + Heat Electrical energy --- --> Light energy + Heat Chemical energy --- --> Biological work + Heat Heat is easily measured energy, because all other forms of energy can be converted to heat. From a biological standpoint, heat is a poor kind of energy which is not very useful to do work. Why? Because heat is lost to the environment.
- 5. III. All energy transformations are subject to the First and Second Laws of Thermodynamics 1. First Law of Thermodynamics : Energy can be transformed (e.g.: chemical to mechanical), but cannot be created nor destroyed. The total amount of energy in the universe is constant . Biological Consequence : Living organisms cannot create the energy they need to live. They must capture it from their environment. Sources of energy used by living organisms : Sun and chemical energy.
- 6. 2. Second Law of Thermodynamics ENERGY CONVERSIONS ARE INEFFICIENT In any energy transformation, a certain amount of energy is lost as heat. By comparison, living organisms are relatively efficient. Electrical Energy -------> ---------> 5% Light + 95% Heat Chemical Energy --> ----------------> 25% Mechanical (Gasoline) 75% Heat Chemical Energy --------> -----------> 40% ATP + 60% Heat (Glucose)
- 7. III. Laws of Thermodynamics (Cont.) 2. Second Law of Thermodynamics : Energy conversions reduce the order of the universe, because heat is dispersed into the environment. As a result, the universe inevitably tends toward a state of increased disorder or chaos ( entropy ). Entropy (S) : Measure of disorder. Disorganized, less usable energy (heat). Heat is random molecular motion, a form of entropy. Biological Consequences : Living organisms must constantly take in energy to avoid entropy (disintegration, death and decay). High quality energy is a limited resource, because usable energy, decreases over time.
- 8. IV. Chemical Reactions Either Store or Release Energy : I. Exergonic Reactions : Release free energy. Also exothermic (release heat). Products have less energy than the reactants. Example : Cellular respiration is an exergonic process: C 6 H 12 O 6 + 6 O 2 ----> 6 CO 2 + 6 H 2 O + Energy Sugar Oxygen Carbon Water Dioxide High Energy Reactants Low Energy Products
- 9. Change in Free Energy of a System: G = H - T S G is Gibb’s Free Energy or the energy available to do work. H is the total energy. T is the temperature in Kelvin. S is entropy Exergonic Reactions, G - Endergonic Reaction, G +
- 10. IV. Chemical Reactions Store or Release Energy : II. Endergonic Reactions : Require net input of free energy. Also endothermic (absorb heat). Products have more energy than the reactants. Create products that are rich in potential energy. Example : Photosynthesis is an endergonic process: 6 CO 2 + 6 H 2 O + Sunlight ----> C 6 H 12 O 6 + 6 O 2 Carbon Water Energy Sugar Oxygen Dioxide Low Energy Reactants High Energy Products
- 11. Chemical Reactions Either Store or Release Energy Endergonic Reactions Exergonic Reactions Require Energy Release Energy Higher Energy Products Lower Energy Products
- 12. Metabolism : All chemical processes that occur within a living organism. Either catabolic or anabolic reactions. I. Catabolic Reactions : Release energy ( exergonic ). Break down large molecules (proteins, polysaccharides) into their building blocks (amino acids, simple sugars). Often coupled to the endergonic synthesis of ATP. Examples : 1. Cellular respiration is a catabolic process: C 6 H 12 O 6 + 6 O 2 -------> 6 CO 2 + 6 H 2 O + Energy Sugar Oxygen Carbon dioxide Water 2. The digestion of sucrose is a catabolic process: Sucrose + Water -------> Glucose + Fructose + Energy Disaccharide Monosaccharides
- 13. Metabolism: Catabolism + Anabolism II. Anabolic Reactions : Require energy ( endergonic ). Build large molecules (proteins, polysaccharides) from their building blocks (amino acids, simple sugars). Often coupled to the exergonic breakdown or hydrolysis of ATP. Examples : 1. Photosynthesis is an anabolic process: 6 CO 2 + 6 H 2 O + Sunlight ----> C 6 H 12 O 6 + 6 O 2 Carbon Water Sugar Oxygen Dioxide 2. Synthesis of sucrose is an anabolic process: Glucose + Fructose + Energy -------> Sucrose + H 2 O Monosaccharides Disaccharide
- 15. V. ATP: Shuttles Chemical Energy in the Cell Coupled Reactions : Endergonic and exergonic reactions are often coupled to each other in living organisms. The energy released by exergonic reactions is used to fuel endergonic reactions. ATP “shuttles” energy around the cell from exergonic reactions to endergonic reactions . One cell makes and hydrolyzes about 10 million ATPs/second. Cells contain a small supply of ATP molecules (1-5 seconds ). ATP powers nearly all forms of cellular work: 1. Mechanical work : Muscle contraction, beating of flagella and cilia, cell movement, movement of organelles, cell division. 2. Transport work: Moving things in & out of cells. 3. Chemical work : All endergonic reactions.
- 16. A. Structure of ATP (Adenosine triphosphate) Adenine : Nitrogenous base. Ribose : Pentose sugar, same ribose of RNA. Three Phosphate groups: High energy bonds . B. ATP Releases Energy When Phosphates Are Removed: Phosphate bonds are rich in chemical energy and easily broken by hydrolysis : ATP + H 2 O ----> ADP + Energy + P i ADP + H 2 O ----> AMP + Energy + P i
- 17. Structure and Hydrolysis of ATP
- 18. C. Regeneration of ATP : ATP can be regenerated through dehydration synthesis : ADP + Energy + P i ----> ATP + H 2 O Phosphorylation : Transfer of a phosphate group to a molecule. Requires energy. The energy required for this endergonic reaction is obtained by trapping energy released by other exergonic reactions (E.g.: Cellular respiration).
- 19. ATP Shuttles Energy From Exergonic Reactions to Endergonic Reactions
Editor's Notes
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