CHAPTER 8 An Introduction to Metabolism CH 8 Learning Objectives 1 Identify the first two laws of thermodynamics and explain how they relate to biological systems 2 Explain what is meant by change in free energy and relate it to the following spontaneous reactions capacity to do work stability and exergonic and endergonic reactions 3 Use examples to illustrate the coupling of ATP hydrolysis to endergonic reactions 4 Explain how enzymes speed up metabolic reactions 5 Describe how regulation of enzyme activity helps control metabolism I would suggest completing the crossword puzzle to help you understand the terminology and correlate how the terms relate to topics covered in this chapter How do the laws of thermodynamics relate to biological processes Energy use by living things demonstrates the 1st law of thermodynamics Energy can be transferred or transformed but not created or destroyed The conversion of energy to thermal energy released as heat by living things demonstrates the 2nd law of thermodynamics Every energy transfer or transformation increases the entropy disorder of the universe Figure 8 1b 1st and 2nd law of thermodynamics examples CONCEPT 8 1 An organism s metabolism transforms matter and energy Metabolism is the totality of an organism s chemical reactions It is an emergent property of life that arises from orderly interactions between molecules In a metabolic pathway a specific molecule is altered in a series of steps to produce a product Each step is catalyzed by a specific enzyme a macromolecule that speeds up a specific reaction Catabolic pathways release energy by breaking down complex molecules into simpler compounds EX Cellular respiration the breakdown of glucose in the presence of O2 Anabolic pathways consume energy to build complex molecules from simpler ones EX the synthesis of protein from amino acids Catabolic pathways are described as downhill reactions whereas anabolic pathways are uphill Living things use energy released from the downhill reactions of catabolic pathways to power the uphill reactions of anabolic pathways Bioenergetics is the study of how energy flows through living organisms Forms of Energy Energy the capacity to cause change can be used to do work move matter against opposing forces such as gravity and friction Energy exists in various forms Living cells must transform energy from one form to another to do the work of life Kinetic energy is energy associated with motion Moving objects perform work by imparting motion to other matter EX water gushing through a dam turns turbines Thermal energy is the kinetic energy associated with random movement of atoms or molecules Thermal energy in transfer from one object to another is called heat Light is another type of energy that can be harnessed to do work such as photosynthesis Potential energy is energy that matter possesses because of its location or structure EX water behind a dam possesses energy because of its altitude above sea level Molecules possess energy due to the arrangement of electrons in bonds between their atoms Chemical energy is potential energy available for release in a chemical reaction Complex molecules such as glucose are high in chemical energy because energy is released as they are broken down to simpler products Energy can be converted from one form to another EX chemical energy from food is used to perform the work of climbing up to a diving platform The kinetic energy of muscle movement is transformed into potential energy as the diver climbs higher above the water The potential energy is then transformed to kinetic energy as the diver falls back down to the water Figure 8 2 The Laws of Energy Transformation Thermodynamics is the study of energy transformations in a collection of matter An isolated system such as the liquid in a thermos bottle is unable to exchange energy or matter with its surroundings In an open system such as the Earth energy and matter can be transferred between the system and its surroundings Organisms are open systems they absorb energy from light or food and release heat and metabolic wastes such as CO2 to the surroundings The First Law of Thermodynamics According to the 1st law of thermodynamics the energy of the universe is constant Energy can be transferred and transformed but it CANNOT be created or destroyed The first law is also called the principle of conservation of energy The Second Law of Thermodynamics During every energy transfer or transformation some energy is converted to thermal energy and lost as heat becoming unavailable to do work According to the 2nd law of thermodynamics Every energy transfer or transformation increases the entropy of the universe Entropy is a measurement of molecular disorder or randomness Living organisms increase the disorder of their surroundings through their metabolism EX the breakdown of food releases heat and small molecules such as CO2 Processes that increase the entropy of the universe can occur spontaneously Spontaneous processes occur without energy input they can happen quickly or slowly ice melting Processes that decrease entropy are nonspontaneous they require an input of energy Biological Order and Disorder Cells create ordered structures from less organized starting materials i e amino acids form proteins Complex ordered structures are also produced from simpler starting materials at the organismal level The increase in order within living systems is balanced by the catabolic breakdown of organized forms of matter releasing heat and small molecules Energy flows into ecosystems as light exits as heat The evolution complex organisms from simpler ancestors does not violate the second law Entropy disorder may decrease in a particular system such as an organism as long as the total entropy of the system and surroundings increases CONCEPT 8 2 The free energy change of a reaction tells us whether or not the reaction occurs spontaneously Biologists follow the energy and entropy changes during chemical reactions to determine whether they require an input of energy or occur spontaneously Gibbs free energy G can be simplified and referred to as free energy Free energy is the portion of a system s energy that can do work when temperature and pressure are uniform throughout the system as in a living cell Change in free energy during a reaction is related to temperature and changes in enthalpy and entropy G H T S G change in free energy H change in enthalpy total energy S change in entropy T
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