Energy and MetabolismAn organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics - The totality of an organism’s chemical reactions is called metabolism.- Metabolism is an emergent property of life that arises from interactions between molecules within the orderly environment of the cell.The chemistry of life is organized into metabolic pathways.- Metabolic pathways begin with a specific molecule, which is then altered in a series of defined steps to form a specific product.- A specific enzyme catalyzes each step of the pathway.- Catabolic pathways release energy by breaking down complex molecules to simpler compounds.- A major pathway of catabolism is cellular respiration, in which the sugar glucose is broken down in the presence of oxygen to carbon dioxide and water.- Anabolic pathways consume energy to build complicated molecules from simpler compounds. They are also called biosynthetic pathways.- The synthesis of protein from amino acids is an example of anabolism.- The energy released by catabolic pathways can be stored and then used to drive anabolic pathways.- Energy is fundamental to all metabolic processes, and therefore an understanding of energy is key to understanding how the living cell works.- Bioenergetics is the study of how organisms manage their energy resources. Organisms transform energy.- Energy is the capacity to do work.- Energy exists in various forms, and cells transform energy from one type into another.- Kinetic energy is the energy associated with the relative motion of objects.- Objects in motion can perform work by imparting motion to other matter.- Photons of light can be captured and their energy harnessed to power photosynthesis in green plants.- Heat or thermal energy is kinetic energy associated with the random movement of atoms or molecules.- Potential energy is the energy that matter possesses because of its location or structure.- Chemical energy is a form of potential energy stored in molecules because of the arrangement of their atoms.- Energy can be converted from one form to another.- For example, as a boy climbs stairs to a diving platform, he is releasing chemical energy stored in his cells from the food he ate for lunch.- The kinetic energy of his muscle movement is converted into potential energy as he climbs higher.- As he dives, the potential energy is converted back to kinetic energy.- Kinetic energy is transferred to the water as he enters it.- Some energy is converted to heat due to friction.1The energy transformations of life are subject to two laws of thermodynamics.- Thermodynamics is the study of energy transformations.- In this field, the term system refers to the matter under study and the surroundings include everything outside the system.- A closed system, approximated by liquid in a thermos, is isolated from its surroundings.- In an open system, energy and matter can be transferred between the system and its surroundings.- Organisms are open systems.- They absorb energy—light or chemical energy in the form of organic molecules—and release heatand metabolic waste products such as urea or CO2 to their surroundings.- The first law of thermodynamics states that energy can be transferred and transformed, but it cannot be created or destroyed.- The first law is also known as the principle of conservation of energy.- Plants do not produce energy; they transform light energy to chemical energy.- During every transfer or transformation of energy, some energy is converted to heat, which is the energy associated with the random movement of atoms and molecules.- A system can use heat to do work only when there is a temperature difference that results in heat flowing from a warmer location to a cooler one.- If temperature is uniform, as in a living cell, heat can only be used to warm the organism.- Energy transfers and transformations make the universe more disordered due to this loss of usable energy.- Entropy is a quantity used as a measure of disorder or randomness.- The more random a collection of matter, the greater its entropy.- The second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe.- While order can increase locally, there is an unstoppable trend toward randomization of the universe.- Much of the increased entropy of the universe takes the form of increasing heat, which is the energy of random molecular motion.- In most energy transformations, ordered forms of energy are converted at least partly to heat.- Automobiles convert only 25% of the energy in gasoline into motion; the rest is lost as heat.- Living cells unavoidably convert organized forms of energy to heat.- For a process to occur on its own, without outside help in the form of energy input, it must increase the entropy of the universe.- The word spontaneous describes a process that can occur without an input of energy.- Spontaneous processes need not occur quickly.- Some spontaneous processes are instantaneous, such as an explosion. Some are very slow, such as the rusting of an old car.- Another way to state the second law of thermodynamics is for a process to occur spontaneously, it must increase the entropy of the universe.- Living systems create ordered structures from less ordered starting materials.- For example, amino acids are ordered into polypeptide chains.2- The structure of a multicellular body is organized and complex.- However, an organism also takes in organized forms of matter and energy from its surroundings and replaces them with less ordered forms.- For example, an animal consumes organic molecules as food and catabolizes them to low-energy carbon dioxide and water.- Over evolutionary time, complex organisms have evolved from simpler ones.- This increase in organization does not violate the second law of thermodynamics.- The entropy of a particular system, such as an organism, may decrease as long as the total entropy of the universe—the system plus its surroundings—increases.- Organisms are islands of low entropy in an increasingly random universe.- The evolution of biological order is perfectly consistent with the laws of thermodynamics.Free-Energy - Free energy is the portion of a system’s energy that is able to perform work when temperature andpressure is uniform throughout the system, as in a living cell.- The free energy (G) in a system is related to the total enthalpy (in biological systems, equivalent toenergy) and the entropy