rav65819_ch06_105-118

rav65819_ch06_105-118 - *104 Chapter 6 introduction Energy...

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***104 Chapter 6 Energy and Metabolism introduction LIFE CAN BE VIEWED AS A CONSTANT flow of energy, channeled by organisms to do the work of living. Each of the significant properties by which we define life—order, growth, reproduction, responsiveness, and internal regulation—requires a constant supply of energy. Both the lion and the giraffe need to eat to provide energy for a wide variety of cellular functions. Deprived of a source of energy, life stops. Therefore, a comprehensive study of life would be impossible without discussing bioenergetics, the analysis of how energy powers the activities of living systems. In this chapter, we focus on energy— what it is and how it changes during chemical reactions. 6.3 ATP: The Energy Currency of Cells n Cells store and release energy in the bonds of ATP n ATP hydrolysis drives endergonic reactions n ATP cycles continuously 6.4 Enzymes: Biological Catalysts concept outline 6.1 The Flow of Energy in Living Systems n Energy can take many forms n The Sun provides energy for living systems n Oxidation–reduction reactions transfer electrons while bonds are made or broken 6.2 The Laws of Thermodynamics and Free Energy n The Frst law states that energy cannot be created or destroyed n The second law states that some energy is lost as disorder increases n Chemical reactions can be predicted based on changes in free energy n Spontaneous chemical reactions require activation energy n An enzyme alters the activation energy of a reaction n Active sites of enzymes conform to Ft the shape of substrates n Enzymes occur in many forms n Environmental and other factors affect enzyme function 6.5 Metabolism: The Chemical Description of Cell Function n Biochemical pathways organize chemical reactions in cells n Biochemical pathways may have evolved in stepwise fashion n ±eedback inhibition regulates some biochemical pathways
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***105 6.1 The Flow of Energy in Living Systems Thermodynamics is the branch of chemistry concerned with energy changes. Cells are governed by the laws of physics and chemistry, so we must understand these laws in order to understand how cells function. Energy can take many forms Energy is defined as the capacity to do work. We think of energy as existing in two states: kinetic energy and potential energy (figure 6.1). Kinetic energy is the energy of motion. Moving objects perform work by causing other matter to move. Potential energy is stored energy. Objects that are not actively moving but have the capacity to do so possess potential energy. A boulder perched on a hilltop has gravitational potential energy; as it begins to roll downhill, some of its potential energy is converted into kinetic energy. Much of the work that living organisms carry out involves transforming potential energy into kinetic
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rav65819_ch06_105-118 - *104 Chapter 6 introduction Energy...

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