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Cover Biochemistry

Aerobic Metabolism II: Electron Transport and Oxidative Phosphorylation  

This chapter analyses how the aerobic lifestyle depends on the large quantities of energy made possible by oxygen, which is also required directly or indirectly for 1000 biochemical reactions that cannot occur under anaerobic conditions. It cites research efforts which have revealed that aerobic organisms have evolved an array of mechanisms that provide protection from the toxic by-products of oxygen metabolism. Many enzymes and antioxidant molecules prevent most oxidative cell damage. The chapter describes oxygen metabolites that are now known to contribute to an array of human disorders that include cancer and heart and neurological diseases. Oxygen has several properties that, when combined, have made possible a highly favourable mechanism for extracting energy from organic molecules.

Chapter

Cover Biochemistry

Photosynthesis  

This chapter considers oxygenic photosynthesis as the most important biochemical process on earth. With a few minor exceptions, photosynthesis is the only mechanism by which an external abiotic source of energy is harnessed by the living world, and it is the source of O2, which sustains all aerobic organisms. It explains photosynthesis as the light-driven biochemical mechanism whereby CO2 is incorporated into organic molecules, such as glucose. The chapter refers to captured light energy that is used to synthesise adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH), which drive the process. The reducing power of NADPH is necessary as a strong electron donor is required to reduce the fully oxidised, low-energy carbon atoms in CO2 to the carbon units of organic molecules.

Chapter

Cover Biochemistry

Aerobic Metabolism I: The Citric Acid Cycle  

This chapter discusses modern aerobic organisms that transduce the chemical bond energy of food molecules into the bond energy of adenosine triphosphate (ATP). It examines how aerobic organisms perform this feat where oxygen is used as the terminal acceptor of the electrons extracted from food molecules. The capacity to use oxygen to oxidise nutrients, such as glucose and fatty acids, yields a substantially greater amount of energy than does fermentation. The chapter recounts the accumulation of atmospheric O2 on Earth about 2 billion years ago, when existing organisms were confronted with a serious problem: molecular oxygen forms toxic oxygen ions and peroxides called reactive oxygen species (ROS). ROS react with and damage or destroy biomolecules. Consequently, exposure to O2 acted as a severe selection pressure.