D. Cellular Respiration
Learning Objectives for this Section
As mentioned previously, to grow, function, and reproduce, cells must:
1) synthesize new cellular components such as cell walls, cell membranes, nucleic acids, ribosomes, proteins, flagella, etc., and;
2) harvest energy and convert it into a form that is usable to do cellular work.
Catabolism (def) refers to the exergonic (def) process by which energy released by the breakdown of organic compounds such as glucose can be used to synthesize ATP, the form of energy required to do cellular work. Anabolism (def) is the endergonic (def) process that uses the energy stored in ATP to synthesize the building blocks of the macromolecules that make up the cell. As can be seen, these two metabolic processes are closely linked. Another factor that links catabolic and anabolic pathways is the generation of precursor metabolites. Precursor metabolites (def) are intermediate molecules in catabolic and anabolic pathways that can be either oxidized to generate ATP or can be used to synthesize macromolecular subunits such as amino acids, lipids, and nucleotides.
In this section we will concentrate primarily on harvesting energy and converting it to energy stored in ATP through the process of cellular respiration, but we will also look at some of the key precursor metabolites that are produced during this process.
Cellular respiration (def) is the process cells use to convert the energy in the chemical bonds of nutrients to ATP energy. Depending on the organism, cellular respiration can be aerobic, anaerobic, or both. Aerobic (def) respiration is an exergonic pathway that requires molecular oxygen (O2). Anaerobic (def) exergonic pathways do not require oxygen and include anaerobic respiration and fermentation. We will now look at these three pathways.
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