Chapter 1: Amino Acids

 Overview Proteins are the most abundant and functionally diverse molecules in living systems. Virtually every life process depends on this class of molecules. For example, enzymes and polypeptide hormones direct and regulate metabolism in the body, whereas contractile proteins in muscle permit movement. In bone, the protein collagen forms a framework for the deposition of […]

Chapter 2: Structure of Proteins

Overview The 20 amino acids commonly found in proteins are joined together by peptide bonds. The linear sequence of the linked amino acids contains the information necessary to generate a protein molecule with a unique three-dimensional shape. The complexity of protein structure is best analyzed by considering the molecule in terms of four organizational levels, […]

Chapter 3: Globular Proteins

Overview The previous chapter described the types of secondary and tertiary structures that are the bricks-and-mortar of protein architecture. By arranging these fundamental structural elements in different combinations, widely diverse proteins can be constructed that are capable of various specialized functions. This chapter examines the relationship between structure and function for the clinically important globular […]

Chapter 4: Fibrous Proteins

Overview Collagen and elastin are examples of common, well-characterized fibrous proteins of the extracellular matrix that serve structural functions in the body. For example, collagen and elastin are found as components of skin, connective tissue, blood vessel walls, and sclera and cornea of the eye. Each fibrous protein exhibits special mechanical properties, resulting from its […]

Chapter 5: Enzymes

Overview Virtually all reactions in the body are mediated by enzymes, which are protein catalysts that increase the rate of reactions without being changed in the overall process. Among the many biologic reactions that are energetically possible, enzymes selectively channel reactants (called substrates) into useful pathways. Enzymes thus direct all metabolic events. This chapter examines […]

Chapter 6: Bioenergetics and Oxidative Phosphorylation

Overview Bioenergetics describes the transfer and utilization of energy in biologic systems. It makes use of a few basic ideas from the field of thermodynamics, particularly the concept of free energy. Changes in free energy (?G) provide a measure of the energetic feasibility of a chemical reaction and can, therefore, allow prediction of whether a […]

Chapter 7: Introduction to Carbohydrates

Overview Carbohydrates are the most abundant organic molecules in nature. They have a wide range of functions, including providing a significant fraction of the dietary calories for most organisms, acting as a storage form of energy in the body, and serving as cell membrane components that mediate some forms of intercellular communication. Carbohydrates also serve […]

Chapter 8: Glycolysis

Introduction to Metabolism In Chapter 5, individual enzymic reactions were analyzed in an effort to explain the mechanisms of catalysis. However, in cells, these reactions rarely occur in isolation, but rather are organized into multistep sequences called pathways, such as that of glycolysis (Figure 8.1). In a pathway, the product of one reaction serves as […]

Chapter 9: Tricarboxylic Acid Cycle

Overview The tricarboxylic acid cycle (TCA cycle, also called the Krebs cycle or the citric acid cycle) plays several roles in metabolism. It is the final pathway where the oxidative metabolism of carbohydrates, amino acids, and fatty acids converge, their carbon skeletons being converted to CO2. This oxidation provides energy for the production of the […]

Chapter 10: Gluconeogenesis

Overview Some tissues, such as the brain, red blood cells, kidney medulla, lens and cornea of the eye, testes, and exercising muscle, require a continuous supply of glucose as a metabolic fuel. Liver glycogen, an essential postprandial source of glucose, can meet these needs for only 10–18 hours in the absence of dietary intake of […]