Lippincott’s Illustrated Reviews: Biochemistry is the long-established, first-and-best resource for the essentials of biochemistry. Students rely on this text to help them quickly review, assimilate, and integrate large amounts of critical and complex information. For more than two decades, faculty and students have praised LIR Biochemistry’s matchless illustrations that make concepts come to life. Get fully prepared for coursework and board exams with these hallmark features from Lippincott’s Illustrated Reviews:

Lippincott’s Illustrated Reviews Biochemistry


Amino Acids

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 calcium phosphate crystals, acting like the steel cables in reinforced concrete. In the bloodstream, proteins, such as hemoglobin and plasma albumin, shuttle molecules essential to life, whereas immunoglobulins fight infectious bacteria and viruses. In short, proteins display an incredible diversity of functions, yet all share the common structural feature of being linear polymers of amino acids. This chapter describes the properties of amino acids. Chapter 2 explores how these simple building blocks are joined to form proteins that have unique three-dimensional structures, making them capable of performing specific biologic functions.

Bioenergetics and Oxidative Phosphorylation

Bioenergetics describes the transfer and utilization of energy in biologic systems. It makes use of a few basic ideas from the field of thermo -dynamics, particularly the concept of free energy. Changes in free energy (ΔG) provide a measure of the energetic feasibility of a chemical reaction and can, therefore, allow prediction of whether a reaction or process can take place. Bioenergetics concerns only the initial and final energy states of reaction components, not the mechanism or how much time is needed for the chemical change to take place. In short, bio -energetics predicts if a process is possible, whereas kinetics measures how fast the reaction occurs (see p. 54). 

Metabolism of Dietary Lipids

Lipids are a heterogeneous group of water-insoluble (hydrophobic) organic molecules that can be extracted from tissues by nonpolar  solvents (Figure 15.1). Because of their insolubility in aqueous solutions, body lipids are generally found compartmentalized, as in the case of membrane-associated lipids or droplets of triacylglycerol in white adipocytes, or transported in plasma in association with protein, as in lipoprotein particles (see p. 227), or on albumin. Lipids are a major source of energy for the body, and they also provide the hydrophobic bar-rier that permits partitioning of the aqueous contents of cells and subcel-lular structures. Lipids serve additional functions in the body, for example, some fat-soluble vitamins have regulatory or coenzyme functions, and the prosta glandins and steroid hormones play major roles in the control of the body’s homeostasis. Not surprisingly, deficiencies or imbalances of lipid metabolism can lead to some of the major clinical problems encoun-tered by physicians, suh as atherosclerosis and obesity.

Amino Acids: Disposal of Nitrogen

Unlike fats and carbohydrates, amino acids are not stored by the body, that is, no protein exists whose sole function is to maintain a supply of amino acids for future use. Therefore, amino acids must be obtained from the diet, synthesized de novo, or produced from normal protein degradation. Any amino acids in excess of the biosynthetic needs of the cell are rapidly degraded. The first phase of catabolism involves the removal of the α-amino groups (usually by transamination and subse-quent oxidative deamination), forming ammonia and the corresponding α-keto acid—the “carbon skeletons” of amino acids. A portion of the free ammonia is excreted in the urine, but most is used in the synthesis of urea (Figure 19.1), which is quantitatively the most important route for disposing of nitrogen from the body. In the second phase of amino acid catabolism, described in Chapter 20, the carbon skeletons of the α-ketoacids are converted to common intermediates of energy produc-ing, metabolic pathways. These compounds can be metabolized to CO2 and water, glucose, fatty acids, or ketone bodies by the central path-ways of metabolism described in Chapters 8–13, and 16.

Metabolic Effects of Insulin and Glucagon

Four major organs play a dominant role in fuel metabolism: liver, adi-pose, muscle, and brain. These tissues contain unique sets of enzymes, such that each organ is specialized for the storage, use, or generation of specific fuels. These tissues do not function in isolation, but rather form part of a network in which one tissue may provide sub-strates to another, or process compounds produced by other organs. Communication between tissues is mediated by the nervous system, by the availability of circulating substrates, and by variation in the lev-els of plasma hormones (Figure 23.1). The integration of energy metabolism is controlled primarily by the actions of two peptide hor-mones: insulin and glucagon, with the catecholamines epinephrine and norepinephrine playing a supporting role. Changes in the circulating levels of these hormones allow the body to store energy when food is available in abundance, or to make stored energy available, for exam-ple, during “survival crises,” such as famine, severe injury, and “fight-or-flight” situations. This chapter describes the structure, secretion, and metabolic effects of the two hormones that most profoundly affect energy metabolism.

DNA Structure, Replication, and Repair

Nucleic acids are required for the storage and expression of genetic information. There are two chemically distinct types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA, see Chapter 30). DNA, the repository of genetic information, is present not only in chromosomes in the nucleus of eukaryotic organisms, but also in mitochondria and the chloroplasts of plants. Prokaryotic cells, which lack nuclei, have a single chromosome, but may also contain nonchromosomal DNA in the form of plasmids. The genetic informa-tion found in DNA is copied and transmitted to daughter cells through DNA replication. The DNA contained in a fertilized egg encodes the information that directs the development of an organism. This devel-opment may involve the production of billions of cells. Each cell is specialized, expressing only those functions that are required for it to perform its role in maintaining the organism. Therefore, DNA must be able to not only replicate precisely each time a cell divides, but also to have the information that it contains be selectively expressed. Transcription (RNA synthesis) is the first stage in the expression of genetic information (see Chapter 30). Next, the code contained in the nucleotide sequence of messenger RNA molecules is translated  (protein synthesis, see Chapter 31), thus completing gene expres-sion. The regulation of gene expression is discussed in Chapter 32.

  



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