Carbohydrates, Nucleic Acids, and Lipids

The anabolic branch then is targeted to the different macromolecules proteins, carbohydrates, nucleic acids, and lipids and possibly further detailing to ceU wall carbohydrates and starch as storage material. These are formed with rates fMacro of which the cell consists so that the mass balance can be set up as... 

The biological molecules that make up living cells, organs, systems, and the environment can be divided into four types proteins, carbohydrates, nucleic acids, and lipids. Most of these molecules are simple structures covalently bonded to similar molecules, but some can reach incredible sizes in molecular terms. They are called macromolecules. Figure 18.1 shows an example of a macromolecule S-carotene (the yellow color in carrots). 

The molecules of biological organisms fall into four groups proteins, carbohydrates, nucleic acids, and lipids (nonpolymaic materials soluble in organic solvents, such as fats and oils). Proteins and nucleic acids, and many carbohydrates, are polymers. In this chapter, we will limit our discussion to proteins and nucleic acids. Proteins are the basic constituents of living organisms we discuss these substances in the next section. Nucleic acids are important in the synthesis of proteins we discuss these in the final section of the chapter. 

Chemists and biochemists And it convenient to divide the principal organic substances present m cells into four mam groups carbohydrates proteins nucleic acids and lipids Structural differences separate carbo hydrates from proteins and both of these are structurally distinct from nucleic acids Lipids on the other hand are characterized by a physical property their solubility m nonpolar solvents rather than by their structure In this chapter we have examined lipid molecules that share a common biosynthetic origin m that all their carbons are derived from acetic acid (acetate) The form m which acetate occurs m many of these processes is a thioester called acetyl coenzyme A... 

Of the four major classes of biochemicals (carbohydrates, proteins, nucleic acids and lipids), experiments have shown that the first three classes could have arisen through prebiotic chemistry. Although the biosynthesis of many natural products can be traced back to acetate (e.g. fatty acids, terpenes and polyketide biosynthesis) or amino acids (e.g. alkaloid biosynthesis), there are many whose biosynthetic origins are either obscure or result from a complex combination of pathways (Fig. 2). 

A "minireview" of methods, with emphasis on proteins, follows. Additional procedures having to do primarily with carbohydrates, nucleic acids, or lipids are given in Chapters 4,5, and 8, respectively. 

Let us take an overview of carbohydrates, one of the four major classes of biotnolecules along with proteins, nucleic acids, and lipids. Carbohydrates are aldehydes or ketones with multiple hydroxyl groups. 

The most basic sorting of isotopes occurs in the distribution of carbon among nucleic acids, proteins, carbohydrates, and lipids, the major classes of compounds present within most cells. The most important pathways of carbon flow are indicated schematically in Figure 6. In autotrophs, these lead from carbohydrates (the direct products of carbon fixation) to proteins, nucleic acids, and lipids. Biomass—the organic material that... 

Emphasis will be placed on recent structural and conformational studies of relatively large molecules, particularly those of biochemical importance. The 1 3 C nmr of carbohydrates, nucleic acids and their constituents, proteins and their residues, lipids and macromolecular model systems will be discussed in detail and attempts will be made to cover the literature exhaustively. This somewhat arbitrary selection is dictated by the availability of recent summaries on 13C spectroscopic measurements of steroids (Gray,... 

Arts. Undecomposed plant or animal matter is crushed into small particles or powder using a blender or other mechanical device and then a nonpolar or low-polarity solvent such as diethyl ether, hexane, benzene, or carbon tetrachloride is added. Lipids dissolve in the nonpolar solvent while other compounds (proteins, carbohydrates, nucleic acids, and inorganics) do not. The solution is filtered from the insoluble matter and then the solvent evaporated to yield the lipids. 

WE HAVE NOW studied the structures and typical reactions of the major types of organic functional groups. Further, we have examined the structures of carbohydrates, amino acids and proteins, nucleic acids, and lipids. Now let us apply this background to the study of the organic chemistry of metabolism. In this chapter, we study three key metabolic pathways glycolysis, the citric acid cycle, and the /3-oxidation of fatty acids. The first is a pathway by which glucose is converted to pyruvate and then to acetyl coenzyme A. The second is a pathway by which the hydrocarbon chains of fatty acids are degraded, two carbons at a time, to acetyl coenzyme A. The third is the pathway by which the carbon skeletons of carbohydrates, fatty acids, and proteins are oxidized to carbon dioxide. 

Chapters 17—20 present an introduction to the organic chemistry of carbohydrates, amino acids and proteins, nucleic acids, and lipids. Chapter 21, The Organic Chemistry of Metabolism, demonstrates how the chemistry developed to this point can be applied to an understanding of three major metabolic pathways—glycolysis, the /3-oxidation of fatty acids, and the citric acid cycle. 

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