5 Weak bonds—such as hydrogen bonds (Figure 3 Weak bonds—such as hydrogen bonds (Figure 3.2), van der Waals forces, and hydrophobic interactions—also affect macromolecular structure, but through more subtle atomic interactions.
12 An Overview of Macromolecules and Water as the Solvent of Life
13 Understanding the relative composition of a bacterial cell (Table 3 Understanding the relative composition of a bacterial cell (Table 3.2) helps us to understand the metabolic needs of the organism.
15 The bacterial cell is about 70% water, with over one-half of the dry portion being made up of protein and one-quarter being made up of nucleic acids.
16 Proteins (Figure 3. 3a) are polymers of monomers called amino acids Proteins (Figure 3.3a) are polymers of monomers called amino acids. Nucleic acids (Figure 3.3b) are polymers of nucleotides and are found in the cell in two forms, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
20 The cohesive and polar properties of water promote chemical interaction and help shape macromolecules into functional units.
21 PART II Noninformational Molecules Polysaccharides
22 Sugars combine into long polymers called polysaccharides.
23 The relatively simple yet eloquent structure of the polysaccharides (Figure 3.4) and their derivatives (Figure 3.5) makes them the most abundant natural polymer on Earth and allows them to be used for metabolism, as a component of information transfer molecules (Figure 3.8), and for cellular structure.
29 Glycosidic bonds (Figure 3 Glycosidic bonds (Figure 3.6) combine monomeric units (monosaccharides) into polymers (polysaccharides), all with a carbon-water (carbohydrate) chemical composition approaching (CH2O)n.
32 The two different orientations of the glycosidic bonds that link sugar residues impart different properties to the resultant molecules. Polysaccharides can also contain other molecules such as proteins or lipids, forming complex polysaccharides.
33 LipidsLipids are amphipathic—they have both hydrophilic and hydrophobic components. This property makes them ideal structural components for cytoplasmic membranes.
34 Simple lipids (triglycerides) are composed of a glycerol molecule with fatty acids (Figure 3.7) covalently linked in ester (Bacteria) or ether (Archaea) bonds.
41 The nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are macromolecules composed of monomers called nucleotides. Therefore, DNA and RNA are polynucleotides. Without a phosphate, a base bonded to its sugar is referred to as a nucleoside.
42 All nucleotides have a phosphate group and a five-carbon sugar, with the sugar being ribose (–OH at carbon 2) in RNA or deoxyribose (–H at carbon 2) in DNA (Figure 3.10).
53 The fourth bond can be one of 21 common side groups, which may be ionic, polar, or nonpolar (Figure 3.12b). It is the heterogeneity of these side groups that defines the properties of a peptide or protein.
60 These different structural forms can greatly affect metabolism; for example, whereas sugars are typically d enantiomer, amino acids typically exist in the l form.
61 Proteins: Primary and Secondary Structure The sequence of covalently linked amino acids in a polypeptide is the primary structure. When many amino acids are covalently linked via peptide bonds, they form a polypeptide.
62 Secondary structure results from hydrogen bonding that produces an -helix ("corkscrew") or -sheet ("washboard") formation, or domain (Figure 3.16). Proteins may have an assortment of either or both domains.
65 Proteins: Higher Order Structure and Denaturation The polar, ionic, and nonpolar properties of amino acid side "R" chains cause regions of attraction and repulsion in the amino acid chain, thus creating the folding of the polypeptide (i.e., tertiary structure) (Figure 3.17).
71 It is this final orientation and folding that dictate the usefulness of a protein as a catalyst (enzyme) or its structural integrity in the cell. Destruction of the folded structure by chemicals or environmental conditions is called denaturation (Figure 3.19).