A triacylglycerol can contain three different fatty acids that vary in length and level of saturation. Another critical function of lipids is the formation of membranes; all biological membranes are formed by the aggregation of lipids. As discussed later, the sulfhydryl group of cysteine plays an important role in protein structure because disulfide bonds can form between the side chains of different cysteine residues. The roles of proteins include serving as structural components of cells and tissues, acting in the transport and storage of small molecules e. Consequently, the interactions between water and the other constituents of cells are of central importance in biological chemistry.
Purines are shaded green and pyrimidines are shaded yellow. Every nucleotide is made of phosphate, a ribose or deoxyribose sugar, and a structure called a base which contains nitrogen. There is another class of polymers based on a backbone of Si and O atoms; these polymers are called A polymer based on a silicon and oxygen backbone. A Water is a polar molecule, with a slight negative charge δ - on the oxygen atom and a slight positive charge δ + on the hydrogen atoms. Unsaturated contain one or more double bonds between carbon atoms; in saturated fatty acids all of the carbon atoms are bonded to the maximum number of hydrogen atoms. D-glucose is a ringed, six-carbon sugar that exists in two configurations: alpha and beta see Figure 4.
Cellulose also functions as a structural molecule in plants and it is a major component of the plant cell wall. Disaccharides are composed of two monosacchrides linked by a glycosidic bond. Constitution and Biosynthesis of Lignin. The Si atoms have organic groups attached to them, so these polymers are still organic. Waxes are made of fatty acids and alcohols. Polysaccharides are storage forms of sugars and form structural components of the cell. Proteins have two types of well-classified, frequently occurring elements of local structure defined by a particular pattern of along the backbone: and.
The is the regular arrangement of amino acids within localized regions of the polypeptide. This is illustrated in Figure 3. In the , the two fatty acids are bound to carbon atoms in glycerol, as in triacylglycerols. The structure of the molecule can therefore be deduced from the pattern of scattered X rays the diffraction pattern. The nucleotide sequence is abbreviated to the single letter designation for the base of each nucleotide A, C, G and T or U.
The loop regions connecting the elements of are found on the surface of folded proteins, where the polar components of the peptide bonds form hydrogen bonds with water or with the polar side chains of hydrophilic amino acids. Both and are composed entirely of glucose molecules in the α configuration. Ten amino acids have nonpolar side chains that do not interact with water. The complementary strands are antiparallel recall parallel and antiparallel orientations of beta sheets in Tutorial entitled. The three components of a nucleotide the nitrogenous bases, the sugars and the phosphate group are shown in the blue frames.
Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone fatty acids or by both single and fatty acids. The side chains of two amino acids, cysteine and methionine, contain sulfur atoms. The hydroxyl group points down in alpha-D-glucose and it points up in beta-D-glucose. Triacylglycerols are commonly referred to as fats or oils, and are predominantly energy-storage molecules. The such as estrogens and are derivatives of see.
In this example, all three fatty acids are palmitate, but triacylglycerols often contain a mixture of different fatty acids. Polysaccharides are polymers of glucose Polysaccharides are long chains of repeating simple sugars. One of them, poly ethylene oxide , results not from the opening of a double bond but the opening of a ring in the monomer; the concept of bonding with other monomers, however, is the same. Because adding one monomer to another forms this polymer, polyethylene is an example of a type of polymer called addition polymers. The principal linkage is between carbon 1 of one glucose and carbon 4 of a second. Cellulose, a polysaccharide poly meaning many, and saccharide referring to sugar , is classified as a carbohydrate.
Unlike the macromolecules described previously proteins, nucleic acids and polysaccharides , lipids are not polymers of a repeating monomer. As discussed later in this chapter, such interactions of polar and nonpolar molecules with water and with each other play crucial roles in the formation of biological structures, such as cell membranes. A beam of X rays is directed at crystals of the protein to be analyzed, and the pattern of X rays that pass through the protein crystal is detected on X-ray film. The A-T base pair has two hydrogen bonds, and the G-C base pair has three. The side chains of these amino acids are and therefore tend to be located in the interior of , where they are not in contact with water. Base pairs differ in their number of hydrogen bonds.