amino acid to be hydrophilic (water-loving) or hydrophobic (lipid-loving)—having a major effect on the ability of the amino acid to interact with other amino acids. They can add to the charge on the amino acid and can help to create the three-dimensional shapes of proteins. You need to know that, aside from the simple amino acid glycine, the molecule will be chiral. Chiral means that there can be enantiomers, which in biochemistry are referred to as L-enantiomers and D-enantiomers (for left-sided and dextro- or right-sided enantiomers). Chemists use the same structural characteristics as glyceraldehyde to identify D-amino acids and L-amino acids because it structurally resembles amino acids. Figure 77 shows the difference between D-amino acids and L-amino acids:
Figure 77.
Nearly all amino acids are found in L-form except for a few amino acids seen in bacteria and in some antibiotics.
CARBOHYDRATES All carbohydrates have carbon, hydrogen, and oxygen atoms in them and nothing else. Examples include fiber, glycogen, and starch (which are large molecules) as well as sugars, such as glucose (a simple monosaccharide) and sucrose (a disaccharide). According to organic chemistry, carbohydrates can be described as polyhydroxy aldehydes, shown in figure 78:
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