hilic. The R groups of the amino acids determine the polarity of the complete amino acid. If a molecule is known to be Polar it has a slightly negative or positive end because one of the atoms draws more electrons than the others. Polar molecules are attracted to water because water is also polar (polar molecules have charges, and the negative charge of one attracts the positive charge of the other because opposites attract) with oxygen having a slightly negative charge and both hydrogen atoms consiting of a slightly positive charge. Therefore, polar molecules are hydrophilic (like to be affiliated with water) and nonpolar molecules are hydrophobic (hate water). See Figure 2 for a look at a polar amino acid and view Figure 3 for a nonpolar amino acid. Some amino acids are also dipolar or charged.
             Proteins take on many classifications in order to differentiate them from other proteins. Some of these classifications are determined based on their structure. One such classification is whether a protein is globular or fibrous. Hemoglobin is a globular protein. Another classification based on structure has four categories. Proteins undertake four structures in order to get to their final structure. They are primary, secondary, tertiary, and quaternary. This classification is based on whether there is a straight amino acid chain, if the polypeptide chain is coiled or in a pleated sheet (fan-like), if the coiled chain is twisted and made into a globular structure, or if two or more coiled and twisted chains are put together. The difference of proteins results in the differences in these structures. Many proteins only go through three of these steps because they don¡t mix with other globular structures. Some proteins, including hemoglobin, form quaternary structure when 2 or more polypeptide sequences come together and wrap around each other. In a hemoglobin molecule the polypeptide subunits are called globins. When four globins and four h...