Notes for 10/26/07 Molecular structure of proteins Overview: The nucleotide sequence of mRNA specifies the amino acid sequence of a protein, or more accurately, a polypeptide. An amino acid consists of a central carbon atom, an amino group, a carboxyl group, and a side chain, or R group. Twenty different amino acids are used to make proteins. They differ only in the nature of the R group. Based on their physical properties, amino acids can be subdivided into four types: acidic, basic, neutral-nonpolar (hydrophobic), and neutral-polar (hydrophilic). In a polypeptide, amino acids are joined by peptide bonds. The amino acid sequence determines the overall structure of a protein. A protein’s structure, in turn, determines its activity or function. A mutation that changes a single amino acid in a polypeptide can have a drastic effect on the activity of a protein. The recessive genetic disease sickle cell anemia, which is caused by a mutation in the β-globin gene, is a good example of this. Terms:
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