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protein structure and function - 2

protein structure and function - 2 - 21 (Biol.Chem.410A...

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2-1 Cell and Molecular Biology (Biol. Chem. 410A) Lecture #2 Harry R. Matthews, Ph.D. September 27, 1996 Protein Structure and Function   Clinical correlations: antibody-antigen interactions sickle cell anemia Parkinson’s disease MSG Learning objectives: molecular interactions pH and electrostatic interactions amino acid building blocks of proteins summaries of amino acid properties Optional reading: Stryer 4th Ed.: Chapter 2 Alberts et al.: 3rd Ed., Chapter 2, pages 46-53, Chapter 3,  pages 90-95. on-covalent interactions are key to  understanding the behavior of biolo- gical molecules. These interactions in- clude: N electrostatic interactions hydrogen bonding hydrophobic interactions steric hindrance Van der Waals interactions In this chapter we will be concerned with  interactions between amino acids, particularly  in proteins. Changes in these interactions,  such as in the substitution of hydrophobic  valine for hydrophilic glutamic acid in sickle  cell hemoglobin, give rise to sickle cell an- emia. Even free amino acids can be critical to  body functions. For example, glutamic acid  and dopamine are important messenger mo- lecules in the brain. Too much glutamic acid  (usually eaten in the form of MSG—mono so- dium glutamate) causes “Chinese restaurant  syndrome”. Low levels of dopamine are an im- portant part of Parkinson’s disease and some  improvement can be achieved by raising the  level of dopamine in the brains of Parkinson’s  patients. Amino Acids. The properties of an amino acid are determ- ined partly by its amino (-NH 3 + ) and carboxyl  (-COO - ) groups and partly by its side-chain. In  proteins it is mainly the side-chain properties  that are important. However, many amino  acids occur free in body fluids and the analys- is of proteins usually involves breaking them  down into amino acids so the properties of the  free amino acid are important. Determination  of the concentrations of free amino acids in  urine is used as a diagnostic indicator. Figure 2-2. Molecular interactions. The  large complex protein molecule on the right is  an antibody and the protein on the left is the  antigen. In the upper panel the two molecules  are separate; in the lower panel they are to- Figure 2-1. Sickled erythrocytes.  These  deformed red blood cells cause anemia  and sickle cell crises. (Lehninger et al.,  2nd edition, fig. 7–27B, p. 187.)
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2-2 gether. The antibody binds specifically to the  antigen through non-covalent interactions.  This specific interaction is fundamental to im- munity. (From: Amit et al., 1986, Science 233,  747-753.)The most important properties of  amino acids, for our purposes, are:
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