CHEM 18-1 - Ch. 18 Amino Acids and Proteins The many...

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Ch. 18 – Amino Acids and Proteins The many various functions of proteins are: 1) Enzymes - used for biological catalysis of cellular reactions 2) Structural function – provide mechanical support to large animals and provide them with their outer coverings (e.g., in collagen making up connective tissue or keratin in hair or fingernails) 3) Nutrients – serve as sources of amino acids for embryos and infants, e.g., egg albumin and casein in milk are examples 4) Protective (or Defense) – as antibodies against infectious agents (antigens) 5) Regulatory – control many aspects of cell function, like metabolism and reproduction, such as hormones (insulin, glucagon, oxytocin, vasopressin) 6) Nerve impulse transmission – at the receptors of synapses and involved in vision (rhodopsin) 7) Motion – are necessary for all forms of movement, involved in contraction of muscle tissue, through the interaction of actin and myosin 8) Transport – carry other compounds throughout body (e.g., the lipoproteins which carry cholesterol in bloodstream to and from the liver, or hemoglobin and myoglobin which serve to transport oxygen in bloodstream) Amino Acids Proteins are in all living species, from bacteria to humans we all are constructed from the same basic set of 20 amino acids, pp. 601. As the name amino acid suggests, one has an amino group (--NH 2 ) on a C attached also to a carboxyl group (namely the α C atom). Amino acids are known exclusively by their common names as the IUPAC names are difficult (you will not have to memorize them). Also attached to the α C atom is an R group, which renders the amino acid its own unique characteristics due to its size, shape, solubility, and ionization properties. The conformation and biological activity of resulting proteins are seriously affected by it. Chemists classify amino acids in 4 groups, which depend on the nature of the functional group on the side chain (at neutral pH): 1) non-polar (or hydrophobic), 2) polar but neutral, 3) negatively charged, and 4) positively charged (when these amino acids are at pH 7.0).
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Three-letter abbreviations for amino acids will be used in this class. For example, glycine is
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CHEM 18-1 - Ch. 18 Amino Acids and Proteins The many...

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