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TOPIC 5: AMINO ACIDS AND PROTEINS Proteins Based on function proteins fall into 9 major classes: Table 3-1 Enzymes serving as catalysts tat greatly increase the rates of the thousands of chemical reactions Structural proteins provide support and shape to the cells and organelles, giving their characteristic and appearance Motility proteins play key roles in the contraction and movement of cells and intracellular structures Regulatory proteins are responsible for control and coordination of cellular functions Transport Proteins are involved in the movement of other substances into, out of, and within the cell Hormonal proteins mediate communication between cells in distant parts of an organism Receptor proteins enable cells to respond to chemical stimuli from their environment Defensive proteins provide protection against disease Storage proteins serve as reservoirs of amino acids There are mono-functional or bi-functional proteins which play one main function or play two distinct functions The Monomers Are Amino Acids Proteins are linear polymers of amino acids Only 20 different amino acids are used in proteins synthesis No 2 proteins have the same amino acids sequence!! This is the GENERIC FORM of an amino acid Amino acids have an asymmetric carbon atom and therefore exist in two stereoisomeric forms, D- and L-amino acid Only L-amino acid occur in proteins Amino acids depend on the chemical nature of their R-group, which are UNIQUE! Figure 3-2: 9 amino acids have a non-polar R-group and are hydrophobic (no oxygen or nitrogen), they tend to be located in the interior portion of the molecule as a polypeptide folds into its 3D shape
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11 amino acids are hydrophilic , with R-groups that are either distinctly polar or actually charged. They tend to cluster on the surface of proteins and interact with water. The Polymers Are Polypeptides and Proteins The creation of a linear polymer involves a process called condensation (dehydration) reactions . The covalent bond between a carboxyl group and an amino group is called a peptide bond (amide bond) Amino acid chain formations have intrinsic directionality , amino group ( N- terminus ) at one end and a carboxyl group ( C-terminus ) at the other end Peptide bonds are more complex because they need energy to activate the incoming amino acid and link it to transfer RNA and information
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This note was uploaded on 06/17/2008 for the course BIO 1140 taught by Professor Fenwick during the Winter '07 term at University of Ottawa.

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