Lecture 2 - Lecture 2 Chapter 3 Proteins polymers of amino...

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Lecture 2 Chapter 3 - Proteins – polymers of amino acids, w each amino acid residue joined to its neighbor by a specific type of covalent bond - All 20 of the common amino acids are α-amino acids – they have a carboxyl group & an amino group bonded to the same carbon atom (the α carbon) differ from each other in their side chains, or R groups, which vary in structure, size, and electric charge, & which influence the solubility of the amino acids in water - Amino & carboxyl groups of amino acids, along w the ionizable R groups of some amino acids, function as weak acids & bases – when an amino acid lacking an ionizable R group is dissolved in water at neutral pH, it exists in solution as the dipolar ion, or zwitterions, which can act as either an acid or a base - Additional carbons in an R group are commonly designated β, γ, δ, ε, and so forth, proceeding out from the α carbon - For all the common amino acids except glycine, the α carbon is bonded to 4 different groups: a carboxyl group, an amino group, an R group, and a hydrogen atom (except proline) o The α carbon atom is thus a chiral center – amino acids have 2 possible stereoisomers – since they are nonsuperposable mirror images of each other, the 2 forms represent a class of stereoisomers – the absolute configurations of simple sugars and amino acids are specified by the D, L system – for all chiral compounds, stereoisomers having a configuration related to that of L-glyceraldehyde are designated L, and stereoisomers related to D-glyceraldehyde are designated D nearly all biological compounds w a chiral center occur naturally in only 1 stereoisomeric form, either D or L – the amino acid residues in protein molecules are exclusively L stereoisomers
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Lecture 2 - Lecture 2 Chapter 3 Proteins polymers of amino...

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