F BICH 410 1st Edition Lecture 6 Outline of Last Lecture Amino Acids at varying pHs Titration Curves Unique Characteristics Outline of Current Lecture Alpha C generally described by Fisher Convention L Amino Acids AA predominate in nature R clockwise S counterclockwise L amino group to left D amino group to right All L AA are S except Cys which is R bc of side chain 2 AA have more than one stereocenter Ile Thr o There fore 4 possible structures Problem w DL system is how to distinguish between 2 stereocenters o Alpha carbon D L isoleucine o Beta carbon D L alloisoleucine In biological systems mostly see pure isoleucine not so much allo Chirality of Life o Biosynthetic process produce pure stereoisomers o Chemical processes generally produce racemic mixture o Most active bio Compounds are chiral where only 1 enantiomer imparts biological activity Thalidomide originally used to treat morning sickness but was found to cause awful birthdefects No used to treat multiple myeloma and leprosy Possible uses HIV ulcers inflammatory disease sucha s lupus and rheumatoid arthritis and cancer Spectroscopic Properties all AA absorb IR region o Only Phe Tyr Trp absorb UV bc of aromaticity o Absorbance at 280nm is good diagnostic device for proteins Peptide bond o Dipepdie 22 AA condense ie lose H20 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Polypeptide chains are described by starting at the N terminus and proceeding to C o Peptide bonds are stable prolonged exposure to strong acid atrong base at elevated temps are required to hydrolyze o Peptide bond has 2 resonance structures o Partial 40 double bond character and is consequently rigid o Unchrage but polar N partially O partially o Linus puling described peptide bon o Peptide bond is planar due to double bond character 6 atoms are always planar o Individual AA are called AA residues once incorporated into peptide o AA residue named by dropping ine and adding yl except if it is the last residue in the chain o Charge characteristics of polypeptide have multiple ionizable groups which affect their overall structure and chemical properties o pKa of free carboxyl 3 5 o pKa of free amino is 8 5 o if Protonated pH Pka o if deprotonated pH pka o Must be able to determine net charge at what pH is it drawn pI and titration curve of polypeptide o Size of proteins many proteins have more than 1 polypeptide chain Subunits different polypeptide chains Proteins w more than 1 subunt called oligomers Each unique subunit identified by different greek letter Average formula weight of AA is 110 Daltons
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