FBICH 410 1st Edition Lecture 6Outline of Last Lecture - Amino Acids at varying pHs- Titration Curves- Unique CharacteristicsOutline 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 isoleucineo Beta carbon- D,L alloisoleucine- In biological systems mostly see pure isoleucine (not so much allo)- Chirality of Lifeo Biosynthetic process produce pure stereoisomerso Chemical processes generally produce racemic mixtureo Most active bio. Compounds are chiral where only 1 enantiomer imparts biological activity Thalidomide- originally used to treat morning sickness but was found tocause 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 regiono Only Phe, Tyr, Trp absorb UV bc of aromaticityo Absorbance at 280nm is good diagnostic device for proteins- Peptide bondo 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 Co Peptide bonds are stable- prolonged exposure to strong acid/atrong base at elevated temps are required to hydrolyzeo Peptide bond has 2 resonance structureso Partial (40%) double bond character and is consequently rigido Unchrage but polar (N partially +, O partially -)o Linus puling- described peptide bono Peptide bond is planar due to double bond character 6 atoms are always planaro Individual AA are called AA residues once incorporated into peptideo AA residue named by dropping ine and adding yl, except if it is the last residue in the chaino Charge characteristics of polypeptide- have multiple ionizable groups which affect their overall structure and chemical propertieso pKa of free carboxyl 3.5o pKa of free amino is 8.5o if Protonated pH<Pkao if deprotonated pH>pkao Must be able to determine net charge, at what pH is it drawn, pI, and titration curve of polypeptideo 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
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