FBICH 410 1st Edition Lecture 5Outline of Last Lecture - Standard Amino Acids- Nonstandard Amino acidsOutline of Current Lecture - Should be able to identify parent Amino acid (AA) of non-standard amino acid- Not all amino acids are found in proteins- some found with non-protein roleso Ie neurotransmitters, chemical messengerso Tyrosine parent of dopaminehistidine parent of histamine- Ionizable groups in AAo All AA have at least 2 acid-base groups ie alpha carboxyl, alpha amino, those with ionizable side chain have 3o no net charge=zwitteriono have to know pKA of all AA with ionizable side chaino alpha COOH pKa= 2.2 alpha NH3 pKA=9.5- Nonpolar AA has no ionizable side chain so have just 2 pka- Polar AA have ionizable side chain, therefore most know the R group PKAo Arginine 12.5o Cysteine 8.0o Serine 13o Glutamic acid 4.3o Histidine 6.0o Lysine 10.5o Threonine 13o Tyrosine 10.0- Ph>PKA deprotonated - polar soln less acidic, low [H], deprotonated predominate- PH< pKA protonated + polar soln acidic, high [H] so protonated predominates- Structure varies w/ PH o at low PH all ionizable groups are protonated, cationico at mid ph zwitterion dominates – no net chargeo at high ph ionizable groups are deprotonated- anionic [H removed]- Ionizable form 2 dissociable forms 3 structures- Must be able to draw amino acids at specific PHThese 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 pH<pKa protonated pH>pKa deprotonated- Titration Curves- 3 pKA 3 dissociable protons and 4 ionic forms- Ionization equilibria- titration curve from lowest (fully protonated) to highest pH (fully deprotonated)- Isoelectric point- pH at which molecule carries no charge known as pI- Calculating pI: list all pKA in ascending order, calc net charge for ph range that bracketseach pka value, identify 2 pkas that when titrated result in net charge from +1>0>-1, use 2 pkas to calculate pI pI= ½(pki+pkj)- pI of His (2.2, 6, 9.5) pH<2.2<pH<6<pH<9.5<pH+2 +1 0 -1Pi= ½(6+9.5)= 7.75- Unique Characteristicso Gly- non chiral, too flexibleo Ile + Thr- 2 chiral centerso Pro- cyclic (not primary amino), rigid not flexibleo Cys- 2 can oxidize and form disulfide bond- does ox-red rxno Asn + Gln- amides forms of Asp and
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