Amino Acids, Peptides, Proteins. Functions of proteins: Enzymes. Transport and
Storage. Motion, muscle contraction. Hormones. Mechanical support. Immune ...
Amino Acids, Peptides, Proteins Functions of proteins: Enzymes Transport and Storage Motion, muscle contraction Hormones Mechanical support Immune protection (Antibodies) Generate and transmit nerve impulses Control growth and differentiation Lens protein in eye Feathers Spider webs Horns Milk proteins Antibiotics Mushroom poison …..
Luciferin, luciferase
Hemoglobin
Amino Acids General structure α carbon, side chain (R group)
Amino Acids
Amino Acids
Amino Acids
Amino Acids
Amino Acids
Amino Acids Amino Acid
Abbreviations
Nonpolar, aliphatic R group Glycine Alanine Proline Valine Leucine Isoleucine Methionine
Gly Ala Pro Val Leu Ile Met
G A P V L I M
Aromatic R groups Phenylalanine Tyrosine Tryptophan
Phe Tyr Trp
F Y W
Polar, uncharged R groups Serine Threonine Cysteine Asparagine Glutamine
Ser Thr Cys Asn Gln
S T C N Q
Positively charge R groups Lysine Histidine Arginine
Lys His Arg
K H R
Negatively charged R groups Aspartate Glutamate
Asp Glu
D E
Amino Acids
Amino Acids Additional properties of Amino Acids Numbering of R group carbons ε 6
CH2
δ 5
CH2
γ 4
CH2
β 3
CH2
+NH 3
α 2
CH
1
COO-
+NH 3
Aromatic side chains absorb UV light
Trp 280 nm Tyr 280 nm Phe 260 nm Peptide bond 210-214 nm
Disulfide bond formation with cysteine
oxidation
reduction
Amino Acids Nonpolar, aliphatic R group Gly, Ala, Pro, Val, Leu, Ile, Met Gly - no steric hindrance Pro - hinders backbone flexibility hydrophobic core of soluble proteins found in transbilayer part of membrane proteins
Aromatic R groups Phe, Tyr, Trp hydrophobic, Stacking Tyr/Trp - H-bonding Tyr - site of phosphorylation
Polar, uncharged R groups Ser, Thr, Cys, Asn, Gln Ser/Thr - H-bonding; phosphorylated, glycosylated; enzyme active sites Cys - disulfide bonds; enzyme active sites; metal ion binding Asn/Gln - very polar, H-bonding
Positively charge R groups Lys, His, Arg His - pKa close to neutrality (catalysis); ligand for metal ions (Zn2+, Fe2+)
Negatively charged R groups Asp, Glu General acids/bases in catalysis (lysozyme) Chelate divalent metal ions (Mg, Ca, Mn, Zn)
Uncommon Amino Acids prothrombin collagen
elastin myosin
Amino Acids Optical Activity of Amino Acids For all AA except glycine the α carbon is bonded to 4 different groups: Carboxyl, amino, hydrogen, and R group (in Gly, R group is hydrogen) Chiral center = ___________________
All AA except Gly
Gly
Amino Acids Optical Activity of Amino Acids 1 Chiral center = ___ stereoisomers
Stereoisomer found in proteins =
Amino acids act as acids and bases “zwitterion” amphoteric
Base = proton acceptor, electron pair donor Acid = proton donor, electron pair acceptor
Amino acid titration Curve
2 buffer regions
pK1 = a carboxyl group pK2 = a amino group isoelectric point (pI)- pH where there is an equal amount of (+) and (-) charges (overall charge of zero) isoelectric point (pI) for glycine is at pH = 5.97 pI = (pK1 + pK2)/2
Chemical environment influences pKa
Titration Curve of Histidine
Histidine R group has pKa = 6.0 No other AA side chain has a pKa near neutral pH So Histidine is really the only AA that can be: an effective buffer at physiological pH (7.0)
Peptides and Proteins Peptide - two amino acids joined covalently by a peptide bond Polypeptide - many AA joined together by peptide bond (M.W.
