Upload
naoko
View
49
Download
0
Embed Size (px)
DESCRIPTION
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 - PowerPoint PPT Presentation
Citation preview
Amino Acids, Peptides, ProteinsFunctions of proteins:
EnzymesTransport and StorageMotion, muscle contractionHormonesMechanical supportImmune protection (Antibodies)Generate and transmit nerve impulsesControl growth and differentiationLens protein in eyeFeathersSpider websHornsMilk proteinsAntibioticsMushroom poison …..
Luciferin, luciferase Hemoglobin
Amino AcidsGeneral structure
carbon, side chain (R group)
Amino Acids
Amino Acids
Amino Acids
Amino Acids
Amino Acids
Amino Acids
Nonpolar, aliphatic R group Glycine Alanine Proline Valine Leucine Isoleucine Methionine
Aromatic R groups Phenylalanine Tyrosine Tryptophan
Polar, uncharged R groups Serine Threonine Cysteine Asparagine Glutamine
Positively charge R groups Lysine Histidine Arginine
Negatively charged R groups Aspartate Glutamate
Amino Acid Abbreviations
Gly G Ala A Pro P Val V Leu L Ile I Met M
Phe F Tyr Y Trp W
Ser S Thr T Cys C Asn N Gln Q
Lys K His H Arg R
Asp D Glu E
Amino Acids
Amino AcidsAdditional properties of Amino AcidsNumbering of R group carbons
CH2
+NH3
CH COO-CH2 CH2 CH2
+NH3
Aromatic side chains absorb UV light
Disulfide bond formation with cysteine
oxidation
reduction
Trp 280 nmTyr 280 nmPhe 260 nmPeptide bond 210-214 nm
Amino AcidsNonpolar, aliphatic R group
Gly, Ala, Pro, Val, Leu, Ile, Met
Gly - no steric hindrance Pro - hinders backbone flexibility
hydrophobic core of soluble proteinsfound in transbilayer part of membrane proteins
Aromatic R groupsPhe, Tyr, Trp
hydrophobic, StackingTyr/Trp - H-bonding
Tyr - site of phosphorylation
Polar, uncharged R groupsSer, 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 groupsLys, His, Arg
His - pKa close to neutrality (catalysis); ligand for metal ions (Zn2+, Fe2+)
Negatively charged R groupsAsp, Glu
General acids/bases in catalysis (lysozyme)Chelate divalent metal ions (Mg, Ca, Mn, Zn)
Uncommon Amino Acids
collagen
myosin
prothrombin
elastin
Amino AcidsOptical Activity of Amino AcidsFor all AA except glycine the 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 AcidsOptical Activity of Amino Acids1 Chiral center = ___ stereoisomers
Stereoisomer found in proteins =
Amino acids act as acids and bases“zwitterion”amphoteric
Base = proton acceptor, electron pair donorAcid = proton donor, electron pair acceptor
Amino acid titration Curve
pK1 = a carboxyl grouppK2 = a amino groupisoelectric 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
2 buffer regions
Chemical environment influences pKa
Titration Curve of Histidine
Histidine R group has pKa = 6.0No 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 bondPolypeptide - many AA joined together by peptide bond (M.W.<10,000)Protein - macromolecule with one or more polypeptide chains
condensation
PeptidesIonization
Biologically active Peptides & Polypeptides
Dipeptide (Nutrasweet)
Other small peptidesOxytocin (9 aa) - stimulates uterine contractions Bradykinin (9 aa) - inhibits tissue inflammationAmanitin - mushroom poison PolypeptidesInsulin - pancreatic hormone, needed for sugar metabolism, 2 polypeptide chains (30 aa and 21 aa)Glucagon - pancreatic hormone, opposes action of insulin (29 aa) Corticotropin - anterior pituitary gland hormone, stimulates adrenal cortex (39 aa)
Proteins contain other prosthetic groups
Protein Structure