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!"#$%&'()*+(#,-./(#0-123( $4/56-.23(7(&.89,62( ( ( !"#"$%&'()$*%#+,'(-(.+/&/*+,%&(01"2+34$5( 6%#+,"(!/$75#38+(92+41( CHAPTER 21: Amino Acids, Proteins, Enzymes Learning Objectives: ! >1"(;?(,/22/#'(#%4@$%&&5(/,,@$$+#*(A2+#/(A,+<3( ! 34"$"/,1"2+34$5(( ! %,+<BC%3"(,1"2+34$5( ! D"EF<"3( ! G/$2%F/#( ! H(-(0(4"$2+#%&3( ! D$/4"+#3( ! D$+2%$5'(9",/#<%$5'(>"$F%$5'(I@%4"$#%$5(34$@,4@$"( ! J5<$/&53+3(%#<(<"#%4@$%F/#( ! =#752"3( ! 0%4%&53+3( ! K#1+C+4/$3( ! L52/*"#3( CH 21 Homework: End of Chapter problems: 32, 36, 38, 42, 48, 50, 52, 62, 64, 68, 70, 74, 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( 77, 81, 93, 94( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;( Amino Acids Definition All amino acids contain two functional groups—an amino group (NH2) and a carboxyl group (COOH). Amino acids differ in the R group bonded to the ! carbon 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Amino Acids M( At isoelectric pH • The isoelectric point for amino acids is about 6, this is the pH at which the amino acid exists as a neutral molecule • The pKa of the amine group is usually about 9-11 • The pKa of the carboxylic acid group is usually about 2-3 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( N( Amino Acids Acid/Base Chemistry 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Amino Acids O( Stereochemistry • Carbohydrates: naturally occurring isomer is the Disomer (OH group on right in a Fischer projection) • Amino Acids: most naturally occurring isomers are the Lisomer (NH3 group on the left in a Fischer projection) 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( P( The 20 common & naturally occurring amino acids in humans. Essential Amino Acids: Isoleucine (Ile) Leucine (Leu) Methionine (Met) Phenylalanine (Phe) Threonine (Thr) Tryptophan (Trp) Valine (Val) Arginine (Arg) Histidine (His) Lysine (Lys) Q( Peptides Definition • Peptides and proteins are formed when amino acids are joined together by amide bonds. • A dipeptide has two amino acids joined together by one amide bond. • The amide bond is called a peptide bond. • Polypeptides have many amino acids, while proteins have more than 40 amino acids. 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( R( Peptides Amide Bond Formation 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Peptides S( Amide Bond Formation 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( T?( Peptides N & C Terminal Amino Acids • The amino acid with the free –NH3+ group is the N-terminal amino acid and is written on the left. • The amino acid with the free –COO" group is the C-terminal amino acid and is written on the right. 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Peptides/ Protein TT( Insulin Gly-Ile-Val-Glu-Gln-Cys-Cys-Thr-Ser-Ile-Cys-Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys-R Phe-Val-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala-Leu-Tyr-Leu-Val-Cys-GlyGlu-Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Thr-R’ 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( T;( Proteins Primary Structure The primary structure of a protein is the sequence of amino acids joined together by peptide bonds. 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Proteins TM( Secondary Structure • The secondary structure is the 3D arrangement of localized regions of a protein. • These regions arise due to hydrogen bonding between the N—H group of one amide with the C#O group of another. 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( TN( Proteins Secondary Structure 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Proteins TO( Tertiary Structure The tertiary structure is the 3D shape adopted by the entire peptide chain: • Maximize Hydrogen bonding with water (hydrophilic) • Stabilize non-polar sidechains by london dispersion forces (hydrophobic) • Polar functional groups H-bond with each other • Charged sidechains attracted through electrostatic interactions • Disulfide bonds form 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( TP( Proteins Tertiary Structure 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Proteins TQ( Quaternary Structure The quaternary structure of the protein is the shape adopted when two or more folded poly-peptide chains come together into one complex. Ex: Potassium Channel: 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( TR( Proteins Quaternary Structure Hemoglobin 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Proteins TS( Quaternary Structure Hemoglobin 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;?( Proteins 1°, 2°, 3°, 4° Structure 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Proteins ;T( Peptide Hydrolysis Protein hydrolysis involves breaking the peptide bonds by treatment with aqueous acid, base, or certain enzymes: Pepsin (gastric juices), Trypsin and Chymotrypsin (intestines) 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;;( Proteins Peptide Denaturation Denaturation is the process of altering the shape of a protein without breaking the amide bonds that form the primary structure: heat, acid, base, or agitation 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( Enzymes ;M( Definition Enzymes are proteins that serve as biological catalysts for reactions in all living organisms. • They increase the rate of a reaction (106 to 1012 times faster), but are unchanged themselves. • Enzymes are very specific; each enzyme catalyzes a certain reaction or type of reaction only. • The names of most enzymes end with the suffix -ase like peptidase, lipase, and hydrolase • A cofactor is a metal ion or an organic molecule needed for an enzyme-catalyzed reaction to occur. 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;N( Enzymes Function 1UEVBB&"%W+#*C+/:#"4B"#752"3:142( Enzymes ;O( Conformational Changes Upon Binding 1UEVBBE&%#4,"&&C+/&/*5:2%34"$3:*$8$%X:/$*B142&BD&%#4Y0"&&Y.+/,1"2+34$5YA#<YZ"4%C/&+32T[D$/4"+#3YA#<Y=#752"3:142( ;P( Enzymes Inhibition ;Q( 1UEVBB/:\@+7&"4:,/2B+B]^_]R8<]_`)aTaLC=<b*5AY2:XE*( Enzymes Zymogens 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;R( Superoxide Dismutase Enzymes H N O OH2 OH OAsp FeIII O2- OH OAsp NHis Asp 156 O NHis O2- H+ NHis OAsp FeII NHis NHis OH2 HOOH H+ 2H+ OAsp FeII NHis NHis His 160 N His 73 NH NH OH2 NHis FeIII N His 26 N O2 NHis Fe NHis NHis O2- O2NHis * O2- hydrogen bonds to residues in secondary coordination sphere, positioning it near Fe(II), 92+41'(6%#+,"(!/$75#38+:(!"#"$%&'()$*%#+,'( -(.+/&/*+,%&(01"2+34$5(;#<(=<:( ;S(