organic and biological chemistry
DESCRIPTION
Organic and Biological Chemistry . 4.8 Amides. Amides. Amide functional group. Amides. Possible under high temp for extended time to prepare amide from a carboxylic acid and an amine or ammonia (condensation) RCOOH + NH 3 RCOO – NH 4 + RCOO – NH 4 + +H 2 O. Amides. - PowerPoint PPT PresentationTRANSCRIPT
Organic and Biological Chemistry
4.8 Amides
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Amides
2
R C
H
H
N
H
C O
CH
H
R
R C
H
H
N
H
C O
CH
H
R
Amide functional group
AmidesPossible under high temp for extended
time to prepare amide from a carboxylic acid and an amine or ammonia (condensation)
RCOOH + NH3 RCOO– NH4+
RCOO– NH4+ +H2O
3
R C
O
N H
H
R C
O
N H
H
AmidesRCOOH + RNH2 RCOO–
+ RNH3+
RCOO– RNH3
+ +H2O
Amides are produced by the reactions of acid halides, acid anhydrides or esters with amines or ammonia
4
R C
O
N H
R
R C
O
N H
R
5
Lidocaine
Prilocaine
AmidesHydrolysis of amides will occur with
extended refluxing under acid or alkaline conditions
Under acid conditions the amide will hydrolyse to form the carboxylic acid and protonated amine
RCONRH + H+ + H2O RCOOH + NH3R+
Under alkaline conditions the products are the carboxylate ion and an amine
RCONRH + OH– RCOO– + NH2R6
Organic and Biological Chemistry
4.9 Proteins
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Proteins: Amino acids
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Amino acids have both an Amino and a carboxyl functional group
R group which varies giving 20 different natural amino acids
Simplest is Glycine where R= H
acid
N
H
H
C
H
R
C
O
O
H
N
H
H
C
H
R
C
O
O
H
amino General Form
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Proline Histidine
Methionine
Proteins : Amino acids
10
N
H
H
H C
H
R
C
O
O
N
H
H
H C
H
R
C
O
O+
−
Amino acids can self ionise to form a ZWITTERION by transferring a proton from the carboxyl group to the amine group
The molecule does not have an overall charge
Proteins: FormationProteins are polyamides formed when amino
acids (monomer) covalently bond with each other to form large molecules
The link between the amino acids is referred to as a peptide link or peptide bond (amide group)
The reaction is a condensation reaction which is catalysed by enzymes
Proteins are also referred to as polypeptides (long chain molecules with many peptide links)
Proteins don’t have a repeating unit as the R groups vary along the polypeptide 11
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Proteins: Types of BondingPrimary (covalent bonds) form the chainsPrimary (ionic and covalent bonds) and
secondary interactions between chains and secondary interactions within chains affect the shape of the protein
13
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Proteins: Secondary interactionsHydrogen bonding can occur between
peptide links both within a protein chain and between protein chains
Hydrogen bonding can occur between polar R groups on protein chains
Hydrogen bonds will also form between the polypeptide and water molecules
15
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ProteinsHydrogen bonding (and
other secondary interactions) within and between polypeptide chains results in each protein having a specific structure.
This structure is unique to the protein and is necessary for the protein to carry out its biological function.
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ProteinsWithin the structure of proteins are active
sites which “fit” specific molecules.If the structure of a protein is changed in any
way by the disruption of the secondary interactions then the active sites will be changed and will no longer fit the specific molecules.
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ProteinsIf this occurs the protein is said to be
denatured.Consequently the protein loses its ability to
perform its biological function. Enzymes are proteinsTheir ability to biologically catalyse reactions
is affected if their spatial arrangement is disrupted
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Proteins
Changes in pHAlters ionic bonding between NH3
+ and COO– groups
Acid: Converts ionic carboxylate ions to carboxylic acids RCOO – + H+ RCOOH
Alkali: Converts protonated amines to amine groups RNH3
+ + OH– RNH2
This disrupts bonds between side groups destabilising the protein structure.
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ProteinsTemperatureProteins work effectively within a limited
temperature range.Raising a protein to 50oC or above disrupts
secondary bonds destabilising the structure.
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