matriculation chemistry ( amino acids ) part 1

8/14/2019 Matriculation Chemistry ( Amino Acids ) part 1

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Chapter 20 : Amino Acids and Proteins

Amino acidAmino acid: a compound that containsboth an amino group, -NH2 and acarboxyl group, -COOH

-amino acid:-amino acid: an amino acid in which

the amino group is on the carbonadjacent to the carboxyl group

CH3CH2 C COOH

H

NH2

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1

20.1 : Introduction 20.2 : Chemical Properties

NH2 C COOH

H

CH2CH3


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Name Structure

Glycine

Gly

AlanineAla

ValineVal

H CH

NH2

COOH

H3C CH

NH2

COOH

HC CH

NH2

COOH

CH3

CH3

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name Structure

Leucine

Leu

IsoleucineIle

PhenylalaninePhe

CHCH2

CH3

CH3

CH

NH2

COOH

CH

NH2

COOHCH3CH2CH

CH3

CH2 CH

NH2

COOH

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name Structure

Threonine

Thr

CysteineCys

MethionineMet

CH2 CH2

CH2NH

C

COOH

H

HO CH2 CH

NH2

COO

H

CH3 C

H

OH

CH

NH2

COOH

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name Structure

Tryptophan

Trp

ProlinePro

SerineSer

CH2 CH2

CH2NH

C

COOH

H

HO CH2 CH

NH2

COOH

O

NH2NH

OH

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name StructureThreonineThr

CysteineCys

MethionineMet

CH3 C

H

OH

CH

NH2

COOH

HS CH

NH2

COOHCH2

CH

NH2

COOHCH3 S CH2CH2

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name Structure

Tyrosine

Tyr

AsparagineAsn

GlutamineGln

NH2CCH2CH COOH

O NH2

NH2CCH2CH2CHCOOH O NH2

CH

NH2

COOHCH2HO

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name StructureAsparticacid

Asp

Glutamicacid

GluLysineLys

HOOCCH2CH2CHCOOH

NH2

HOOCCH2CHCOOH

NH2

H2NCH2CH2CH2CH2CH COOH

NH2

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Name StructureArginineArg

HistidineHis

H2NCNH(CH2)3CHCOOH

NH NH2

HCC=CH2CH COOH N NH NH2

CH

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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H C COOH

H

NH2

i)

ethanoic acid2 1

2-amino

H C COOH

CH3

NH2

ii)

2 1

3

propanoic acid2-amino

H C COOH

CH2OH

NH2

iii)

2 1

3

propanoic acid

2-amino-3-hydroxy

IUPAC Name

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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pentanoic acid2,5-diamino

hexanedioic acid2-amino

2 1

3 4 5

H C COOH

CH2CH

2CH

2COOH

NH2

v)

H C COOH

CH2CH2CH2NH2

NH2

iv)

2 1

3 4 5 6

IUPAC Name

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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Amino acids can undergo aninternal acid-base reaction, in which aproton is transferred from thecarboxyl (-COOH) to the amino group(-NH2) to form dipolar ion calledzwitterion.

H C COOH

CH2CH2CH3

NH2

(neutral)

H C COO

CH2CH

2CH

3

NH3

-

+

(dipolar ion @zwitterion)

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1


Zwitterion


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In general, zwitterion is electricallyneutral and exists at specific pH

Isoelectric Point (pI)

This particular pH is called isoelectricpoints

Each amino acid has its specific pIExample:

Amino Acid Structure pI

Glycine(Gly)

6.1H CH

NH2

COOH

Lysine

(Lys)

9.7

Asparticacid(Asp)

2.9HOOCCH2CHCOOH

NH

2

H2N(CH2)4CH COOHNH2

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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InAcidic

The cation, H3N+ CH2 COOHpredominates (Amino acids as base)

InBasic

The anion, H2N CH2 COO-

predominates (Amino acids as acid)InpI

The zwitterion, H3N+CH2COO-predominates (Amino acids as

amphoteric)Gly (pI = 6.1)

at pH = 6.1

NH2CH2COOH

-+NH3CH2COO

-NH2CH2COO

at pH < 6.1 at pH > 6.1

+NH3CH2COOH

-amino acid

20 amino acids

Naming

Zwitterion

Isoelectric point

Structures in:

Acidic

Basic

pI

20.1



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a) Reaction with HCl

R C NH2

COOH

R'

+ HCl R C NH3Cl

COOH

R'_+

Example:

20.2 : Chemical Properties

Reactions ofNH2 group:

Peptide bond

HCl

NaOH

HNO2

ROH

Reactions of-COOH group:

20.2

H C NH2COOH

CH2CH3

+ HCl

20.1 : Introduction

H C NH3ClCOOH

CH2CH3_+

Importance


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b) With Nitrous Acid (HNO2)



Peptide bond

HCl

NaOH

HNO2

ROH


20.2

20.1 : Introduction

elimination of N2(g)

R C

COOH

R'

+

carbocationH2O

2-hydroxy

carboxylic acid

Cl-

+

halocarboxylic

acid

- H+

Alkenoic

acid

Observation: Bubblingof gas (N2)

Importance

R C NH2

COOH

R'

R C N N

COOH

R'+

diazonium ion

NaNO2 / HCl

-5 to 0 oC


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Example:H C NH2

COOH

CH3

H C N N

COOH

CH3+

diazonium ion

NaNO2 / HCl

elimination of N2(g)

H C

COOH

CH3+

carbocation

H2O

H C OH

COOH

CH3Cl-+

H C Cl

COOH

CH3

- H+

H C

COOH

CH2


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c) Reaction with NaOH

Example:



Peptide bond

HCl

NaOH

HNO2

ROH


20.2

20.1 : Introduction

R C NH2

COOH

R'

+ NaOH R C NH2

COO Na

R'

_ +

H C NH2

COOH

CH2CH3

+ NaOH H C NH2

COO Na

CH2CH3

_+

Importance


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d) Reaction with ROH + HCl (catalyst)

Example:



Peptide bond

HCl

NaOH

HNO2

ROH


20.2

20.1 : Introduction

R C NH2

COOH

R'

+ R''OH + H2OR C NH2

COOR''

R'

H C NH2

COOH

CH2CH3

+ CH3OH

HCl

+ H2OR C NH2

COOR''

R'

Importance


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Peptidesareamino acid polymersin which the individual amino acidunits, are linked together by amidebonds, orpeptide bonds

Peptide Bond2amino acids react together, H2Ois eliminated.This is condensation reaction.



Peptide bond

HCl

NaOH

HNO2

ROH


20.2

2 amino acids form dipeptide3 amino acids form tripeptide15 30amino acids form oligopeptide> 30amino acids form polypeptide

20.1 : Introduction

Importance


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Formation of dipeptide bond:

+

+

H2O

H2N CH2 C OH H N C COOH

H CH3

H

H2N CH2 C N C COOH

H CH3

H

O

O

amide bond /

peptide bond

A dipeptide

Notes:

N-terminal (with free NH2) is

always written on the left and C-terminal (with free COOH) at theright side



Peptide bond

HCl

NaOH

HNO2

ROH


20.2

Importance


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Formation of tripeptide bond:

Write the structural formula of tripeptide with the followingsequence Gly-Ala-Tyr :

H2N CH2 C OH H N C COOH

H CH3

HOH N C COOH

H H

CH2 OH

Gly Ala Tyr

H2N CH2 C N C C

H CH3

HO

N C COOH

H

CH2 OHO

H

A tripeptide


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Importance of amino acids :



Peptide bond

Importance

HCl

NaOH

HNO2

ROH


20.2 Human beings can synthesize about half

of the amino acids needed to makeproteins.

Other amino acids, called the essentialessentialamino acidsamino acids, must be provided in the diet.

The ten essential amino acids are :

arginine (Arg) valine (val) methionine (Met)threonine (Thr) leucine (Leu) phenylalanine (Phe)histidine (His) isoleucine (Ile) lysine (Lys)trypthophan (Trp)


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Importance of proteins :



Peptide bond

HCl

NaOH

HNO2

ROH


20.2 Proteins are the most abundant organic

molecules in animals, playing importantroles in all aspects of cell structure and

function. Examples of protein functions :

Class of protein Examples Functions

structural protein collagen, keratin tendons, skin

hair, nails

enzymes DNA polymerase repair DNA

transport protein hemoglobin transport O2Importance

matriculation chemistry ( amino acids ) part 1

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