Amino Acidsand

DipeptidesCH2H

H

N C C

OH

O

H

CO OH

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

Polymer: large molecules consisting of large numbers of repeating units connected by covalent bonds

Monomer: a small molecule that may become chemically bonded to other monomers to form a polymer

amino acid = monomer

polypeptide = polymer

H

H

N C C

OH

O

H

R

amino group carboxyl group

R group

General structure of an amino acid

(basic) (acidic)

Different amino acids have different R groups

Their different properties depend on their R groups

Hydrophobic (‘Water-hating’) R groups

CH3H

H

N C C

OH

O

Halanine

CH2H

H

N C C

OH

O

Hphenylalanine (aromatic)

Hydrophillic (‘Water-loving’) R groups

CH2H

H

N C C

OH

O

H

SH

cysteine

CH2H

H

N C C

OH

O

H

OH

serine

CH2H

H

N C C

OH

O

H

CO NH2

asparagine (basic) aspartic acid (acidic)

CH2H

H

N C C

OH

O

H

CO OH

First isolated from asparagus juice!

You do NOT need to know their names!

There are 20 amino acids naturally incorporated into proteins

AlanineArginineAsparagineAspartic acidCysteineGlutamic acidGlutamine

Glycine HistidineIsoleucineLeucineLysineMethioninePhenylalanine

ProlineSerine ThreonineTryptophanTyrosineValine

Other amino acids do exist…

CH2H

H

N C C

OH

O

H

O

II

II

Thyroxine:used in the human body as a hormone to regulate metabolic rate

…but are not normally found in proteins

Humans can synthesis some amino acids by altering other amino acids, however…

…some amino acids cannot be synthesised and are therefore needed in the diet.

These are the essential amino acids

ArginineHistidineIsoleucineLeucine

LysineMethioninePhenylalanine

ThreonineTryptophanValine

Phenylketonuria or Maple Syrup Urine Disease

Patients lack the enzyme phenylalanine hydroxylase – needed to dispose of the amino acid phenylalanine properly

Penylalanine rapidly builds up in the blood stream

- it converted to unusual metabolites which give the patient’s urine a characteristic smell

- it also rapidly causes brain damage!

Treatment: A diet low in phelylalanine

No meat, fish, poultry, eggs, cheese, milk, beans, or peas

Formation of a dipeptide: carboxyl group of one amino acid reacts with amino group of second amino acid

H2Owater

molecule formed

H

H

N C C

OH

O

H

R2H

H

N C C

OH

O

H

R1

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

peptide linkage

a dipeptide

H

H

N C C

OH

O

H

R1 H

H

N C C

OH

O

H

R2

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

H2O

Formation of a dipeptide produces a molecule of water, therefore…

…this is a condensation reaction

2 amino acids dipeptide + water

H

H

N C C

OH

O

H

R1 H

H

N C C

OH

O

H

R2

H

H

N C C

O

H

R1 H

N C C

OH

O

H

R2

H2O

Splitting a dipeptide to form two amino acids consumes one molecule of water, therefore…

…this is a hydrolysis reaction

dipeptide + water 2 amino acids

Tripeptide: three amino acids linked together

Oligopeptide: a short chain of a few amino acids

Polypeptide: a chain of many amino acids

A protein may consist of one or more

polypeptide chains

Structure of haemoglobin – a protein consisting of four

polypeptides