amino acids and proteins introduction

1 Amino proteins and nucleic acids INTRODUCTION Amino acids, as the name suggests are compounds which contain both an amino group (—NH 2 ) and a carboxyl group (—COOH) in their molecules. In principle, the amino group can be linked to any carbon atom of the chain. Depending upon the position of amino group i.e. α-, b-, g- etc. on the carbon chain w.r.t. the carboxyl group they are classified as α-, b-, g- etc. amino acids respectively. Out of these, α-amino acids i.e. NH2 group in linked to the carbon atom next to be — COOH group, i.e. α-carbon) are the most important because they are constituents of proteins which are very important biomolecules. The general formula of a - ainino acids is Twenty six different α-amino acids have been isolated by the hydrolysis of various proteins. Out of these 20 amino acids occur in almost all proteins while the remaining 6 are found in special tissues. These amino acids differ from one another in the nature of the side chain groups R. Therefore, properties of side chain groups R determine the properties of amino acids and the properties of proteins they constitute. In this unit, we will first describe the chemistry of α-amino acids, then we will discuss as to how these α-amino acids combine to form peptides and proteins. This will be followed by structure elucidation of peptides and proteins at different levels. Finally, we will discuss some of the important aspects of the chemistry of another important class of biomolecules called nucleic acids. NOMENCLATURE OF α-AMINO ACIDS Although amino acids can be named by the IUPAC system, they are generally known by their common names. Their common names generally end in the suffix ‘ine’. Further for sake of simplcity, each amino acid has been given a standard abbreviation or a code which usually consists of the first three letters of the common name. For example, STRUCTURE OFAMINO ACIDS α-Amino acids are generally represented as compounds containing a basic amino group and an acidic carboxyl group as shown in the general formula (I). However, in actual practice, they neutralize each other involving the transfer of a proton from the carboxyl group to the amino group within the molecule. As a result, amino acids largely exist as dipolar ions (II). The dipolar structure is commonly only known as internal salt or zwitterion. PDF Creator - PDF4Free v3.0 http://www.pdf4free.com

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Page 1: Amino Acids and Proteins Introduction

Amino proteins and nucleic acidsINTRODUCTIONAmino acids, as the name suggests are

compounds which contain both an amino group(—NH2) and a carboxyl group (—COOH) in theirmolecules. In principle, the amino group can belinked to any carbon atom of the chain. Dependingupon the position of amino group i.e. α-, b-, g-etc. on the carbon chain w.r.t. the carboxyl groupthey are classified as α-, b-, g- etc. amino acidsrespectively. Out of these, α-amino acids i.e. NH2group in linked to the carbon atom next to be —COOH group, i.e. α-carbon) are the most importantbecause they are constituents of proteins whichare very important biomolecules. The generalformula of a - ainino acids is

Twenty six different α-amino acids have beenisolated by the hydrolysis of various proteins.

Out of these 20 amino acids occur in almostall proteins while the remaining 6 are found inspecial tissues. These amino acids differ from oneanother in the nature of the side chain groups R.Therefore, properties of side chain groups Rdetermine the properties of amino acids and theproperties of proteins they constitute.

In this unit, we will first describe thechemistry of α-amino acids, then we will discussas to how these α-amino acids combine to formpeptides and proteins. This will be followed bystructure elucidation of peptides and proteins atdifferent levels. Finally, we will discuss some ofthe important aspects of the chemistry of anotherimportant class of biomolecules called nucleic acids.

NOMENCLATURE OFα-AMINOACIDSAlthough amino acids can be named by the

IUPAC system, they are generally known by theircommon names. Their common names generallyend in the suffix ‘ine’. Further for sake of simplcity,

each amino acid has been given a standardabbreviation or a code which usually consists ofthe first three letters of the common name. Forexample,

STRUCTURE OFAMINOACIDSα-Amino acids are generally represented as

compounds containing a basic amino group and anacidic carboxyl group as shown in the generalformula (I). However, in actual practice, theyneutralize each other involving the transfer of aproton from the carboxyl group to the amino groupwithin the molecule.As a result, amino acids largelyexist as dipolar ions (II).

The dipolar structure is commonly only knownas internal salt or zwitterion.

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