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Topic 4.8

AMINO ACIDS

Structure
AcidBase Properties
Condensation Reactions
Proteins






















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STRUCTURE OF AMINO ACIDS

Amino acids are molecules containing an amine group and a carboxylic acid group. Naturally
occurring amino acids have the following general formula:






There is a central carbon atom attached to a hydrogen, a carboxylic acid group, an amine group
and an alkyl group. Amino acids are…

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In high pH, therefore, amino acids exist in anionic form:






ii) reaction with acids

Amino acids react with strong acids such as hydrochloric acid:






In low pH, therefore, amino acids exist in cationic form:





iii) reaction with itself

Since amino acids have a proton donating group and a proton accepting…

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In the solid state, therefore, amino acids are ionic. This explains why they are solids with a high
melting point.

iv) summary

Amino acids can exist in molecular form, in cationic form, in anionic form or in Zwitterion form
depending on the environment:






in neutral solution in alkaline solution in…

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The resulting molecule is called a dipeptide.

Dipeptides can also be formed by the condensation of two different amino acids. In this case
two different molecules can be formed:






or






Since the resulting dipeptides also have both amine groups and carboxylic acid groups, they can
undergo further condensation reactions, eventually…

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PROTEINS

Proteins are naturally occurring polyamides formed by the condensation of many amino acid
molecules under carefully controlled conditions around the DNA backbone.

i) structure

The sequence of amino acids in a protein is known as the primary structure of the protein. It
varies from protein to protein, depending on…

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The peptide link in proteins is the same as the peptide link in Nsubstituted amides. As a result it
can be broken by heating in strong acid or strong alkali.

Proteins can thus be broken down into their constituent amino acids by heating in strong acid or
strong alkali in…

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Type of reaction Mechanism

1. acidbase reactions of amino acids

a) with acids
reagents: HCl
conditions: room temperature
equation: RCH(NH2)COOH + HCl RCH(NH3+Cl)COOH

b) with alkalis
reagents: NaOH
conditions: room temperature
equation: RCH(NH2)COOH + NaOH RCH(NH2)COONa+ + H2O

2. condensation reactions of amino acids

conditions: DNA
equation: n RCH(NH2)COOH H(NHCRHCO)nOH…

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