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Amino acids

Amino acids. To be able to identify the general molecular formula of amino acids. All amino acids have the same basic structure They have an amine group (NH 2 ) at one end And a carboxyl acid group (COOH) at the other end There is an R group which differs from one amino acid to another.

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Amino acids

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  1. Amino acids • To be able to identify the general molecular formula of amino acids

  2. All amino acids have the same basic structure • They have an amine group (NH2) at one end • And a carboxyl acid group (COOH) at the other end • There is an R group which differs from one amino acid to another. • For example • in glycine, the side chain is a single hydrogen atom so R = H • In alanine, the side chain is a methyl group so R = CH3

  3. H O O C R C H N H H α-amino acids General molecular formula of an amino acid: RCH(NH2)COOH Structural formula carboxylic acid group The group that determines what amino acid is amine group

  4. aspartic acid cysteine glycine asparagine histidine

  5. In each case circle the amine group, carboxylic acid group and the R group What does ‘essential’ mean? These are the essential α-amino acids. The carbon atoms and hydrogen atoms bonded to them are not shown – just the skeleton

  6. As a class make as many physical models of alanine as possible (R = CH3). Compare the models you made and try to sort them into two groups. • Draw the structural formula for alanine • Try to explain what is meant by non-superimposable mirror images (also called optical isomers). • Why is glycine the only amino acid that cannot exist in two forms which are non-superimposable mirror images of one another?

  7. H O O C C C H N H H H H H

  8. Optical isomers • Optical isomerism occurs when substances have the same molecular and structural formulae, but one cannot be superimposed on the other. • Put simply, they are mirror images of each other • No matter how hard you try, the molecule on the left will not turn into the molecule on the right – unless you break and make some bonds!

  9. H O O C H C H N H H Glycine cannot exist in two forms as the R group is only a hydrogen atom

  10. Homework • Amino acids

  11. Questions! • Which four elements are present in every amino acid? • Hydrogen, carbon, oxygen and nitrogen • Which of these elements is not present in a carbohydrate or lipid? • Nitrogen • What is the formula of the amine group? • NH2 • What is the formula of the acid group? • COOH

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