This document discusses amino acids, which are the building blocks of proteins. It notes that there are 20 common amino acids that make up proteins. All amino acids have an amino group, a carboxyl group, and a side chain except for glycine. The side chains give each amino acid unique properties. Amino acids can be classified based on the properties of their side chains, such as polarity. Some amino acids are essential for animals to obtain through their diets as animals cannot synthesize them. The essential amino acids vary slightly between different animal species. The document provides details on various amino acid properties and classifications.
2. Introduction
• Proteins are the most abundant biological macromolecules
• Occurring in all cells and all parts of cells
• Proteins also occur in great variety
• Proteins exhibit enormous diversity of biological function
• Proteins are constructed from the same ubiquitous set of 20 amino acids
• In common with carbohydrates and fats they contain carbon, hydrogen and oxygen
• But in addition they all contain nitrogen and generally sulphur
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3. Amino Acids
• Amino acids are produced when proteins are hydrolysed by enzymes, acids or alkalis
• Over 200 amino acids have been isolated from biological materials
• Only 20 of these are commonly found as components of proteins
• All 20 of the common amino acids are α-amino acids
• They have a carboxyl group (–COOH) and an amino group (–NH2)
• Both are bonded to the same carbon atom; α-carbon
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4. Amino acids
• This structure is common to all amino acids
• Proline, a cyclic amino acid, is the exception
• The R group or side chain (red) s different in each amino acid
• They differ from each other in their side chains, or R groups
• R group vary in:
• Structure
• Size
• Electric charge
• The solubility of the amino acid in water
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5. Amino acids
• For all the common amino acids except glycine
• The a-carbon is bonded to four different groups:
• A carboxyl group
• An amino group
• An R group
• And a hydrogen atom
• In glycine, the R group is another hydrogen atom
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6. Amino acids
• Carbons are numbered beginning with the terminal aldehyde or carboxyl carbon (red)
• They are numbered from top to bottom
• The R group of the amino acid is always below the a-carbon
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7. Properties of Amino Acids
• Amino acids are amphoteric i.e. they have both basic and acidic properties
• Zwitterions
• Isoelectric point
• All the α-amino acids except glycine are optically active
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8. Classification by of Amino Acids
• Amino acids can be grouped into five main classes
• This is based on the properties of their R groups:
• Particularly their polarity
• Polarity of R group varies widely
• From nonpolar and hydrophobic (water-insoluble)
• To highly polar and hydrophilic (water-soluble)
• Or tendency to interact with water at biological pH (near pH 7.0)
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9. Groups of Amino acids
• Nonpolar, Aliphatic R Groups
• Aromatic R Groups
• Polar, Uncharged R Groups
• Positively Charged (Basic) R Groups
• Negatively Charged (Acidic) R Groups
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10. Nonpolar, Aliphatic R Groups
• R groups are nonpolar and hydrophobic
• Tend to cluster together within proteins
• Hence stabilizing protein structure by means of hydrophobic interactions
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11. Aromatic R Groups
• Have aromatic side chains
• Are relatively nonpolar (hydrophobic)
• All can participate in hydrophobic interactions
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12. Polar, Uncharged R Groups
• R group are more soluble in water
• Or more hydrophilic than nonpolar amino acids
• Contain functional groups that form hydrogen bonds with water
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13. Positively Charged (Basic) R Groups
• The most hydrophilic R groups are those that are either positively or negatively charged
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14. Negatively Charged (Acidic) R Groups
• The two amino acids having R groups with a net negative charge at pH 7.0
• These are aspartate and glutamate
• Each of which has a second carboxyl group
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15. Uncommon Amino acids
• Some uncommon amino acids found in proteins
• All are derived from common amino acids
• Extra functional groups added by modification reactions
• 4-hydroxyproline, a derivative of proline
• 5-hydroxylysine, derived from lysine
• у-carboxyglutamate
• Desmosine
• Selenocysteine
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16. Essential Amino acids
• Plants and microorganisms are capable of synthesise proteins from simple nitrogenous
compounds such as nitrates
• Animals cannot synthesize the amino group
• In order to build up body proteins they must have a dietary source of amino acids
• Certain amino acids can be produced from others by a process known as transamination
• But the carbon skeletons of a number of amino acids cannot be synthesised in the animal body
• These are referred to as essential or indispensible amino acids
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18. Essential Amino acids in Poultry
• The chick requires a dietary supply of all the ten amino acids
• In addition, a chick requires a dietary source of glycine
• Birds require arginine because their metabolism does not include the urea cycle
• Poultry have a limited capacity to synthesise proline
• The actual dietary requirement of certain essential amino acids is dependent upon the
presence of other amino acids
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19. Essential Amino acids in Pigs
• Pigs require all the essential amino acids listed up
• However pigs do synthesise their own Arginine
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20. Essential Amino acids in Ruminants
• Rumen microorganisms can synthesise all the essential amino acids
• Theoretically ruminants are independent of a dietary source
• This is true once the rumen microorganisms have become established
• However supply of amino acids from microbial protein is limited in quantity and quality
• This may hinder maximum growth and production rates
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21. Essential Amino acids in Ruminants
• Biological value of microbial protein is limited by its content of certain essential amino acids
• Particularly lysine and methionine
• For maximum productivity;
• Microbial protein must be supplemented with a supply of dietary amino acids
• This can be derived from foods or synthetic amino acids
• This must be in a suitable form that is not degraded by the microorganisms in the rumen
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22. Essential Amino acids in Growing Animals
• Rapidly growing animals may respond to arginine
• This is because the very active metabolism of the liver utilises most of the amino acid
• This results in little of the amino acid being available to the general circulation
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23. Essential Amino acids in Growing Animals
• Rapidly growing animals may respond to arginine
• This is because the very active metabolism of the liver utilises most of the amino acid
• This results in little of the amino acid being available to the general circulation
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