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Amino acids and peptide bond

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Amino acid

Amino acids are the building blocks of proteins. The main carbon (The alphaask Dr Chromo! carbon atom) is asymmetrical because the four groups linked to it are different.

There is

All 20 different amino acids have this same structure, but their side chain groups (the R group) may vary in size, shape, charge, hydrophobicityask Dr Chromo!, and reactivity. The amino acids could be considered as the alphabet in which the proteins are written. Students in biology must be familiar with the special properties of each letter of the alphabet, which are determined by the side chain (R).


Amino acid side chains are sorted into groups as follow :

In this group the side chain is aliphatic ask Dr Chromo!. An aliphatic group is hydrophobic.

Rasmol Glycine, Gly, G
Rasmol Alanine, Ala, A
Rasmol Valine, Val, V
Rasmol Leucine , Leu, L
Rasmol Isoleucine, Ile, I 		In this group the side chain is an organic acidask Dr Chromo!. The side chain is negatively charged.

Rasmol Aspartic Acid, Asp, D
Rasmol Glutamic acid, Glu, E

In this group the side chain is an amideask Dr Chromo!

  • Rasmol Asparagine, Asn, N,
  • Rasmol Glutamine, Gln, Q.
In this group the side chain contains a sulphurask Dr Chromo!. They are hydrophobic and cysteines are very reactive.
  • Rasmol Methionine, Met, M
  • Rasmol Cysteine, Cys, C
In this group the side chain is an alcoholask Dr Chromo!.
  • Rasmol Serine, Ser, S
  • Rasmol Threonine, Thr, T
  • Rasmol Tyrosine, Tyr, Y . Note, Tyrosine is also aromatic
In this group the side chain is an organic baseask Dr Chromo!. The side chain is hydrophilic.
  • Rasmol Arginine, Arg, R
  • Rasmol Lysine, Lys, K
  • Rasmol Histidine, His, H
In this group the side chain is aromaticask Dr Chromo!. The side chain is very hydrophobic.
  • Rasmol Phenylalanine , Phe, F
  • Rasmol Tryptophan, Trp, W.

In this group the side chain is an imine ask Dr Chromo!

. This amino acid is found in bends due to its structure.
  • Rasmol Proline, Pro, P.

The peptide bond

Two amino acids can, under some circumstances, react together. The result is the creation of a dipeptide. A molecule of water is released in the process. This is the basic reaction involved in the synthesis of proteins.

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