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7 Cards in this Set
- Front
- Back
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Describe the general structure of an amino acid |
It contains a carboxylic acid group , an amino group attached to the alpha carbon in an L configuration, a hydrogen atom and a chemical group called a side chain that is different for each amino acid. |
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Discuss how the side chain of an amino acid contributes to either the functionality of the amino acid and/or the structure of the protein. |
The chemical properties of the side chain determine the types of bonds and interactions each amino acid in a polypeptide chain can make with other molecules. They are grouped by polarity of the side chain or structural features. Hydrophobic AAs cluster together to exclude water in the hydrophobic effect. The uncharged polar AAs participate in H-bonding. The negatively charged AAs acidic amino acids form ionic bonds with positively charged molecules such as the basic AAs. |
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Know the approximate pKa of the amino and carboxyl groups of the amino acids, and the pKa's for the charged side chains. |
The charge on the AA ar a particular pH is determined by the pKa of each group that has a dissociable proton. 2-3 Carboxyl group 4- acidic side chain 10-12 basic side chain 11 Amino group |
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Apply the HH to the amino acids. Be able to determine the charge of a free amino acid at a given pH. |
At physiologic pH the amino group on these amino acids carries a positive charge and the carboxylic acid group is negatively charged. The pKa of he primary carboxylic acid group is about 2. At pH much lower than the pKa all of the carboxylic acid groups are protonated. At the pKa 50% of the molecules are dissociated. The pKa for the alpha amino groups is about 9-11 so that at the lower pH of 7.4 most of the amino groups are fully protonated and carry a positive charge. |
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Calculate the pI of a free amino acid, define pI of a protein. |
the pKa of the COOH + pKA of NH3 divided by 2 (the pH at which the net charge on the molecules in solution is zero is called the pI ) Zwitterion form Protein will not move in an electric field |
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Relationship between pI and pH |
1. Isoelectric pH or pI = pH at which the amino acid or protein is in its zwitterion form 2. pI is a constant value for a molecule at a particular ionic strength and temperature (pH (pH>pI) then protein charge is negative |
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Describe how physical characteristics of proteins are used for protein purification and/or identification |
size, charge, and affinity are used for purification. |
