The Behavior of Amino Acids in Solutions
PRACTICAL III: THE BEHAVIOUR OF AMINO ACIDS IN SOLUTION
Abstract
In this practical the acid-base behaviour of amino acids was assessed. Amino acids are amphoteric. They have the basic (amine) and the acidic (carboxylic) functional groups. These show the same type of equilibrium reactions that all weak acids and bases undergo, and the relative amount of each can be altered by adjusting the pH of the solution. For this practical glycine was used as a model to show this unique nature of amino acids. A series of four acid –base titrations were conducted; 25ml of 0.1M glycine in solution titrated against 0.2M NaOH and HCl, and 25ml of 0.1M glycine in formaldehyde titrated against 0.2M NaOH and HCl. The pKa value of glycine was determined. Titrations curves were constructed by reading the pH meter fter every 0.5ml or 1ml addition of titrant.
Introduction
Proteins are large molecules found in the cells of living organisms and in biological fluids. They play crucial roles in virtually all biological processes. The major functions of proteins can be summarized as: enzymatic catalysis, control of growth and differentiation, transport and storage, coordinated motion, mechanical support (Stryer,L., 1999). Some proteins are globular and water soluble, like those found in blood, milk, and egg white. Others are fibrous and relatively inert. Keratins are proteins found in hair and wool, and collagens are the proteins found in connective tissues such as tendons. Proteins have molecular weights ranging from five thousand to several million atomic units (Stanton and Ruff, 1995).
Proteins are condensation polymers composed of 20 different alpha amino acids. Alpha amino acids are composed of a carboxyl group, an amino group, a hydrogen atom and a distinctive R group attached to an alpha carbon. This carbon is so named because it is adjacent to a carboxylic group. Of the 20 standard amino acids, the one exception to this general structure is proline, which has a
Abstract
In this practical the acid-base behaviour of amino acids was assessed. Amino acids are amphoteric. They have the basic (amine) and the acidic (carboxylic) functional groups. These show the same type of equilibrium reactions that all weak acids and bases undergo, and the relative amount of each can be altered by adjusting the pH of the solution. For this practical glycine was used as a model to show this unique nature of amino acids. A series of four acid –base titrations were conducted; 25ml of 0.1M glycine in solution titrated against 0.2M NaOH and HCl, and 25ml of 0.1M glycine in formaldehyde titrated against 0.2M NaOH and HCl. The pKa value of glycine was determined. Titrations curves were constructed by reading the pH meter fter every 0.5ml or 1ml addition of titrant.
Introduction
Proteins are large molecules found in the cells of living organisms and in biological fluids. They play crucial roles in virtually all biological processes. The major functions of proteins can be summarized as: enzymatic catalysis, control of growth and differentiation, transport and storage, coordinated motion, mechanical support (Stryer,L., 1999). Some proteins are globular and water soluble, like those found in blood, milk, and egg white. Others are fibrous and relatively inert. Keratins are proteins found in hair and wool, and collagens are the proteins found in connective tissues such as tendons. Proteins have molecular weights ranging from five thousand to several million atomic units (Stanton and Ruff, 1995).
Proteins are condensation polymers composed of 20 different alpha amino acids. Alpha amino acids are composed of a carboxyl group, an amino group, a hydrogen atom and a distinctive R group attached to an alpha carbon. This carbon is so named because it is adjacent to a carboxylic group. Of the 20 standard amino acids, the one exception to this general structure is proline, which has a
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