In this practical the acid-base behavior of amino acids was assessed. Amino acids are empathetic. 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 glycogen was used as a model to show this unique nature of amino acids. A series of four acid -base iterations were conducted; ml of 0. MM glycogen in solution titrated against 0.
M Noah and HCI, and ml of 0. MM glycogen in formaldehyde titrated against 0. MM Noah and HCI. The peak value of glycogen was determined. Iterations curves were constructed by reading the pH meter after every 0. Ml or Mil addition of iterant. 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 (Street,L. 999). Some proteins are globular and water soluble, like those found in blood, milk, and egg white. Others are fibrous and relatively inert. Keratin’s are proteins found in hair and wool, and collagen’s 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 carbonyl 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 praline, which has a secondary amino group and is in fact an -amino acid (Vote and Vote, 2011). Figure 1 shows the general structure of an amino acid. Adapted from http://www. Answers. Com/topic/aminoвЂўacid 20 kinds of R groups varying in size, shape, charge, hydrogen-bonding activity, and chemical reactivity are commonly found in proteins. Indeed, all proteins In all species, from bacteria to human, are constructed from the same set of amino acids Street,L. 1999). The R group determines the physiochemical structure of amino acid. 1 OFF bulky side chains. Some have aromatic R groups, others are polar. Some confer conformational inflexibility; others can participate in hydrogen bonding or covalent bonding. The amino and carbonyl groups of amino acids, along with instable R groups can participate in reactions as weak acids and bases. When amino acids with no instable R groups are in a neutral pH they exist predominantly as diploma ions, or extensions, rather than UN-unionized molecules (Homes and Hoper; 2005).
The point at which the extensions formed is called the sclerotic point (p’) of an amino acid. At the sclerotic point, the amine group shows a positive charge and the carbonyl group has a negative charge, therefore, the overall extinction form is neutral. Thus, the extinction form is the least soluble in water. Fig 2; The extinction form of an amino acid at different pH values (adapted from http://homepages. Us. Dude/DISRUPTOR/chic/amino. HTML) In acidic solution, (e. G. PH = 3. 0), the carbonyl group is unionized (-COHO) and the amino group is unionized (-NH+).
Whereas, in an alkaline solution, (e. G. PH = 9. 0), the carbonyl group is unionized (-COO-) and the amino group is unionized (-NH) (Street,L. , 1999). Fig 4;Titration curve of an amino acid (adapted from http://homepages. Us. Dude/ DISRUPTOR/chic/amino. HTML) The peak or dissociation constant is a measure of the strength of an acid or a base. It is the pH at which one-half of the acid present has reacted with the base. When the curve reaches the first of two flat regions, labeled A in Figure 4, the point where one-half of the carbonyl group is depredation is reached.
At the point of inflection, point B, the carbonyl group is completely depredation and the sclerotic point is reached. At this point the amino acid exists in extinction form. At the second of two flat regions, labeled as point C, one-half of the amine group is propionate. The sclerotic point of an amino acid can be calculated according to the following equation: Adapted from (Street,L. , 1999) This equation can be used only for amino acids that do not carry acidic or basic groups in their side chains (Stanton and Ruff, 1995).
Aim: to study the structure and H of amino acids in solution Materials: ml 0. MM glycogen, ml beaker, 0. MM HCI, 0. MM Noah, pipette, pipette filler, pH meter, burette, magnetic stirrer, glutamine acid, argentine, distilled water, formaldehyde Method The pH of distilled water, glutamine acid, argentine and glycogen were first measured. ml of 0. MM glycogen were pipette into a 50 ml beaker. The burette was then filled with 0. MM HCI an placed on a magnetic stirrer. Stirring was done after the electrode of the pH meter was adjusted to clear the stirring “flea. “pH of the solution was recorded.
The first Ml of HCI was added at 0. Ml differences, with the pH being recorded between each addition. The following Ml was added with 1 ml differences and finally the last ml was added with 0. Ml difference. This was done so as not to was repeated using 0. MM Noah for titration. PH values of the resulting solution recorded after each addition difference. Discussion Glycogen was the model amino acid in this practical. Glycogen (HEN-CHI-COHO) is a dipodic amino acid which means that it has two dissociable protons, one tote alpha amino acid and the other on the carbonyl group.
The R group in glycogen is not unusable, thus does not affect the dissociation. Acid-base titration involves gradual addition. A typical glycogen plot has two distinct stages corresponding to the deprivation of two different groups of amino acid. At very low pH, the predominant ionic species of glycogen are fully propionate +HEN-CHI-COHO. At the midpoint in the first stage of titration, in which the -COHO of glycogen loses its proton, there are equiangular concentrations of concentrations of proton donor and proton acceptor. The amino acid, glycogen is diploma at this stage I. E. Witnesses ion (+HEN-CHI-COO-). This pH in which the amino acid has zero charge is called the sclerotic point (p’). For glycogen Pl falls halfway between the two PC values. The second stage of the titration corresponds to the removal of a proton from the NH+ group of glycogen (Sadism, et al; 2005). The graph obtained the practical shows theses two distinct stages.