Amino acids are the compounds that are substituted by amino acids, which contain amino and carboxyl groups. Similar to hydroxy acids, amino acids can be divided into alpha-beta, gamma -... W - amino acids, but the amino acids that are obtained by proteolysis are alpha-amino acids, and there are only two dozen of them, which are the basic units that make up the protein.
Amino acids are the basic substances that make up the protein needed for animal nutrition. Organic compounds containing alkaline amino acids and acidic carboxyl groups. The amino group is alpha-amino on alpha carbon. The amino acids that make up proteins are mostly alpha-amino acids.
Amino acids can play the following roles in the body through metabolism: To become acids, hormones, antibodies, creatine, etc. Turn to carbohydrates and fats; It oxidizes carbon dioxide and water and urea, producing energy.
Amino acids as colorless, more than 200 ℃, melting point than the average much higher melting point of organic compounds. Alpha-amino acid has four different flavors of acid, sweet, bitter and fresh. Monosodium glutamate and glycine are the most used flavorings. The amino pass is generally insoluble in water, acid solution and alkali solution, not soluble or soluble in organic solvents such as ethanol or ether. Amino acids in the water solubility of the difference is very big, such as the minimum solubility tyrosine, 25 ℃, tyrosine dissolved only 0.045 g 100 g water, but in hot towel tyrosine solubility is bigger. Lysine and speramate are often present in the form of hydrochloric acid, because they are highly soluble in water and are difficult to crystallize because of the deliquescence .
(1) the color and color of various common amino acids are easy to be colorless crystals, and the crystalline shape varies with the structure of amino acids. For example, l-monoglutamic acid is a tetragon, and D monoglutamic acid is a diamond-shaped flake.
(2) amino acid crystallization of high melting point, melting point is in commonly 200 ~ 200 ℃, a lot of amino acids in at or near melting point will be broken down into amine and CO2.
(3) most amino acids of solubility are soluble in water. The solubility of different amino acids in water is different, such as lysine, arginine, and proline solubility. The solubility of tyrosine, cysteine and histidine is very small. All kinds of amino acids are soluble in strong bases and strong acids. But amino acids are insoluble or slightly soluble in ethanol.
(4) flavor amino acids and their derivatives have a certain taste, such as sour, sweet, bitter, etc. The flavor of the species is related to the type of amino acid and the three-dimensional structure. Generally speaking, the d-type amino acid has a sweet taste, and its sweet intensity is higher than the corresponding L 1 amino acid.
(5) the ultraviolet absorption properties of various common amino acids have no capacity to absorb visible light. But tyrosine, tryptophan and phenylalanine have obvious photoabsorption in ultraviolet region. Most proteins contain these three amino acids, especially tyrosine. Therefore, the content of protein can be quantitatively detected by uv absorption characteristic of 280hm wavelength.
Amino acid acid base titration curve
Glycine, for example: Moore glycine soluble in water, the solution pH is 5.97, with standard NaOH and HCl titration respectively, solution pH value as the ordinate, adding HCl and NaOH, the abscissa denotes the number of moles of drawing, the titration curve. A very important feature of this curve is that at pH=2.34 and pH= 9.60, there are two inflection points, which are pK1 and pK2 respectively. Rule: pH [R].</pk1> > pH > pK2 ', [R] [R +] > [R +]; When the pH is pI, the net charge is zero, [R]=[R-]; When the pH< pI, the net charge is "+"; When you have a pH of > pI, the net charge is "-