This unusual type of molecule is essential to all living things. It has a basic group (i.e. NH2) at one end and an acidic group (i.e. COOH) at the other end. This means that the molecules can have dual basic and acidic properties, depending on what environment it is in. This is an important property for molecules so vital for our body cells, which are subject to many changes of acidity.
The acidity of a solution is more quantitatively defined as a pH value. This is a term that expresses the hydrogen ion concentration on a 1–14 scale. Solutions with pH 1–6 show acidic properties, pH 7 is neutral and solutions with pH 8–14 are basic.
The lower the acidic scale is, the more acidic the solution; alternatively, above 7, the more basic a solution is, the greater the value. As the pH of a solution is altered, the following changes occur in amino acids.
Starting as a neutral non-charged amino acid molecule, suppose more acid (Hþ) is added. It changes from an electrically neutral molecule to a positively charged ion, NH3þCH2 COOH. If now it is subjected to an alkaline environment due to OH ions being present, then a doubly charged ion (both positive and negative charges are present on the molecule), NH3þCH2 COO , is formed, and eventually a negatively charged ion, NH2CH2COO (as H is removed from the NHsþgroup). The reverse set of formulae would occur if an acid (Hþ) was added to the NH2 CH2 COO ion These cycles of changes help to maintain the best working pH for the body cells, which are made up of proteins and amino acids.
The charged amino acid molecules make excellent controllers of the acidity of an environment, in cells, and in body fluids, including in the stomach, as they can ‘soak up’ excess acid or alkali. The protein structures on the lining of the stomach help to stabilize the acidity in it and to control the pH. These pH values can often be
disturbed by over-eating or -drinking.
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