- Any condition that affects the three-dimensional shape of an enzyme will effect its activity.
- Two such factors that affect enzyme activity are temperature and pH.
- The shape of a protein is determined by its hydrogen bonds. Hydrogen bonds are easily disrupted by temperature changes. For example, most higher mammals have enzymes that function best within a relatively narrow temperature range between 35°C and 40°C. Below 3SX. the bonds that determine protein shape are not flexible enough to permit the
shape change necessary for substrate to tit into a reactive site. - Above 40°C, the bonds are too weak to hold the protein in proper position and maintain its shape.
- When proper shape is lost, the enzyme is destroyed, this loss of shape is called denaturation.
- The enzyme action is like a ‘lock-and-key’ fit.
- Most enzymes also have a pH optimum, usually between 6 and 8. For example, when the pH is too low, the H+ ions combine with the R-groups of the enzyme's amino adds, reducing their ability to bind with substrate.
- Acid environments can also denature enzymes. That is why some enzymes function at a low pH. For example, pepsin is the enzyme found in the stomach of mammals and has an optimal pH of approximately 2.
- Conversely trypsin is active in the more basic medium (pH 9) and found in small intestine. Overall the pH optimum of an enzyme reflects the pH of the body fluid in which the enzyme is found.
December 14th, 2011 | Posted in Vertebrate Zoology | No Comments
- All enzymes are proteins.
- An enzyme molecule may contain one or more polypeptide chains.
- The sequence of amino acids within the polypeptide chains is characteristic for each enzyme, and is believed to determine the unique three-dimensional conformation in which the chains are folded.
- This conformation, which is necessary for the activity of the enzyme, is stabilized by interactions of amino acids in different parts of the peptide chains with each other and with the surrounding medium. These interactions are relatively weak and may be
disrupted readily by high temperatures, acid or alkaline conditions or changes in the polarity of the medium. - Such changes lead to an unfolding of the peptide chains (denaturation) and a uncomitant loss of enzymatic activity, solubility and other properties, characteristic of the active enzyme.
- Because enzyme molecules are generally globular proteins, their shape and functions may be affected by pH changes in the aqueous environments.
- Denaturation by extremes of pH Is usually reversible, not so denaturation by heat.
Temperature increase will raise the rate of collision of enzyme and substrate molecules, thus increasing the rate of enzyme-substrate (ES) complex formation and raising the reaction rate. - This is opposed by increased enzyme denaturation as the optimum temperature for the reaction is exceeded.
December 13th, 2011 | Posted in Vertebrate Zoology | No Comments
- Enzymes are globular protein molecules that have three-dimensional shape with atleast one surface region having an area with a crevice or pocket.
- The crevice occupies only a small portion of the enzyme's surface and is known as its active site.
- Their shape often provide them with one or more active sites (domains) which bind temporarily and usually non-covalently with compatible substrate molecules to form one or more enzyme-substrate (ES) complexes, catalysis occurring only during the brief existence of the complex.
- Active site is so shaped so that a substrate molecule or several molecules fit into it in a very specific way and is held in place by weak chemical forces, such as hydrogen bonds.
- Binding of the substrate to the enzyme causes a change in an enzyme's shape. This phenomenon of change in an enzyme's shape following binding of substrate is called 'induced fit'. This induced fit theory is supported by X-ray crystallography evidence.
- Enzymes do nothing but speed up the rates at which the equilibrium positions of reversible reactions are attained.
December 12th, 2011 | Posted in Vertebrate Zoology | No Comments
- Kirchhoff (1815)-First indicated the occurrence of enzymes in living systems.
- Louis Pasteur (1860)-Discovered that the fermentation of food stuffs can be brought about by yeast cells.
- Kuhne (1878)-First gave the term ‘enzyme'.
- Buchner (1897)-First prepared a pure extract of "Zymase' enzyme from yeast.
- Nobel Laureate Sumner (1926)-First prepared pure crystals of 'urease' enzymes from jack beans.
- Northrop (1930)-Prepared pure crystals of the enzymes pepsin and trypsin respectively from gastric juice and pancreatic juice.
- Lock and Key or Template hypothesis was given by Emil Fischer (1894) and modified by Koshland (1971).
December 12th, 2011 | Posted in Vertebrate Zoology | No Comments
- Enzymes are proteins having enormous catalytic power, they greatly enhance the rate at which specific chemical reactions take place.
- Enzymatic reactions are always reversible.
- Almost all enzymes are globular proteins consisting either of a single polypeptide or two or more polypeptides held together by non-covalent bonds.
- Enzymes act upon other molecules (substrate) and thus catalyze chemical reaction.
- Thus, an enzyme is a biological catalyst that is capable of accelerating a specific chemical reaction by lowering the required activation energy, but unaltered itself in the process.
- The reactants of enzymatic reactions are called 'substrate'.
December 12th, 2011 | Posted in Vertebrate Zoology | No Comments
