Enzymology, Catalytic Mechanism, Carbohydrate Metabolism, Adenosine Triphosphate

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Enzymology, Catalytic Mechanism, Carbohydrate Metabolism, Adenosine Triphosphate Enzymes are proteins and their function is to act as catalysts to speed up certain chemical reactions in the cell that would be slower without them. This process occurs as steps in a cycle with separate reactions in each step. If there is a missing product the step in the cycle will be incomplete and the normal function of the organism cannot be accomplished causing negative effects on the organism. The biological processed of the body would occur much more slowly or possibly not at all without the presents of enzyme reactions. Enzymes have some very specific qualities. Enzymes are sensitive to temperature and they tend to work faster as temperature increases, but they can stop working if the temperature becomes too high. Enzymes are also sensitive to pH and their ability to function will be affected if the environment is too acidic or basic for a specific enzyme. Certain chemicals can hinder an enzyme and prevent it from functioning. The inhibition of these enzymes can be temporary or permanent. Enzyme-catalyzed reactions can work both ways or are reversible. Fructose, a monosaccharide or simple sugar found in fruits, fruit juices and sweeteners such as honey and contains 6 carbons, is broken down by an enzymatic reaction. Fructose is a carbohydrate and is a good source of energy for the body, but it needs to be broken down by enzymes to become energy that can be used by the body. When fructose is consumed the first step begins with the enzyme fructokinase binding with the fructose which produces fructose-1-phosphate. The second step of the cycle takes place when the enzyme aldolase B splits the fructose-1-phosphate into 2 three carbon molecules - DHAP (dihydroxyacetone phosphate) and glyceraldehyde. At this point these two products can enter glycolysis and produce energy for the body to use. Activation energy is the minimum amount of energy needed for a chemical reaction to start. Enzymes lower activation energy. They are able to do this by temporarily combining with reactants called substrates. This mechanism is called “lock and key”. Enzymes are the lock while the substrates are the key. Enzymes have an activation site which has a specific shape that only fits to a specific substrate molecule. The substrate molecule conforms to the enzyme activation site and forms a temporary bond and is referred to as the enzyme-substrate complex. The interaction of the substrate and the enzyme stresses some of the chemical bonds in the substrate and causes them to break and form a different molecule called a product. The new product is released from the active site. The enzyme resumes its original shape and the enzyme is free to repeat the process by joining to another substrate. Aldolase B is the enzyme needed in the second step of breaking down fructose into energy that is useable. Hereditary fructose intolerance (HFI) is an autosomal condition that diminishes a person’s ability to break down fructose because the body lacks aldolase B enzyme. HFI is an inherited recessive autosomal disorder and is caused by mutations in ALDOB gene. The ALDOB gene provides the genetic code for the production of aldolase B enzyme. One of the genetic mutations that cause the defect in aldolase is found in position 149 of its peptide chain. Normally this position has the amino acid alanine, but the mutation replaces this amino acid with proline (ALDOB, 2011). This mutation changes the 3-demensional shape of the enzyme. This alteration in the shape makes it difficult for the enzyme to bind together and form tetramers (formed from 4 sub-units). If aldolase B is not a tetramer it will not be able to metabolize fructose (ALDOB, 2011).

Lock and Key Model of Enzymatic Activity

Image: Biochemistry . (n.d.). Retrieved August 22, 2012, from Biochemistry Student help: http://www.classhelp.info/Biology/AUnit3Biochemistry.htm

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