Metabolism: Cellular Respiration and New World Encyclopedia

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Running head: METABOLISM

February 12, 2013
Western Governor’s University

Enzymes are molecules that are responsible for chemical reactions that occur within the body. They act as catalyst by accelerating metabolic reactions from the digestion of foods to synthesizing deoxyribonucleic acid (DNA). An enzymatic reaction changes substrates, the beginning molecule, into products. Enzymes are selective for the type of substrate that they will bind to; they have specific shapes that fit into one another like a lock and key as illustrated in figure 1 and 2 below. Enzymes (Figure 1,

(Figure 2,
work together in specific orders and create metabolic pathways; this is how enzymes take on the product of other enzymes as substrates. In doing so, catalytic reactions occur and the products formed are then passed onto another enzyme. Enzymes work by lowering the activation energy for reactions; this speeds up the rate of the reaction process as illustrated in figure 3 below (Grisham, 2012). (Figure 3,

An example of how enzymes work within the body is the breakdown of fructose. Energy obtained from carbohydrates goes through a process called glycolysis. Glycolysis a series of biochemical reactions in which one glucose molecule is oxidized into two pyruvic acid molecules and a small amount of adenosine triphosphate (ATP). Generation of high energy molecules are used as cellular energy sources in aerobic and anaerobic respiration. The products formed through glycolysis usually enter into the citric acid cycle and the electron transport chain to produce more energy. Fructose enters the glycolytic pathway through the liver or skeletal muscle. For example, in the liver, fructose is phosphorylated by the enzyme fructokinase to fructose-1 phosphate. The six carbon fructose is split into three carbon molecules, glyceraldehyde and dihydroxyacetone phosphate. Glyceraldehyde is then phosphorylated by another enzyme so it can also enter into the glycolytic pathway (New world encyclopedia, 2008).

Hereditary fructose intolerance (HFI) is a disease that is caused from a mutation in the liver isozyme fructaldolase, also known as adolase B. Adolase B is found in the liver and is directly involved in the metabolism of fructose. “Fructose from the diet is phosphorylated by fructonkinase to form fructose-1-phosphate, the specific substrate of adolase B. In individuals with HFI, who lack adolase B, fructose challenge leads to the accumulation of fructose-1-phosphate and thereby to the sequestrian of inorganic phosphate. In this environment, the activation of the liver phosphorylase (which is required for glucose formation) is prevented, and purine nucleotide breakdown is initiated. Glucose formation is subsequently halted by inhibiting both gluconeogenesis and glycogenolysis, and fructokinase activity is eventually inhibited. Hypoglycemia, fructosemia, hyperuricemia, and acidosis result from the arrested metabolism” (Cox, 2002, pg. 7-8). The ALDOB gene is responsible for making the adolase B enzyme. Mutations in the ALDOB gene cause HFI. This mutation changes the shape of adolase B, therefore it is difficult for the enzyme to form a tetramer, and if it cannot form a tetramer it cannot metabolize fructose (Genetics home reference, 2011).

Mitochondria create energy needed for the body to function properly. Mitochondrial disease results when there is a dysfunction in the way the mitochondria convert the energy of food molecules into ATP. When this dysfunction occurs, less energy is created for the body to use. This can lead to cell injury and cell death. Mitochondrial disease can cause loss of motor control, muscle weakness and pain, gastrointestinal disorders, swallowing difficulties, cardiac disease, liver dysfunction, lactic acidosis, and numerous other problems. (What is mitochondrial, n.d.).

(Figure 4)
The Cori cycle is...
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