{"id":155,"date":"2019-06-17T18:11:58","date_gmt":"2019-06-17T22:11:58","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/3-10-chemical-reactions-in-living-things\/"},"modified":"2025-08-26T17:47:53","modified_gmt":"2025-08-26T21:47:53","slug":"3-12-chemical-reactions-in-living-things","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/3-12-chemical-reactions-in-living-things\/","title":{"raw":"3.12 Chemical Reactions in Living Things","rendered":"3.12 Chemical Reactions in Living Things"},"content":{"raw":"
\r\n\r\n[caption id=\"attachment_153\" align=\"alignright\" width=\"372\"]\"Image Figure 3.12.1. Auto assembly line.<\/em>[\/caption]\r\n\r\nCreated by:\u00a0CK-12\/Adapted by Christine Miller<\/span>\r\n

Assembly Line<\/h1>\r\n<\/div>\r\nWe stay alive because millions of different [pb_glossary id=\"1330\"]chemical reactions[\/pb_glossary] are taking place inside our bodies all the time. Each of our [pb_glossary id=\"1298\"]cells[\/pb_glossary] is like the busy auto assembly line pictured in Figure 3.12.1. Raw materials, half-finished products, and waste materials are constantly being used, produced, transported, and excreted. The \"workers\" on the cellular assembly line are mainly enzymes. These are the [pb_glossary id=\"1373\"]proteins[\/pb_glossary] that make [pb_glossary id=\"1301\"]biochemical reactions[\/pb_glossary] happen.\r\n
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What Are Biochemical Reactions?<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"1330\"]Chemical reactions[\/pb_glossary]\u00a0that take place inside living things are called\u00a0[pb_glossary id=\"1301\"]biochemical reactions[\/pb_glossary].<\/strong>\u00a0The sum of all the biochemical reactions in an organism is called\u00a0[pb_glossary id=\"1352\"]metabolism[\/pb_glossary]<\/strong>. Metabolism includes both [pb_glossary id=\"1222\"]exothermic[\/pb_glossary] (energy-releasing)\u00a0chemical reactions\u00a0and [pb_glossary id=\"1009\"]endothermic[\/pb_glossary] (energy-absorbing) chemical reactions.\r\n

Catabolic Reactions<\/h2>\r\nExothermic reactions in organisms are called\u00a0[pb_glossary id=\"1233\"]catabolic reactions[\/pb_glossary]<\/strong>. These reactions break down molecules into smaller units and release\u00a0energy. An example of a catabolic reaction is the breakdown of glucose during\u00a0cellular respiration, which releases energy that\u00a0cells\u00a0need to carry out life processes.\r\n

Anabolic Reactions<\/h2>\r\nEndothermic reactions in organisms are called\u00a0[pb_glossary id=\"1237\"]anabolic reactions[\/pb_glossary]<\/strong>. These reactions build up bigger molecules from smaller ones and absorb\u00a0[pb_glossary id=\"1342\"]energy[\/pb_glossary]. An example of an anabolic reaction is the joining of\u00a0[pb_glossary id=\"1319\"]amino acids[\/pb_glossary]\u00a0to form a\u00a0[pb_glossary id=\"1373\"]protein[\/pb_glossary]. Which type of reactions \u2014 catabolic or anabolic \u2014 do you think occur when your body digests food?\r\n
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Enzymes<\/h2>\r\n<\/div>\r\n\r\n[caption id=\"attachment_154\" align=\"alignleft\" width=\"276\"]\"Image Figure 3.12.2. The activation energy for a reaction is lowered in the presence of an enzyme<\/em>.[\/caption]\r\n\r\nMost of the biochemical reactions that happen inside of living organisms\u00a0require\u00a0help. Why is this the case? For one thing, temperatures inside living things are usually too low for biochemical reactions to occur quickly enough to maintain life. The concentrations of reactants may also be too low for them to come together and react. Where do the biochemical reactions get the help they need to proceed? From the enzymes.\r\n\r\nAn\u00a0[pb_glossary id=\"1345\"]enzyme[\/pb_glossary]<\/strong> is a [pb_glossary id=\"1373\"]protein[\/pb_glossary] that speeds up a [pb_glossary id=\"1301\"]biochemical reaction[\/pb_glossary]. It is a biological [pb_glossary id=\"1300\"]catalyst[\/pb_glossary]. An enzyme generally works by reducing the amount of [pb_glossary id=\"1225\"]activation energy[\/pb_glossary] needed to start the reaction. Figure 3.12.2 shows the activation energy needed for glucose to combine with oxygen. Less activation energy is needed when the correct enzyme is present than when it is not present.\r\n

How Well Enzymes Work<\/h2>\r\nEnzymes are involved in most biochemical reactions, and they do their jobs extremely well. A typical biochemical reaction that would take several days or even several centuries to\u00a0happen\u00a0without an enzyme is likely to occur in just a split second with the proper enzyme! Without enzymes to\u00a0speed\u00a0up biochemical reactions, most organisms could not survive.\r\n\r\nThe [pb_glossary id=\"1299\"]substrate[\/pb_glossary]<\/strong> of an enzyme is the specific substance it affects; the reactant of the reaction. Each enzyme works only with a particular substrate, which explains why there are so many different enzymes. As shown in Figure 3.12.3, the substrate must bind with a specific region on the enzyme, called the '[pb_glossary id=\"3058\"]active site[\/pb_glossary]'. The enzyme and substrate(s) form a temporary structure called the enzyme-substrate complex. While the substrate is held by the enzyme, its bonds are more easily changed so that the reaction proceeds more efficiently.\r\n\r\nBecause enzymes are complex proteins, changes in the environment can affect the internal bonding that gives the protein its shape, most importantly the shape at the active site. Therefore, enzymes need specific conditions, such as the right temperature and pH. Some enzymes work best under acidic conditions, while others work best in neutral environments.\r\n\r\n[caption id=\"attachment_3056\" align=\"aligncenter\" width=\"600\"]\"Image Figure 3.12.3 the enzyme and substrate bind, forming a temporary complex. The products are released once the reaction has occurred, and the enzyme resumes its original shape. <\/em>[\/caption]\r\n

Enzyme-Deficiency Disorders<\/h3>\r\nThere are hundreds of known inherited metabolic disorders in humans. In most of them, a single enzyme is either not produced by the body at all, or is otherwise produced in a form that doesn't work. The missing or defective enzyme is like an absentee worker on the cell's assembly line. Imagine the auto assembly line from the image at the start of this section.\u00a0 What if the worker who installed the steering wheel was absent?\u00a0 How would this impact the overall functioning of the vehicle?\u00a0 When an enzyme is missing, toxic chemicals build up, or an essential product isn't made. Generally, the normal enzyme is missing because the individual with the disorder inherited two copies of a gene mutation, which may have originated many generations previously.\r\n\r\nAny given inherited metabolic disorder is generally quite rare in the general\u00a0population. However, there are so many different metabolic disorders that a total of one in 1,000 to 2,500 newborns can be expected to have one.\r\n
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3.10 Summary<\/h1>\r\n<\/header>\r\n
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