Plants synthesize glucose using carbon dioxide and water, and glucose in turn provides energy requirements for the plant. During cellular respiration, energy releases from glucose, and that energy helps make adenosine triphosphate (ATP). In humans, glucose is an important source of energy. The chemical formula for glucose is C 6H 12O 6. Trioses, pentoses, and hexoses have three-, five-, and six- carbon backbones, respectively. Aldoses have a carbonyl group (indicated in green) at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain. Figure 3.4 illustrates monosaccharides.įigure 3.4 Scientists classify monosaccharides based on the position of their carbonyl group and the number of carbons in the backbone. Depending on the number of carbons in the sugar, they can be trioses (three carbons), pentoses (five carbons), and/or hexoses (six carbons). If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R'), it is a ketose. Most monosaccharide names end with the suffix -ose. In monosaccharides, the number of carbons usually ranges from three to seven. Monosaccharides (mono- = “one” sacchar- = “sweet”) are simple sugars, the most common of which is glucose. Scientists classify carbohydrates into three subtypes: monosaccharides, disaccharides, and polysaccharides. This formula also explains the origin of the term “carbohydrate”: the components are carbon (“carbo”) and the components of water (hence, “hydrate”). In other words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. The stoichiometric formula (CH 2O) n, where n is the number of carbons in the molecule represents carbohydrates. Carbohydrates also have other important functions in humans, animals, and plants. Grains, fruits, and vegetables are all natural carbohydrate sources that provide energy to the body, particularly through glucose, a simple sugar that is a component of starch and an ingredient in many staple foods. Carbohydrates are, in fact, an essential part of our diet. Athletes, in contrast, often “carb-load” before important competitions to ensure that they have enough energy to compete at a high level. To lose weight, some individuals adhere to “low-carb” diets. Most people are familiar with carbohydrates, one type of macromolecule, especially when it comes to what we eat. List common monosaccharides, disaccharides, and polysaccharides. Discuss the role of carbohydrates in cells and in the extracellular materials of animals and plants.By the end of this section, you will be able to do the following:
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