Because of the way the subunits are joined, the glucose chains have a helical structure. Glycogen not shown is similar in structure to amylopectin but more highly branched. Glycogen is the storage form of glucose in humans and other vertebrates and is made up of monomers of glucose. Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells. Whenever blood glucose levels decrease, glycogen is broken down to release glucose in a process known as glycogenolysis.
Cellulose is the most abundant natural biopolymer. The cell wall of plants is mostly made of cellulose; this provides structural support to the cell. Wood and paper are mostly cellulosic in nature. Figure 7. Because of the way the glucose subunits are joined, every glucose monomer is flipped relative to the next one resulting in a linear, fibrous structure. As shown in Figure 7, every other glucose monomer in cellulose is flipped over, and the monomers are packed tightly as extended long chains.
This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. In these animals, certain species of bacteria and protists reside in the rumen part of the digestive system of herbivores and secrete the enzyme cellulase.
The appendix of grazing animals also contains bacteria that digest cellulose, giving it an important role in the digestive systems of ruminants.
Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal. Termites are also able to break down cellulose because of the presence of other organisms in their bodies that secrete cellulases.
Figure 8. Insects have a hard outer exoskeleton made of chitin, a type of polysaccharide. Carbohydrates serve various functions in different animals. Arthropods insects, crustaceans, and others have an outer skeleton, called the exoskeleton, which protects their internal body parts as seen in the bee in Figure 8.
This exoskeleton is made of the biological macromolecule chitin, which is a polysaccharide-containing nitrogen. Chitin is also a major component of fungal cell walls; fungi are neither animals nor plants and form a kingdom of their own in the domain Eukarya. Carbohydrates are a group of macromolecules that are a vital energy source for the cell and provide structural support to plant cells, fungi, and all of the arthropods that include lobsters, crabs, shrimp, insects, and spiders.
Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides depending on the number of monomers in the molecule. Monosaccharides are linked by glycosidic bonds that are formed as a result of dehydration reactions, forming disaccharides and polysaccharides with the elimination of a water molecule for each bond formed. Glucose, galactose, and fructose are common monosaccharides, whereas common disaccharides include lactose, maltose, and sucrose.
Starch and glycogen, examples of polysaccharides, are the storage forms of glucose in plants and animals, respectively.
The long polysaccharide chains may be branched or unbranched. Cellulose is an example of an unbranched polysaccharide, whereas amylopectin, a constituent of starch, is a highly branched molecule. Storage of glucose, in the form of polymers like starch or glycogen, makes it slightly less accessible for metabolism; however, this prevents it from leaking out of the cell or creating a high osmotic pressure that could cause excessive water uptake by the cell.
Improve this page Learn More. Skip to main content. What monosaccharides are in sucrose? What monosaccharides are in maltose?
What carbohydrates are in milk? Structurally, how does a polysaccharide differ from a polypeptide? How many disaccharides of d-glucopyranose are possible?
How do polysaccharides differ structurally and functionally from simple carbohydrates? See all questions in Carbohydrates. Importantly, carbohydrates provide energy to the body, particularly through glucose, a simple sugar that is a component of starch and an ingredient in many basic foods. Carbohydrates : Carbohydrates are biological macromolecules that are further divided into three subtypes: monosaccharides, disaccharides, and polysaccharides.
Like all macromolecules, carbohydrates are necessary for life and are built from smaller organic molecules. Carbohydrates have been a controversial topic within the diet world.
People trying to lose weight often avoid carbs, and some diets completely forbid carbohydrate consumption, claiming that a low-carb diet helps people to lose weight faster.
Carbohydrates should be supplemented with proteins, vitamins, and fats to be parts of a well-balanced diet. Calorie-wise, a gram of carbohydrate provides 4. Carbohydrates contain soluble and insoluble elements; the insoluble part is known as fiber, which is mostly cellulose.
Fiber has many uses; it promotes regular bowel movement by adding bulk, and it regulates the rate of consumption of blood glucose. Fiber also helps to remove excess cholesterol from the body. Fiber binds and attaches to the cholesterol in the small intestine and prevents the cholesterol particles from entering the bloodstream.
Then cholesterol exits the body via the feces. Fiber-rich diets also have a protective role in reducing the occurrence of colon cancer. In addition, a meal containing whole grains and vegetables gives a feeling of fullness.
As an immediate source of energy, glucose is broken down during the process of cellular respiration, which produces adenosine triphosphate ATP , the energy currency of the cell. Eliminating carbohydrates from the diet is not the best way to lose weight. A low-calorie diet that is rich in whole grains, fruits, vegetables, and lean meat, together with plenty of exercise and plenty of water, is the more sensible way to lose weight.
Privacy Policy. Skip to main content. Biological Macromolecules. Search for:. Carbohydrate Molecules Carbohydrates are essential macromolecules that are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.
Learning Objectives Describe the structure of mono-, di-, and poly-saccharides. Key Takeaways Key Points Monosaccharides are simple sugars made up of three to seven carbons, and they can exist as a linear chain or as ring-shaped molecules. Glucose, galactose, and fructose are monosaccharide isomers, which means they all have the same chemical formula but differ structurally and chemically. Disaccharides form when two monosaccharides undergo a dehydration reaction a condensation reaction ; they are held together by a covalent bond.
Sucrose table sugar is the most common disaccharide, which is composed of the monomers glucose and fructose. A polysaccharide is a long chain of monosaccharides linked by glycosidic bonds; the chain may be branched or unbranched and can contain many types of monosaccharides.
Key Terms isomer : Any of two or more compounds with the same molecular formula but with different structure. Importance of Carbohydrates Carbohydrates are a major class of biological macromolecules that are an essential part of our diet and provide energy to the body.
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