Micrographs bottom row show wheat starch granules stained with iodine left , glycogen granules G inside the cell of a cyanobacterium middle , and bacterial cellulose fibers right.
Chitin is a structural polymer found in cell walls of fungi and exoskeletons of some animals. Skip to main content. Microbial Biochemistry. Search for:. Carbohydrates Learning Objectives Give examples of monosaccharides and polysaccharides Describe the function of monosaccharides and polysaccharides within a cell. Think about It Why do monosaccharides form ring structures?
Figure 3. Common disaccharides include maltose, lactose, and sucrose. Think about It What are the most biologically important polysaccharides and why are they important? Key Concepts and Summary Carbohydrates , the most abundant biomolecules on earth, are widely used by organisms for structural and energy-storage purposes. Carbohydrates include individual sugar molecules monosaccharides as well as two or more molecules chemically linked by glycosidic bonds.
Monosaccharides are classified based on the number of carbons the molecule as trioses 3 C , tetroses 4 C , pentoses 5 C , and hexoses 6 C. They are the building blocks for the synthesis of polymers or complex carbohydrates. Disaccharides such as sucrose, lactose, and maltose are molecules composed of two monosaccharides linked together by a glycosidic bond. Polysaccharides , or glycans , are polymers composed of hundreds of monosaccharide monomers linked together by glycosidic bonds.
The energy-storage polymers starch and glycogen are examples of polysaccharides and are all composed of branched chains of glucose molecules. The polysaccharide cellulose is a common structural component of the cell walls of organisms.
Other structural polysaccharides, such as N-acetyl glucosamine NAG and N-acetyl muramic acid NAM , incorporate modified glucose molecules and are used in the construction of peptidoglycan or chitin. Multiple Choice By definition, carbohydrates contain which elements? Carbohydrates contain carbon, hydrogen, and oxygen. Show Answer Answer d. Monosaccharides may link together to form polysaccharides by forming glycosidic bonds. Matching Match each polysaccharide with its description. C Glycogen is an energy storage polymer found in animal cells and bacteria.
Glycogen b and cellulose c are also made of thousands of glucose molecules, but organized in a branched and straight pattern, respectively.
Starch : plants, e. Our blood carries glucose to most cells in our body, where it is used as a source of energy. Our body stores extra glucose as glycogen in muscles and liver. Study Questions Write your answer in a sentence form do not answer using loose words. Concepts, terms, and facts check Study Questions Write your answer in a sentence form do not answer using loose words What is a carbohydrate? What elements are carbohydrates made of? What suffix is used to name carbohydrates?
What is the difference in structure among monosaccharides, disaccharides, and polysaccharides? List all the examples of monosaccharides, disaccharides, and polysaccharides described in the module 6. How does the body use monosaccharides, disaccharides, and polysaccharides what is their function? Monosaccharide simple sugars. Long-chain molecules, such as starches and dietary fibres, are known as complex carbohydrates.
In reality, though, there are more distinct differences. Table 1 gives an overview of the major types of carbohydrates in our diet.
Carbohydrates are also known under the following names, which usually refer to specific groups of carbohydrates 1 :. The different names come from the fact that carbohydrates are classified depending on their chemical structure, but also based on their role, or source in our diet. Even leading public health authorities have no aligned common definitions for different groups of carbohydrates 2. Simple carbohydrates — those with one or two sugar units — are also simply known as sugars.
Examples are:. Polyols, or so-called sugar alcohols, are also sweet and can be used in foods in a similar way to sugars, but have a lower calorie content compared to normal table sugar see below.
They do occur naturally, but most polyols that we use are made by the transformation of sugars. Sorbitol is the most commonly used polyol in foods and drinks, while xylitol is frequently used in chewing gums and mints. Isomalt is a polyol produced from sucrose, often used in confectionery. Polyols can have a laxative effect when eaten in too large quantities. The World Health Organization WHO defines oligosaccharides as carbohydrates with sugar units, although other definitions allow for slightly longer chain lengths.
The most well-known are oligofructans or in proper scientific terms: fructo-oligosaccharides , which consist of up to 9 fructose units and naturally occur in low sweetness vegetables such as artichokes and onions. Raffinose and stachyose are two other examples of oligosaccharides found in some pulses, grains, vegetables, and honey. Most of the oligosaccharides are not broken down into monosaccharides by human digestive enzymes and are utilised by the gut microbiota instead see our material on dietary fibres for more information.
Ten or more — and sometimes even up to several thousand — sugar units are needed to form polysaccharides, which are usually distinguished in two types:. Carbohydrates are an essential part of our diet. During digestion, carbohydrates that consist of more than one sugar get broken down into their monosaccharides by digestive enzymes, and then get directly absorbed causing a glycaemic response see below.
The body uses glucose directly as energy source in muscle, brain and other cells. Some of the carbohydrates cannot be broken down and they get either fermented by our gut bacteria or they transit through the gut without being changed. Interestingly, carbohydrates also play an important role in the structure and function of our cells, tissues and organs.
Carbohydrates broken down to mainly glucose are the preferred source of energy for our body, as cells in our brain, muscle and all other tissues directly use monosaccharides for their energy needs.
Depending on the type, a gram of carbohydrates provides different amounts of energy:. Monosaccharides are directly absorbed by the small intestine into the bloodstream, where they are transported to the cells in need.
Several hormones, including insulin and glucagon, are also part of the digestive system. They maintain our blood sugar levels by removing or adding glucose to the blood stream as needed.
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