Therefore every disaccharide is composed of two chemical rings. The bond between two monosaccharides is called a glycosidic bond. Disaccharides are also simple sugars. Disaccharides are classified into two groups according to their reducing strength. Figure Structure of a Disaccharide. Therefore, some disaccharides are reducing sugars and some are not. All disaccharides are water soluble and colorless when dissolved in water. Some disaccharides are sweet tasting but some are not.
A polysaccharide is a carbohydrate made out of a number of monosaccharides linked via glycosidic bonds. Polysaccharides are chains of monosaccharides. Therefore, every polysaccharide is composed of a number of chemical rings. The formation of a polysaccharide occurs via condensation polymerization since a water molecule is formed per every glycosidic bond.
Figure Structure of a Polysaccharide. Most polysaccharides are insoluble in water and do not have a sweet taste. Almost all polysaccharides are non-reducing agents due to their complex structure. Monosaccharides: Monosaccharides are single sugar molecules which act as the building blocks of disaccharides and polysaccharides. Disaccharides: Disaccharides are sugar molecules composed of two monosaccharides.
Polysaccharides: Polysaccharides are carbohydrates made out of a number of monosaccharides linked via glycosidic bonds. Monosaccharides: Monosaccharides are water soluble. An alpha bond is formed when the OH group on the carbon-1 of the first glucose is below the ring plane, and a beta bond is formed when the OH group on the carbon-1 is above the ring plane. Figure 4. Sucrose is formed when a monomer of glucose and a monomer of fructose are joined in a dehydration reaction to form a glycosidic bond.
In the process, a water molecule is lost. By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group. In sucrose, a glycosidic linkage is formed between carbon 1 in glucose and carbon 2 in fructose. Common disaccharides include lactose, maltose, and sucrose Figure 5.
Lactose is a disaccharide consisting of the monomers glucose and galactose. It is found naturally in milk. Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose molecules.
The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose. Figure 5. Common disaccharides include maltose grain sugar , lactose milk sugar , and sucrose table sugar. The chain may be branched or unbranched, and it may contain different types of monosaccharides.
The molecular weight may be , daltons or more depending on the number of monomers joined. Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of a mixture of amylose and amylopectin both polymers of glucose.
The starch in the seeds provides food for the embryo as it germinates and can also act as a source of food for humans and animals. The starch that is consumed by humans is broken down by enzymes, such as salivary amylases, into smaller molecules, such as maltose and glucose. The cells can then absorb the glucose.
The numbers and refer to the carbon number of the two residues that have joined to form the bond. Figure 6. Amylose and amylopectin are two different forms of starch. Because of the way the subunits are joined, the glucose chains have a helical structure. Unlike mono- and disaccharides, polysaccharides are not sweet and, in general, they are not soluble in water.
Like disaccharides, the monomeric units of polysaccharides are linked together by glycosidic bonds. Polysaccharides are very diverse in their structure. Three of the most biologically important polysaccharides— starch , glycogen , and cellulose —are all composed of repetitive glucose units, although they differ in their structure Figure 4. Cellulose consists of a linear chain of glucose molecules and is a common structural component of cell walls in plants and other organisms.
Glycogen and starch are branched polymers; glycogen is the primary energy-storage molecule in animals and bacteria, whereas plants primarily store energy in starch. The orientation of the glycosidic linkages in these three polymers is different as well and, as a consequence, linear and branched macromolecules have different properties.
Modified glucose molecules can be fundamental components of other structural polysaccharides. Examples of these types of structural polysaccharides are N-acetyl glucosamine NAG and N-acetyl muramic acid NAM found in bacterial cell wall peptidoglycan. Polymers of NAG form chitin , which is found in fungal cell walls and in the exoskeleton of insects. Figure 4. Starch, glycogen, and cellulose are three of the most important polysaccharides.
In the top row, hexagons represent individual glucose molecules. 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. The difference in the colour intensity depends on the quantity of the amount of reducing sugar is present in the sample being tested. A reducing sugar is a sugar within its structure and has a free aldehyde or ketone body that has the capability of acting as a reducing agent.
Polysaccharides also known as polymers, are long complex chains of many monosaccharides that are joined together by glyosidic bonds. They are formed by a series of condensation reaction and yield more than 10 molecules monosaccharides on hydrolysis. Their properties are summarized in Table 2.
Their general formula is C 6 H 10 O 5 n. Unlike both monosaccharides and disaccharides, polysaccharides are insoluble and not sugars. They are very large molecules macromolecules and the feature of them being insoluble makes them suited for storage. Difference between monosaccharide, disaccharide and polysaccharide. Join now If you're ready to pass your A-Level Biology exams, become a member now to get complete access to our entire library of revision materials.
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