What makes monosaccharides different

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.

Learning Objectives Describe the benefits provided to organisms by carbohydrates. Key Takeaways Key Points Carbohydrates provide energy to the body, particularly through glucose, a simple sugar that is found in many basic foods. Carbohydrates contain soluble and insoluble elements; the insoluble part is known as fiber, which promotes regular bowel movement, regulates the rate of consumption of blood glucose, and also helps to remove excess cholesterol from the body.

It is also a component of pectin and can be a major component of gums gum Arabic. Bacterial action in making silage can yield free arabinose. Arabans are polymers of arabinose. D-xylose — there are small amounts of D-xylose free in fruits, but it occurs mainly in hemicellulose, as xylans and hetero-xylans.

Hemicellulose is a polysaccharide of xylose and arabinose a heteroxylan. The ratio of xylose to arabinose seems to affect digestibility as digestibility is reduced as the proportion of xylose increases.

Hemicelluloses constitute a considerable portion of the cell walls of plants so herbivores eat large amounts of them. These sugars are all aldopentoses. D-glucose — an aldohexose with various common names, including grape sugar, dextrose, corn sugar made from cornstarch.

Occurs free in plants, fruits, honey, body fluids, including CSF, blood, lymph. It is the major end-product of CHO digestion by non-ruminants and is therefore a primary energy form for non-ruminants.

It is a major component of many oligosaccharides with galactose forms lactose and polysaccharides such as starch and cellulose. In solution D-glucose exists as an equilibrium mixture of the straight chain form with two pyranose ring forms. Effectively, carbon atom number one reacts with carbon atom number five forming a ring. In fact two forms of the structure exist, called anomers. If the hydrogen atom is above carbon atom one then it is called an alpha anomer but if the hydrogen atom is below the carbon atom it is called a beta anomer.

This structural information is very important because it governs how molecules of glucose join together to form larger molecules.

Starch is a polymer of the a- form and is water soluble and digestible by animal enzymes. Monosaccharides are often colorless, crystalline solids, and sweet-tasting. They can be dissolved in water and occur as syrups or liquid sugar. Just like the other carbohydrates, monosaccharides are organic compounds. Monosaccharides can be classified by the number of carbon atoms they contain.

The groups are as follows:. Fructose , glucose , and galactose are regarded as dietary monosaccharides since they are readily absorbed by the small intestines.

They are hexoses with a chemical formula: C 6 H 12 O 6. Glucose and galactose are aldoses whereas fructose is a ketose. Glucose is a monosaccharide that occurs naturally and is ubiquitous. It can join with other monosaccharide units to form disaccharide s: maltose i. Glucose is one of the products of photosynthesis in plants and other photosynthetic organisms.

In plants, glucose molecules are stored as repeating units of sugar e. It is also an important component of amylopectin and cellulose. Thus, it occurs abundantly in fruits, plant juices, and many other plant organs.

It also serves as an important metabolic intermediate of cellular respiration and a major source of energy via aerobic respiration or anaerobic respiration. In animals, it circulates in the blood and as such referred to as blood sugar. An excess of glucose in animals is stored as glycogen. Galactose is similar to glucose in terms of chemical structure. However, the orientations of H and OH on carbon 4 are exchanged. Unlike glucose, galactose generally does not occur in free state. It usually is a constituent of complex biomolecules.

For instance, galactose together with glucose forms lactose milk sugar , which is a disaccharide. Lactose , the disaccharide of milk, consists of galactose joined to glucose by a - glycosidic link.

Galactose catabolism where glucose is converted to glucose is carried out via the Leloir pathway. In human lactation, one of the sources of lactose in breast milk is through de novo synthesis of galactose and glucose through hexoneogenesis.

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. 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.