All Rights Reserved. Date last modified: March 22, Created by Wayne W. Basic Cell Biology. Table of Contents All Modules. More Complex Biological Molecules Carbohydrates Sugar Molecules The stuff of life is amazingly diverse and complex, but it is all based on combinations of simple biological molecules.
For example, the hydroxyl group -OH consists of a hydrogen atom bonded to an oxygen atom: The hydoxyl group will commonly be bonded to a carbon atom in this fashion: And this structure might be found, for example, as part of a glucose molecule, depicted below. This glucose chain forms a ring in aqueous solutions, e. Polysaccharides: Starch, Glycogen, and Cellulose Glucose and fructose are examples of monosaccharides, meaning they consist of a single sugar unit, while sucrose is an example of a disaccharide.
Although glucose, galactose, and fructose all have the same chemical formula C 6 H 12 O 6 , they differ structurally and chemically and are known as isomers because of differing arrangements of atoms in the carbon chain. During this process, the hydroxyl group —OH of one monosaccharide combines with a hydrogen atom of another monosaccharide, releasing a molecule of water H 2 O and forming a covalent bond between atoms in the two sugar molecules.
Common disaccharides include lactose, maltose, and sucrose. 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 from 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. The chain may be branched or unbranched, and it may contain different types of monosaccharides.
Polysaccharides may be very large molecules. Starch, glycogen, cellulose, and chitin are examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of amylose and amylopectin both polymers of glucose. Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds. The starch that is consumed by animals is broken down into smaller molecules, such as glucose.
The cells can then absorb the glucose. 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 glucose levels decrease, glycogen is broken down to release glucose.
Cellulose is one of the most abundant natural biopolymers. The cell walls of plants are mostly made of cellulose, which provides structural support to the cell.
Wood and paper are mostly cellulosic in nature. Cellulose is made up of glucose monomers that are linked by bonds between particular carbon atoms in the glucose molecule.
Every other glucose monomer in cellulose is flipped over and packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. Cellulose passing through our digestive system is called dietary fiber.
While the glucose-glucose bonds in cellulose cannot be broken down by human digestive enzymes, herbivores such as cows, buffalos, and horses are able to digest grass that is rich in cellulose and use it as a food source. In these animals, certain species of bacteria reside in the rumen part of the digestive system of herbivores and secrete the enzyme cellulase.
The appendix also contains bacteria that break down 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.
Carbohydrates serve other functions in different animals. Arthropods, such as insects, spiders, and crabs, have an outer skeleton, called the exoskeleton, which protects their internal body parts.
This exoskeleton is made of the biological macromolecule chitin , which is a nitrogenous carbohydrate. It is made of repeating units of a modified sugar containing nitrogen. Thus, through differences in molecular structure, carbohydrates are able to serve the very different functions of energy storage starch and glycogen and structural support and protection cellulose and chitin.
Registered Dietitian: Obesity is a worldwide health concern, and many diseases, such as diabetes and heart disease, are becoming more prevalent because of obesity. This is one of the reasons why registered dietitians are increasingly sought after for advice.
Registered dietitians help plan food and nutrition programs for individuals in various settings. They often work with patients in health-care facilities, designing nutrition plans to prevent and treat diseases. For example, dietitians may teach a patient with diabetes how to manage blood-sugar levels by eating the correct types and amounts of carbohydrates. Dietitians may also work in nursing homes, schools, and private practices.
In addition, registered dietitians must complete a supervised internship program and pass a national exam. Those who pursue careers in dietetics take courses in nutrition, chemistry, biochemistry, biology, microbiology, and human physiology.
Dietitians must become experts in the chemistry and functions of food proteins, carbohydrates, and fats. The underground storage bulb of the camas flower shown below has been an important food source for many of the Indigenous peoples of Vancouver Island and throughout the western area of North America.
Camas bulbs are still eaten as a traditional food source and the preparation of the camas bulbs relates to this text section about carbohydrates. Most often plants create starch as the stored form of carbohydrate. Some plants, like camas create inulin. Inulin is used as dietary fibre however, it is not readily digested by humans. If you were to bite into a raw camas bulb it would taste bitter and has a gummy texture.
The method used by Indigenous peoples to make camas both digestible and tasty is to bake the bulbs slowly for a long period in an underground firepit covered with specific leaves and soil. The heat acts like our pancreatic amylase enzyme and breaks down the long chains of inulin into digestible mono and di-saccharides. Properly baked, the camas bulbs taste like a combination of baked pear and cooked fig. It is important to note that while the blue camas is a food source, it should not be confused with the white death camas, which is particularly toxic and deadly.
The flowers look different, but the bulbs look very similar. Lipids include a diverse group of compounds that are united by a common feature. This is because they are hydrocarbons that include only nonpolar carbon-carbon or carbon-hydrogen bonds.
Lipids perform many different functions in a cell. Cells store energy for long-term use in the form of lipids called fats.
Lipids also provide insulation from the environment for plants and animals. For example, they help keep aquatic birds and mammals dry because of their water-repelling nature. Lipids are also the building blocks of many hormones and are an important constituent of the plasma membrane. Lipids include fats, oils, waxes, phospholipids, and steroids. A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids.
Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl —OH groups. In a fat molecule, a fatty acid is attached to each of the three oxygen atoms in the —OH groups of the glycerol molecule with a covalent bond. During this covalent bond formation, three water molecules are released. The three fatty acids in the fat may be similar or dissimilar. It is transported around the bodies of plants as fuel and raw material for making other biological molecules.
For example, stored starch in the roots of trees is converted to sucrose and transported up the trunk to the buds in springtime. The buds begin to grow and make new leaves using the sucrose as fuel and raw material. Later in the year, the leaves will make sucrose by photosynthesis and send it down the trunk to the roots to be made into starch. In the case of some maple trees, the sap and its dissolved sucrose can be extracted from the trunk and made into maple syrup.
Starches are polymers of sugars, often glucose. Starch molecules are large, hundreds of carbons. They are used for storage of sugars. They are made of sugars and can be broken down into sugars again when needed. Plants store large amounts of starch, e. Animals store small amounts of starch, e. Like starches, cellulose is a polymer of glucose but the glucose monomers are connected with more chemical bonds than in starch.
This makes cellulose very strong and insoluble in water, unlike starch. This is good because plants use cellulose for structure. Wood contains cellulose as do the cotton fibers in your clothing. Paper is mostly cellulose. Lipids include fats and oils.
They are constructed of long chains of carbon and hydrogen called fatty acids. Foods like potatoes, corn, rice, and wheat are rich in starch.
Animals break the starches back down into glucose subunits and convert the glucose into glycogen for storage. Glycogen is a complex storage molecule made from glucose using insulin. Diabetics, who lack insulin, cannot make glycogen so they excrete excess sugar in their urine.
Glucose is broken down through a process called glycolysis lysis means splitting in order to release energy stored in the carbon-carbon bonds. These molecules contain the genetic code, which has all the information necessary to build the body.
The basic unit is called a nucleotide, which is composed of a sugar-phosphate backbone attached to one of four nitrogenous bases; cytosine, guanine, adenine or thymine. C joins to G, and G to C by three hydrogen bonds, indicated by the dotted lines. A joins to T and T to A by two hydrogen bonds. Note that the DNA molecule shown below is double stranded, and that the two strands run in opposite directions, denoted by the 3' and 5' ends.
While nucleic acids are important as information carrying molecules, they are not nutritionally important. The Molecules of Life Proteins Proteins are the primary building materials of the body.
Dehydration Synthesis and Hydrolysis: Proteins, fats, and carbohydrates all use these two common reactions involving water to assemble and disassemble the molecule.
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