The shine and stiffness imparted to clothing by starch are due to the presence of dextrins formed when clothing is ironed. Because of their characteristic stickiness with wetting, dextrins are used as adhesives on stamps, envelopes, and labels; as binders to hold pills and tablets together; and as pastes. Dextrins are more easily digested than starch and are therefore used extensively in the commercial preparation of infant foods.
The complete hydrolysis of starch yields, in successive stages, glucose:. In the human body, several enzymes known collectively as amylases degrade starch sequentially into usable glucose units. Glycogen is the energy reserve carbohydrate of animals. Like starch in plants, glycogen is found as granules in liver and muscle cells. When fasting, animals draw on these glycogen reserves during the first day without food to obtain the glucose needed to maintain metabolic balance.
Although the percentage of glycogen by weight is higher in the liver, the much greater mass of skeletal muscle stores a greater total amount of glycogen. Glycogen is structurally quite similar to amylopectin, although glycogen is more highly branched 8—12 glucose units between branches and the branches are shorter.
When treated with iodine, glycogen gives a reddish brown color. Glucose can therefore also be called a monomer of protein. The amino acids form chains as a primary structure, and additional secondary forms occur with hydrogen bonds leading to alpha helices and beta pleated sheets. Folding of amino acids leads to active proteins in the tertiary structure. Additional folding and bending yields stable, complex quaternary structures such as collagen.
Collagen provides structural foundations for animals. The protein keratin provides animals with skin and hair and feathers. Proteins also serve as catalysts for reactions in living organisms; these are called enzymes. Proteins serve as communicators and movers of material between cells. For example, the protein actin plays the role of transporter for most organisms. The varying three-dimensional structures of proteins lead to their respective functions. Changing the protein structure leads directly to a change in protein function.
Nucleotides serve as the blueprint for the construction of amino acids, which in turn comprise proteins. Nucleotides store information and transfer energy for organisms.
Nucleotides are the monomers of natural, linear polymer nucleic acids such as deoxyribonucleic acid DNA and ribonucleic acid RNA. Nucleotide monomers are made of a five-carbon sugar, a phosphate and a nitrogenous base. Bases include adenine and guanine, which are derived from purine; and cytosine and thymine for DNA or uracil for RNA , derived from pyrimidine. The combined sugar and nitrogenous base yield different functions.
Nucleotides form the basis for many molecules needed for life. One example is adenosine triphosphate ATP , the chief delivery system of energy for organisms. Adenine, ribose and three phosphate groups make up ATP molecules. Phosphodiester linkages connect the sugars of nucleic acids together.
These linkages possess negative charges and yield a stable macromolecule for storing genetic information.
RNA, which contains the sugar ribose and adenine, guanine, cytosine and uracil, works in various methods inside cells. RNA exists in a single-helix form. DNA is the more stable molecule, forming a double helix configuration, and is therefore the prevalent polynucleotide for cells.
DNA contains the sugar deoxyribose and the four nitrogenous bases adenine, guanine, cytosine and thymine, which make up the nucleotide base of the molecule. The long length and stability of DNA allows for storage of tremendous amounts of information. Meanwhile, the rest of us will sit at the sidewalk restaurant, eating our spaghetti, and enjoying watching other people work hard. Many simple sugars can combine by repeated condensation reactions until a very large molecule is formed.
A polysaccharide is a complex carbohydrate polymer formed from the linkage of many monosaccharide monomers. One of the best known polysaccharides is starch, the main form of energy storage in plants. Starch is a staple in most human diets.
Foods such as corn, potatoes, rice, and wheat have high starch contents. Starch is made of glucose monomers and occurs in both straight-chain and branched forms.
Amylose is the straight-chain form, and consists of hundreds of linked glucose molecules. 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 to the cholesterol in the small intestine, then attaches to the cholesterol and prevents the cholesterol particles from entering the bloodstream, and 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 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. 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 of 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. Figure What kind of sugars are these, aldose or ketose? Skip to main content.
Biological Macromolecules. Search for:. Molecular Structures Carbohydrates can be represented by the stoichiometric formula CH 2 O n , where n is the number of carbons in the molecule.
Monosaccharides are classified based on the position of their carbonyl group and the number of carbons in the backbone. Aldoses have a carbonyl group indicated in green at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain. Trioses, pentoses, and hexoses have three, five, and six carbon backbones, respectively. Glucose, galactose, and fructose are all hexoses. They are structural isomers, meaning they have the same chemical formula C 6 H 12 O 6 but a different arrangement of atoms.
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