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 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. The chain may be branched or unbranched, and it may contain different types of monosaccharides.
Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides. Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds.
The starch in the seeds provides food for the embryo as it germinates while the starch that is consumed by humans is broken down by enzymes into smaller molecules, such as maltose and glucose. The cells can then absorb the glucose. Glycogen is the storage form of glucose in humans and other vertebrates. It 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.
Margarine, some types of peanut butter, and shortening are examples of artificially hydrogenated trans -fats. Many fast food restaurants have recently eliminated the use of trans -fats, and U.
Essential fatty acids are fatty acids that are required but not synthesized by the human body. Consequently, they must be supplemented through the diet. Omega-3 fatty acids fall into this category and are one of only two known essential fatty acids for humans the other being omega-6 fatty acids. They are a type of polyunsaturated fat and are called omega-3 fatty acids because the third carbon from the end of the fatty acid participates in a double bond.
Salmon, trout, and tuna are good sources of omega-3 fatty acids. Omega-3 fatty acids are important in brain function and normal growth and development. They may also prevent heart disease and reduce the risk of cancer. Like carbohydrates, fats have received a lot of bad publicity.
However, fats do have important functions. Fats serve as long-term energy storage. They also provide insulation for the body. Phospholipids are the major constituent of the plasma membrane. Like fats, they are composed of fatty acid chains attached to a glycerol or similar backbone. Instead of three fatty acids attached, however, there are two fatty acids and the third carbon of the glycerol backbone is bound to a phosphate group.
The phosphate group is modified by the addition of an alcohol. A phospholipid has both hydrophobic and hydrophilic regions. The fatty acid chains are hydrophobic and exclude themselves from water, whereas the phosphate is hydrophilic and interacts with water. Cells are surrounded by a membrane, which has a bilayer of phospholipids. The fatty acids of phospholipids face inside, away from water, whereas the phosphate group can face either the outside environment or the inside of the cell, which are both aqueous.
Because fat is the most calorie dense food and having a storable, high calorie compact energy source would be important to survival. The nature of its fat also made it an important trade good. Like salmon, ooligan returns to its birth stream after years at sea.
Its arrival in the early spring made it the first fresh food of the year. As you learned above all fats are hydrophobic water hating. To isolate the fat, the fish is boiled and the floating fat skimmed off. Importantly it is a solid grease at room temperature. Because it is low in polyunsaturated fats which oxidize and spoil quickly it can be stored for later use and used as a trade item.
Its composition is said to make it as healthy as olive oil, or better as it has omega 3 fatty acids that reduce risk for diabetes and stroke. It also is rich in three fat soluble vitamins A, E and K. Unlike the phospholipids and fats discussed earlier, steroids have a ring structure.
Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail. Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol.
It is also the precursor of vitamins E and K. Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells.
Waxes are made up of a hydrocarbon chain with an alcohol —OH group and a fatty acid. Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out. Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes.
Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly.
They are all, however, polymers of amino acids, arranged in a linear sequence. The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order.
For example, proteins can function as enzymes or hormones. Enzymes , which are produced by living cells, are catalysts in biochemical reactions like digestion and are usually proteins. Each enzyme is specific for the substrate a reactant that binds to an enzyme upon which it acts. Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds. An example of an enzyme is salivary amylase, which breaks down amylose, a component of starch.
Hormones are chemical signaling molecules, usually proteins or steroids, secreted by an endocrine gland or group of endocrine cells that act to control or regulate specific physiological processes, including growth, development, metabolism, and reproduction. For example, insulin is a protein hormone that maintains blood glucose levels. Proteins have different shapes and molecular weights; some proteins are globular in shape whereas others are fibrous in nature.
For example, hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein. Protein shape is critical to its function. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation to be discussed in more detail later. All proteins are made up of different arrangements of the same 20 kinds of amino acids. Amino acids are the monomers that make up proteins.
Each amino acid has the same fundamental structure, which consists of a central carbon atom bonded to an amino group —NH 2 , a carboxyl group —COOH , and a hydrogen atom.
Every amino acid also has another variable atom or group of atoms bonded to the central carbon atom known as the R group. The R group is the only difference in structure between the 20 amino acids; otherwise, the amino acids are identical. The chemical nature of the R group determines the chemical nature of the amino acid within its protein that is, whether it is acidic, basic, polar, or nonpolar.
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. 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.
Since carbohydrates are an important part of the human nutrition, eliminating them from the diet is not the best way to lose weight. Key Terms carbohydrate : A sugar, starch, or cellulose that is a food source of energy for an animal or plant; a saccharide. ATP is the abbreviation for adenosine triphosphate. Licenses and Attributions. Figure Glucose and galactose are aldoses. Fructose is a ketose. Glycogen and starch are polysaccharides.
They are the storage form of glucose. Glycogen is stored in animals in the liver and in muscle cells, whereas starch is stored in the roots, seeds, and leaves of plants. Starch has two different forms, one unbranched amylose and one branched amylopectin , whereas glycogen is a single type of a highly branched molecule.
Herbivores such as cows, koalas, and buffalos are able to digest grass that is rich in cellulose and use it as a food source because bacteria and protists in their digestive systems, especially in the rumen, secrete the enzyme cellulase.
Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal.
Draw the ketose and aldose forms of a monosaccharide with the chemical formula C 3 H 6 O 3. How is the structure of the monosaccharide changed from one form to the other in the human body? The human body switches carbohydrates between their aldose and ketose forms using a family of enzymes called isomerases.
The ketose triose is called dihydroxyacetone, and has the oxygen double-bonded to the center carbon:. The aldose is called glyceraldehyde, and can have the oxygen double-bonded to the first or third carbon of the molecule:. Increase Font Size. Biology Go to home Biological Macromolecules 4.
Previous: Synthesis of Biological Macromolecules. Next: Lipids. Learning Objectives By the end of this section, you will be able to do the following: Discuss the role of carbohydrates in cells and in the extracellular materials of animals and plants Explain carbohydrate classifications List common monosaccharides, disaccharides, and polysaccharides.
Molecular Structures The stoichiometric formula CH 2 O n , where n is the number of carbons in the molecule represents carbohydrates. Scientists classify monosaccharides 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. Art Connection. 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 atom arrangement.
Five and six carbon monosaccharides exist in equilibrium between linear and ring forms. Fructose and ribose also form rings, although they form five-membered rings as opposed to the six-membered ring of glucose.
Sucrose forms when a glucose monomer and a fructose monomer join 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 forms between carbon 1 in glucose and carbon 2 in fructose. Common disaccharides include maltose grain sugar , lactose milk sugar , and sucrose table sugar.
Amylose and amylopectin are two different starch forms. Because of the way the subunits are joined, the glucose chains have a helical structure.
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