5.2

• Animals store excess glucose molecules in various ways.
• A carbohydrate is an organic compound made up of sugar molecules.
• Sugars contain the elements carbon, hydrogen, and oxygen in the ratio of 1 carbon: 2 hydrogen: 1 oxygen.
• The molecular formula of any carbohydrate is a multiple of the basic formula CH 2 O.
• At the core of most sugar molecules found in nature are carbon skeletons that have a ring shape.
• Monosaccharides are simple sugars that contain just one sugar unit and are called monosaccharides (mahn oh SAK uh rydz).
• Glucose, fructose, and galactose are examples of monosaccharides.
• One or more of these simple sugars are found in many sweet things you eat.
• Honey, for example, contains both glucose and fructose.
• Glucose exists in both straight-chain and ring-shaped forms.
• Figure 5-6 shows the complete molecular structure of glucose in its ring form, as well as a simplified diagram that shows only its core ring.
• This book will use the simplified representation of sugars in most diagrams.
• Sugar molecules, particularly glucose, are the main fuel supply for cellular work.
• Cells break down glucose molecules and extract their stored energy.
• Starch is a polysaccharide found in plant cells that consists entirely of glucose monomers.
• Potatoes, rice, and corn are examples of foods rich in starch.
• Starch chains serve as sugar stockpiles, providing energy for the plant and raw material for building other molecules.
• Glycogen, cellulose, and starch are three types of polysaccharides found in food.
• Animal cells do not contain starch.
• Polysaccharides are long polymer chains made up of simple sugar monomers, also known as complex carbohydrates.
• Sucrose is also found in maple syrup and table sugar.
• Glucose molecules that are not used immediately by cells are usually incorporated into larger carbohydrates, or they may be used to make fat molecules.
• The most common disaccharide is sucrose, which consists of a glucose molecule linked to a fructose molecule.
• Inside a plant cell, such as a potato cell, starch chains branch and coil up like the loops of a telephone cord.
• Disaccharides are constructed using the dehydration reaction, linking two monosaccharides together.
• Sucrose is a major carbohydrate in plant sap, and it nourishes all the parts of the plant.
• Cells use the carbon skeletons of monosaccharides as raw material for manufacturing other kinds of organic molecules.
• Though all three polymers are composed of the same monomer, glucose, the way the glucose monomers link together is different for each.
• When plants break down starch molecules, the stored glucose becomes available.
• Humans and most other animals are also able to use plant starch as food by breaking it down within their digestive systems.
• A monosaccharide is a simple sugar, while a disaccharide is a compound sugar.
• Most animals, including people, cannot digest cellulose because they lack the molecule necessary to break the bonds between the glucose monomers in cellulose.
• Cellulose and some forms of starch are still hydrophilic, which is why cotton bath towels can absorb so much water.
• Cellulose and some forms of starch, however, are such large molecules that they do not dissolve in water.
• Some organisms, such as cows and termites, can derive nutrition from cellulose.
• Cellulose from plant foods, commonly referred to as "fiber," passes unchanged through your digestive system.
• Multiple cellulose chains are linked together with hydrogen bonds, forming cable-like fibers in the tough walls that enclose plant cells, such as the cells of broccoli stems.
• A glycogen polymer is more highly branched than a starch polymer.
• Microorganisms that inhabit their digestive tracts break down the cellulose, making glucose available to the cow or termite.
• Some polysaccharides in plants, such as cellulose, serve as building materials.