Carbohydrates

What are carbohydrates? Carbohydrates are polyhydroxy aldehydes, ketones, or compounds that yield polyhydroxy aldehydes or ketones upon hydrolysis. Carbohydrates can be classified as monosaccharides or as polysaccharides. http://upload.wikimedia.org/wikipedia/commons/b/b0/Monosaccharide_Structure.png Polysaccharides http://image.tutorvista.com/content/cellular-macromolecules/polysaccharides-structure.jpeg

Carbohydrate Examples Rice Potatoes Bread Corn Candy Fruit

Monosaccharides Monosaccharides exist mostly as cyclic structures containing hemiacetal groups. Hemiacetal groups are capable of reducing oxidizing agents such as Benedict’s or Fehling’s reagent.

Polysaccharides Polysaccharides exist as cyclic structures containing functional groups such as hydroxyl, acetal, and hemiacetal groups. Most polysaccharides have two distinct ends. The end with the hemiacetal group is the “reducing” end while the one with the acetal group is the “nonreducing” end.

Non-reducing Polysaccharides Not all polysaccharides have a hemiacetal group on one of their terminal ends. For these polysaccharides, hydrolysis can be used to break down the glycosidic linkages to create reducing ends. This will result in a positive test for Benedict’s or Fehling’s reagent. This hydrolysis can be achieved through the use of a strong acid such as HCl or use of an enzyme.

Starch Starch will form an intense blue color when combined with iodine. This blue color is attributed to the straight chain component of starch (amylose). Amylopectin, the branched component of the starch molecule will form a purple color with iodine. When starch is fully broken down through hydrolyzation into small carbohydrate units, iodine will give neither a blue nor purple color. Because of this, iodine can be used to indicate when full hydrolysis of starch is complete.

Today we will… Investigate the reducing and nonreducing properties of carbohydrates in terms of their functional groups. We will look at: Aldoses Ketoses Hemiacetal functional groups

Different carbohydrates we will test for reducing or nonreducing capabilities…. Glucose Fructose Sucrose Lactose Starch

We will also… Hydrolyze sucrose (a nonreducing carbohydrate) with both an acid and a base. Hydrolyze starch with acid and note the speed at which it is able to break down the starch molecule. We will test the progress of the hydrolysis by using the iodine test.

Remember… Starch that is not fully broken down will yield a purple color. To find the point at which our starch hydrolysis is complete we must get a clear reaction to the iodine test.

Caution! We will use Fehling’s reagent today (not Benedict’s reagent). There is a waste container for Fehling’s reagent in the hood. Everything else can go down the drain.

Potential Health Concerns Inhalation: irritant, sneezing, runny nose, pneumonitis, ulceration, labored breathing, lung edema and perforation of the nasal septum Ingestion: gastrointestinal disturbances, nausea, vomiting, diarrhea, bloody stools, low blood pressure, thyroid hyperfunction, jaundice, abdominal pain, cathartic effects, coma, central nervous system depression, kidney and liver damage, burns of the mouth, throat and stomach, scarring of tissue, bleeding, circulatory collapse, clammy skin, weak and rapid pulse, shallow respirations, circulatory shock, death Skin contact: corrosion, redness, pain, burns, scarring, irritation, sensitization, itching eczema, dermatitis and allergic reaction Eye contact: burns, permanent vision impairment, blindness, redness, pain, irritation, conjunctivitis, ulceration and corneal abnormalities Mutagen, teratogen, tumorigen, carcinogen and reproductive effector