Unit 7 Carbohydrates Chapter 16

What are Carbohydrates? Sugars and starches that are found in such foods as bread, pasta and rice. The term “carbohydrate” comes from the observation that when you heat sugar, you get carbon and water. Comes from the word “saccharides” (saccharo is Greek for “sugar”) Formed from aldehydes and ketones.

Formation of Carbohydrates Form from the reaction of alcohols with aldehydes or ketones. They form hemiacetals (if aldehyde) or hemiketal (if ketone) These are called polyhydroxy because they have multiple hydroxyl groups

1. Monosaccharides contain a single polyhydroxy aldehyde or ketone unit (e.g., glucose, fructose). 2. Disaccharides consist of two monosaccharide units linked together by a covalent bond (e.g., sucrose). 3 Categories of Carbs

Polysaccharides contain very long chains of hundreds or thousands of monosaccharide units, which may be either in straight or branched chains (e.g., cellulose, glycogen, starch).

Simple Carbs: Monosaccharides Composed of carbon, hydrogen and oxygen Have the general formula (CH 2 O) n, where n is any number between 3 & 7. Not all follow this formula. Can be named by the functional groups attached (aldehyde or ketone) OR by the number of carbons in the main skeleton.

Isomers Monosaccharides can exist in many isomeric forms. D- and L- are used as prefixes in the name to identify that it is one of 2 possible stereoisomers. Stereoisomers have the same formula and the same bonding, but differ in spatial arrangement.

Isomers Stereoisomers are mirror images of one another, but means if you superimpose one onto the other, they will not match up.

Isomers 2 stereoisomers that are nonsuperimposable mirror images are called enantiomers. Molecules that can exist in enantiomeric forms are called chiral molecules. A carbon that has four different groups bonded to it is called a chiral carbon.

Cyclic vs. Straight Chained The straight chain form of monosaccharides are less common than cyclic forms. Cyclic forms exist under specific physiological conditions. In the case of glucose the C-1 would react with the OH group on the C-5 creating a ring.

Cyclic vs. Straight Chained In slide #3 of this ppt, we learned that when aldehydes react with alcohols you get a hemiacetal. In this case, when the aldehyde portion of glucose reacts with the OH group it creates an intermolecular hemiacetal. These create alpha and beta isomers.

Chirality: Alpha vs. Beta Glucose Both are chair formations The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal projection. The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection.

Alpha vs. Beta Glucose The alpha and beta label is not applied to any other carbon - only the anomeric carbon. The anomeric carbon is the center of a hemiacetal functional group. A carbon that has both an ether oxygen and an alcohol group is a hemiacetal.

How do complex sugars form from simple sugars? A dehydration synthesis reaction occurs. (Water is removed) A glycosidic bond is formed between each single sugar unit connecting the oxygen atoms. WLNhMtM WLNhMtM

Properties & Functions of Monosaccharides Glucose: Common names (dextrose, grape sugar and blood sugar) Broken down by the body through glycolysis to produce energy. Glucose levels in the body are important for normal function. (should be mg/100mL) Glucose levels rise after eating and return to normal after a couple of hours. When levels get too low lightheadedness and shakiness occurs.

Properties & Functions of Monosaccharides Fructose: Also called levulose and fruit sugar. It is the sweetest of all sugars. Naturally found in honey, fruits, berries and root vegetables. Commercially added to foods and drinks for enhancing taste. The form of fructose comes from corn, sugar beets and sugar cane. Ketone sugar, meaning it has a ketone group instead of an aldehyde. Has 6 carbons.

Properties & Functions of Monosaccharides Galactose: Part of biological systems as a component of lactose (milk sugar) Found in the milk of most mammals. Beta-D-Galactose and Beta-D-N- acetylgalactosamine are part of the blood group antigens. Contains an aldehyde group. A small amount creates a lot of energy.

Properties & Functions of Monosaccharides Ribose: A component of RNA 5 carbon atoms Used to transfer energy rather that create it Helps translate genes into proteins

Properties & Functions of Polysaccharides Starch: Composed of the 2 glucose polymers amylose and amylopectin Produced by green plants as an energy source Pure starch is white, tasteless and odorless The most common carb in the human diet Found in potatoes, wheat, corn and rice The largest non-food use of starch is as an adhesive in the papermaking process

Properties & Functions of Polysaccharides Glycogen: Major glucose storage molecule in animals Stored in the liver and skeletal muscle Similar structure to starch, but more branched & compact Used as an energy reserve Only the glycogen stored in the liver is accessible to other organs Glycogen is stored in the uterus during pregnancy to give nourishment to the embryo

Properties & Functions of Polysaccharides Cellulose: The most abundant polysaccharide Contains about 3000 glucose units (the largest cellulose molecule contains 26,000 glucose units) Structural component of the plant cell wall Cannot be digested by the body (because we cannot synthesize the enzyme cellulase which can break up the bonds of the polymer

Starch vs. Cellulose Starches can be digested by animals but cellulose cannot. Most animals that ingest grass or wood have special microorganisms living in their gut that digest the cellulose and the animals in turn absorb the breakdown product that is produced. CORN IN YOUR POOP!!