BIO 205Exam # 3 Study Guide: Chapters 16-22Part III: Other Structures Chapter 16: Carbohydrate Monomers- Aldoses end in an aldehyde group while ketoses contain a ketone group. - The C=O group of an aldose always occurs at carbon 1 and the C=O group of a ketose always occurs at carbon 2.- Enantiomers are mirror images, meaning that every chiral center has been switched between the two molecules. Epimers are molecules that differ at only one chiral center. Diastereomers are molecules that differ by more than one but not all chiral centers.- When forming a ring, the hydroxyl group on the highest numbered chiral center on either an aldose or a ketose will attack the partially positive carbon of the carbonyl group. The original carbonyl oxygen will then change to a hydroxyl oxygen, and the original hydroxyl oxygen will become part of the ring structure. - Depending on the position of the carbonyl group, two cyclic forms can be produced. The alpha form has the hydroxyl group formed from the original C=O group pointing down in relation to the CH2OH group (highest numbered carbon in linear form) that is always pointed up. The beta form has this hydroxyl group pointing up. These two forms are called anomers, and they can be interconverted, which is called mutarotation. o Alpha = a = away (antagonistic) o Beta = b = buddies- Furanose = 5-membered ring and pyranose = 6-membered ring.- 5 and 6-membered rings are most common for cyclic carbohydrates because they are able to adopt bonding angles closest to the 109° found in a tetrahedral configuration. - The carbon atom that is the C of the C=O group in the linear form is called the anomeric carbon. - The boat and chair conformation of 6-membered rings give the most stable angles. In the chair form, the most stable form is when all the bulky groups are in the equatorial positions because they all point away from each other. - β-D-ribose is the carbohydrate that is incorporated into nucleic acids. Chapter 17: Sugars – Dimers and Polymers- The most chemically reactive site on a carbohydrate is the carbon of the carbonyl group in the linear form of an aldose. This is called the reducing end of a sugar because it is oxidized to a carboxylic acid. - Monosaccharides combine by a condensation reaction where two alcohol groups form an ether bond, which is called a glycosidic bond.- In the cyclic form, a carbohydrate can only be reactive at the anomeric carbon if there is a free OH group. Some dimers will have a reactive end and others will not depending on which carbon they bond to. Maltose has a reactive end because its reactive anomeric carbon #1 of the first glucose forms a glycosidic bond with carbon #4 of the second glucose, leaving carbon #1 on the second glucose molecule free to react. Sucrose on the other hand does not have a reactive end because both the reactive ends of glucose and fructose are used to form the glycosidic bond. (Note, in ketoses, the reactive anomeric carbon will be carbon #2)- When naming dimers, their abbreviations reflect the nature of their bonding. For example, lactose is abbreviated Gal(β1-4)Glc because the beta-anomeric carbon (#1) of galactose bonds to carbon #4 of glucose. Since carbon #1 of glucose is left unreacted, it is free to mutarotate between α and β, so its form is not specified in the abbreviation. This is not true in the abbreviation of sucrose because both of the reactive ends of glucose and fructose are used to make the glycosidic bond, so both anomeric carbons are locked in their α/β forms. Sucrose can be abbreviated Glc(α1-β2)Fru or Fru(β2-α1)Glc (#2 is used because fructose is a ketose). Since sucrose no longer has a reactive end, it doesn’t matter which one is listed first. - Starch (and glycogen) is a homopolymer of glucose formed from 1  4 glycosidic linkages between alpha anomers. Another name for starch is α-Amylose. A long chain of starch/glycogen tends to form into a helix and is digestible in animals. - Starch and glycogen can also have branches by forming 1  6 glycosidic linkages with other alpha anomer chains. - Cellulose is also a homopolymer of glucose with 1  4 glycosidic linkages but with beta anomers. Cellulose tends to form into sheets that can hydrogen bond with other sheets to form a very rigid structure that cannot be digested by most animals, except for ruminants (animals with a rumen  cows) and termites because they have a bacteria that can digest the β1-4 bonds. - Chitin is a homopolymer of glucose units that have an acetylated amine group at C2 (GlcNAc) with β1-4 glycosidic linkages. - The cell wall of a bacteria is made of peptidoglycan. When stained, bacteria that have their peptidoglycan layer exposed will react with the stain and are called Gram-positive. Bacteria that have their peptidoglycan layer covered with another layer will not stain andare called Gram-negative. Peptidoglycan is a unique molecule because it is one of the few biological molecules that contains a D-amino acid (D-ala). Furthermore, the largest bacterial molecule is the cell wall, having a molecular weight of 4,500,000,000 grams permole. Peptidoglycan is a copolymer of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid β anomers. - Hyaluronic acid is a copolymer of N-acetylglucosamine and glucuronic acid. - Glycoproteins are proteins which have some carbohydrates attached to them. They are usually found on the outer surface of the cell membrane. The short branched sugar chains attached to the protein are called oligosaccharides and are attached by forming a covalent bond with the O of serine’s and threonine’s side chains (O linked) or with the N of asparginine’s side chain (N linked).- Oligosaccharides are first formed by enzymes in the cytoplasm, which attach the short sugar chains to the end of a very long lipid called dolichol. This lipids spans the ER membrane, so when it flips its orientation, the oligosaccharides is now inside the ER. It isthen separated from dolichol, attached to the newly synthesized protein, and sent by theER to the cell membrane. - Short oligosaccharide sequences correspond to the different blood types (A, B, and O). The O antigen sequence is found in all humans. The A antigen has an extra GalNac and the B antigen has an extra Gal. AB blood type has all three forms on its lipids and proteins that are in contact with the bloodstream. Another blood antigen is the Rh factor. If you have the