MCDB 310 1st EditionExam # 2 Study Guide Lectures: 8-14Lecture 8 (February 5, 2015)I. Chapter 7: Carbohydrates - Molecules for structure and energya. Carbohydrate classes: number of subunits, Monosaccharides vs Oligosaccharidesi. Monosaccharides:1. Sugar means “Monomer” - it is the building block2. Sugars tend to be aldehydes and ketones with two or morehydroxyl groups. The carbons to which these are attachedare chiral centers 3. D-Glucose (memorize this structure and be able to numberthe carbons) is the most common sugar. It is also calledDextrose.4. Names end in -oseii. Oligosaccharides & polysaccharides: short chains of sugars joined with glycosidic linkages. Disaccharides are the most common; sucrose is the most common of these disaccharides. 1. Oligosaccharides are less than 20 subunits (usually)2. Polysaccharides are more than 20 subunits, but can be up to thousands. 3. Some chains are linear (line up) and some are branched (don’t line up so nicely)a. Differences in bonds cause differences in function. For example, both starch and cellulose are polymers of glucose, but they differ greatly in structure and therefore function. b. Two Families of Monosaccharidesi. Mostly unbranched carbon chains (open chain or cyclic) with single bonds. This provides flexibility and rotation.ii. Aldose: carbonyl carbon is at one end (aldehyde)iii. Ketose: carbonyl carbon is anywhere but an end (ketone)iv. See the examples below: v.Can name sugars based on how many carbons are present 1. Example: three carbons —> triosevi. Can also name them based on aldose or ketose1. Example: aldotriose (combination of two naming methods)vii. Usually doesn’t get any more complex than 5 or 6 membered rings in cyclic saccharides1. 4 membered rings have steric problems 2. Some 7/8 membered ringsc. Monosaccharides have asymmetric centersi. Causes stereoisomers (remember: 2^n, when n isthe number of asymmetrical carbons) ii. Based on the configuration of the chiral center mostdistant from the carbonyl carboniii. Glyceraldehyde is the standard for which Dstereoisomers are identified. All other rotations oflight are then classified as L stereoisomers.d. Remember: Carbons are numbered started at the carbonyl carbon ende. Epimers: isomers that differ only in rotation about a single carboni. Example: D-glucose and D-mannose (only differ with a rotation about carbon2) f. Some common Monosaccharides are CYCLICi. 5 or more carbons tend to be cyclicii. Carbonyl carbon is bonded to a hydroxyl oxygeniii. Contain an additional asymmetric carbon, so they are stereoisomers (continue adding different R groups)iv.Example: D-glucose makes an intramolecular hemiacetal1. Two different molecules are produced based on the configuration at one asymmetrical carbon2. This matters because only one may fit in an active site in an enzyme3. This is the reason D-Glucose is the sugar predominant in biology —> it fits best into active sites of enzymes4. In comparing the alpha and beta configurations:a. Alpha form: oxygen is opposite from oxygen inhydroxyl group b. Beta: oxygen is next to the oxygen in thehydroxylc. These matter for making glycosidic linkages v. Aldohexoses exist as 5-membered and 6-membered rings (depending on how the nucleophilic attack happens) See the figure to the right1. The names come from what type of organic ring they come from (ie - pyran and furan)g. Monosaccharides can be reducing agentsi. The end of the sugar that undergoes the oxidation-reduction is called the reducing endii. Only reducing sugars can have a reducing endiii. The reducing end and non-reducing end of the sugar have very different functions (non-reducing end is where more carbons are added)iv. Oxidation of carbons leads to biologically important compounds1. In some sugars, hydroxyl is replaced with an amino, alcohol, etc.2. Carbonyl carbon can be oxidized to produce an aldonic acid (ie-gluconic acid)3. Carbon farthest from carbonyl can be oxidized to produce a Uronic acid (glucuronic acid)h. Carbohydrates in Diseasei. Sleeping sickness (trypanosomiasis - worms in the blood)1. It is debilitating and often fatal2. It is passed to humans by an insect bite and can pervade nearly all organs3. They are difficult to combat because the antibodies are useless4. The sole food source of Trypanosoma b. is blood glucose5. If you can stop the worms from metabolizing glucose (by adding an enzyme), then the disease will stop spreadingi. Disaccharides: monosaccharides joined by o-glycosidic bonds (because of the oxygen in the bond) i. Hydroxyl on one sugar plus anomeric carbon of theother sugar ii. The hemiacetal binds with the alcohol on another toproduce and acetaliii. The new terminus becomes the new hemiacetal(reducing end)iv. Water is also producedv. The reducing end of the sugar is the end with the free anomeric carbonvi. Anomers differ only in their rotation about hemiacetal or hemiketal carbon1. Hemiacetal or carbonyl carbons are anomeric (chiral) carbonsvii. Naming:1. Single-headed arrow shows which two carbons are coming together in the condensation reaction2. -syl at end of name: every monosaccharide before the last one in the chain3. -ose at end of name: the final monosaccharide in the chain4. Also need alpha or beta in front of the name5. Notice the curve between the H and O —> going downward it tells usabout the 3D structure (has to do with alpha vs. beta)a. If alpha: elbow curves down b. If beta: elbow curves upviii. Naming exceptions (see figure): 1. Non-reducing disaccharides are calledglycosides2. The joined positions are anomeric carbons3. They are represented with a DOUBLEHEADED ARROW (connection betweenanomeric carbons)4. By convention, use the combination or up/down curves for glycosidiclinkage between two anomeric carbonsj. Polysaccharides: glycansi. Have varying degrees of chain length, branching, and types of bondsii. Homopolysaccharides: structural elements and fuels, made up of all the same monosaccharides1. These are still linked with O-glycosidic linkages2. When branched, have possible different linkagesiii. Heteropolysaccharides: extracellular support in all kingdoms, made up of different monosaccharidesiv. Starch and Glycogen: stored fuels1. If you want to store carbs, you want them to be exceedingly stable (almost chemically inert), so that they can be put to use again2. Polymers of glucose that occur in nature as large aggregate (grains and granules)a. In plants: found in chloroplastsb. In animals: usually in