Introduction to the discussions about carbohydrates structure and metabolism Ferchmin 2016 Please, read very carefully the text below In (1) grammar and (2) high school, you have learned to read, write, the four math operations, rudiments of biology, and social sciences. In (3) college, you should have learned more of the above including chemistry and biological sciences. Necessarily it must be assumed that a PhD candidate has a certain degree of learning capacity, a boundless enthusiasm to learn and at least a minimum knowledge of mathematics, chemistry and biology. Graduate studies (4) for a PhD or MS in Biological Sciences must be oriented toward the development of the capacity for independent research and teaching. In other words, the student should learn how to solve problems. Perhaps you speculated what the (#) mean. They refer to steps in education. Graduate studies or quaternary education (4) is for the development of creative independent thinking not for learning more information that you may never use. Therefore, courses about general sciences are superfluous because whatever you learn will be forgotten during the first year. However, courses in the area of your specific interest are needed and could be offered by your mentor as an individualized seminar course or by other means. The PhD candidate should develop fundamental lab skills in the area of his/her interest. A program of seminars and courses appropriate for a students background and interests should be arranged through consultation between the student and the mentor. In view of the above considerations, there will be no lectures about structure and metabolism of carbohydrates. Instead there will be discussions about the regulation of the metabolism, analysis of the interaction between pathways, conceptual problem solving, and other amenities of biochemistry. To achieve this, students will have to read about the pathways before the discussion session and be ready to participate in the classroom. You could use the handouts from my Web Page or you could study from other sources. Open books and computer searches will be mandatory. Because of the discussion-oriented nature of these activities, your participation will be required. The collaboration of the students will have to include the shaping of the course by providing feedback to me. 1 Note I will appreciate if you bring to my attention any errors (not all, please) you may find in my handouts. Suggestions for improvement are always welcomed. The best way to communicate with me is at: For safety reasons I do not check I neither agree, disagree, acknowledge or check whatever is posted about me in2 THE STRUCTURE OF CARBOHYDRATES The objectives of this presentation is to motivate you to think molecular; to review concepts learned in organic chemistry and familiarize yourself with the carbohydrate molecules involved in metabolism. Summary of this presentation: 1) Definition of carbohydrate. 2) Asymmetric carbon, Fischer projection formulas. 3) D and L series. 4) Mutarotation, Haworth formulas and anomers. 5) Examples of monosaccharides. Fructose, mannose, galactose, deoxysugars, aminosugars, glucuronic and gluconic acids. 6) Glycosides and disaccharides. Lactose, maltose, isomaltose, cellobiose, sucrose 7) Homo- and heteropolysaccharides. Glycogen !!!! 8) Glycosaminoglycans (formerly called mucopolysaccharides). 3 Carbohydrates are polyalcohols of ketones or aldehydes and simple derivatives (like carboxylic acids or amino sugars), and polymers. Carbohydrates can be considered as 'carbon hydrates', the empirical formula is Cn(H 2 O)n. There is one water molecule per carbon atom. Carbohydrates are also called sugars or saccharides. The thousands of different carbohydrates found in nature are stereoisomers, derivatives or polymers of a rather small number of monosaccharides. For that reason, the concept of isomerism is important to understand carbohydrates. Functions of carbohydrates Energy Glucose is the circulating sugar in blood and the energy source for most organs. Glycogen is one of the most important energy stores. Oxidation of glucose to CO 2 and H 2 O is the central energy yielding process. Structural Polysaccharides are used as shock absorbers and lubricants in joints and as adhesives between cells. Signaling Sugars associated with proteins or lipids are involved in cell signaling. Sugars are involved in cell-cell interactions, immunological responses and determine the metabolic role of many proteins. 4 Stereoisomery of carbohydrates is produced by the asymmetric carbon. The asymmetric carbon is tetrahedral and has 4 substituents. These three pictures show molecules that are enantiomers or mirror images of each other 5 To make it easier to write Fischer made the Fischer convention: You must apply it to each and all the asymmetric carbons of a molecule. Or to make it simpler you may use the projection formula 6 The smallest sugars with an asymmetric carbons are shown below: Conceptually speaking D-glyceraldehyde originates the series of D-carbohydrates, and reciprocally L-glyceraldehyde the L series. 7 Aldoses are derivatives of glyceraldehyde 8 The asymmetric carbons in a hexose have to be viewed one by one. Glucose is a carbohydrate of 6 carbons 9 Asymmetric carbons rotate polarized light: Ordinary light vibrates in all possible planes. When ordinary light is filtered by certain crystals a single plane of polarized light is obtained. Polarized light traveling through a solution of an asymmetric compound, such as sugar, can rotate the plane of polarized light. The degree of rotation is directly proportional to the concentration of the asymmetric compound. Substances that rotate the plane of polarized light are called "optically active." Rotation to the left is indicated as l and to the right as d. Contrary to intuition the levo or dextro rotation provides no clue whether a sugar is from the L or D series. Confusion comes from the fact that D-glyceraldehyde was originally designated D because it rotated the polarization plane +13.5 degrees and L-glyceraldehyde because it rotated -13.8 degrees to the left. Each asymmetric carbon of a molecule has its own contribution to the total rotation of polarized light. 10 Ketoses are derivatives of dihydroxyacetone 11 MUTAROTATION 12 Pyranoses and furanoses The terms pyranose and furanose come from the similarity to pyran and furan to the rings formed by mutarotation. - D-Glucopyranose - D-Fructofuranose 13 -D-Glucopyranose -D-Glucofuranose -D-Glucofuranose -D-Glucopyranose 63% 36% 0.1%