University:
Kentucky State University
Course:
CHE 315 | Biochemistry
Academic year:

2023
Views:

311

Pages:

44
Author:

pravitate8aj11

Carbohydrates Summer 2020 What are they? Carbohydrates are polyhydroxy aldehydes or ketones Saccharide is another name for a carbohydrate Functions: (Structural & Functional) Source of energy (the quickest especially in aerobic metabolism (and anaerobic as well). Structure (cellulose in plants and chitin which forms the outside structure (exoskeleton) of insects) Building blocks Cellular recognition, like immune cells for example can recognize self/non-self cells using the sugars on the surface of cells. Important for signaling (outside to inside). Classification I By the number of sugars that constitute the molecule Monosaccharides, Disaccharides, Oligosaccharides, Polysaccharides *Mono: single Di: double Oligo: 3-10 Poly: > 10. Carbohydrates – natural forms Most carbohydrates are found naturally in bound form rather than as simple sugars Polysaccharides (starch, cellulose, inulin, gums, glycogen) Glycoproteins and proteoglycans (hormones, blood group substances, antibodies) Glycolipids (cerebrosides, gangliosides) Glycosides: these are sugars modified by methyl, ethyl or amino acids for example. Mucopolysaccharides (hyaluronic acid) Nucleic acids (DNA, RNA), like ribose and deoxyribose. Monosaccharides They are highly soluble! Basic chemical formula: (CH2O)n They contain two or more hydroxyl groups. The functional group (aldehyde group here) which includes the most oxidized carbon has to be ON TOP. Fisher projections or perspective structural formulas. *Groups that extend sideways actually go FORWARD. *Groups that are vertical go BACKWARD. Forward Backward Top (C1): Most highly oxidized C Classification 2 By the number of carbon atoms they contain. Triose Tetrose Pentose Hexose Heptose … MAINLY, monosacchari des exit as aldoses . Classification III By the functional group Aldoses You should memorize the structure (the exact positions & orientations of hydroxyl groups) for the four squared sugars in addition to the structure of Dglyceraldehyde. This is the simplest aldose (aldotriose). Notice the difference between (glucose and galactose), (glucose and mannose). Ketoses Notice that the ketone group is ALWAYS at carbon number 2. You should memorize the structure of fructose. Common Monosaccharides Glucose: Metabolism usually starts with glucose in terms of generation of energy. Mild sweet flavor Known as blood sugar Essential energy source Found in every disaccharide and polysaccharide Either in its form or as a modified sugar. Galactose: Hardly tastes sweet & rarely found naturally as a single sugar usually associated with proteins. Fructose: Sweetest sugar, found in fruits and honey Added to soft drinks, cereals, desserts Trioses What is a chiral carbon? A carbon that is connected to four different groups. Chiral carbon It doesn’t contain any chiral carbon. Note what a chiral carbon is…    Isomerism So basically, every atom is connected to the same group as the other molecule except that they are ORIENTED differently in space in each molecule. Isomers that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. Isomers Stereoisomers Enantiomers L-isomers D-isomers An isomer is a molecule with the same molecular formula as another molecule, but with a different chemical structure. Constitutional isomers Diastereomers Epimers Molecules with the same molecular formula, but have different bonding patterns and atomic organization. Isomers of glucose 2n (n is the number of chiral carbons in a sugar molecule) Search for: Glucose and it’s enantiomer. Galactose Mannose We use this equation to calculate the MAXIMUM number of isomers a molecule might have. Enantiomerism Isomers Stereoisomers Two stereoisomers that are mirror images of each other and are nonsuperimposable (not identical) so they cannot be put on top of each other and looking exactly the same. Enantiomers L-isomers D-isomers Constitutional isomers Diastereomers Epimers Sugar enantiomers (D- vs. L-) How would I know if a specific molecule has a mirror image molecule? If it contains a chiral carbon then it would have a mirror image. If the hydroxyl group is oriented to the right then it is know as a D-glyceraldehyde. If it is oriented to the Left then it is known as L-glyceraldehyde . D : dextro L: Levo . Every molecule has ONE enantiomer but it can have different isomers. Which one(s) is a chiral carbon? Isomerism Isomers Stereoisomers Enantiomers L-isomers D-isomers Constitutional isomers Two or more stereoisomers of a compound having different configurations Diastereomers at one or more (but not all) of the chiral carbons and are not mirror images of each other. Epimers Stereoisomers, but non-mirror images and non-superimposable, then…diastereomers OH H H OH Isomerism Isomers Stereoisomers Enantiomers L-isomers D-isomers Constitutional isomers Diastereomers Epimers Epimer refers to one of a pair of stereoisomers whereby two isomers differ in configuration at only one chiral carbons. Diastereomers that differ in the orientation of one chiral carbon…epimers Is L-glucose an epimer with D-mannose and D-galactose? Acetal/ketal vs. hemiacetal/hemiketal Hemiacetal and hemiketal: ether and alcohol on same carbon Acetal and ketal: two ethers on same carbon What is the difference between hemiacetal and hemiketal and the difference between acetal and ketal? Formation of a ring structure Anomers Anomers as Fischer projection Chain to ring Left-up, right-down Going down to your right Cyclic aldohexoses Cyclic ribofuranose Sugar acids (oxidation) Where is it oxidized? What does it form? Example 1 Example 2 Example 3 Note Oxidation of ketoses to carboxylic acids does not occur, but they can be oxidized because of formation of enediol form. Benedict’s test Oxidation of cyclic sugars (lactone) Tollen’s test Lactone An organic compound containing an ester group —OCO— as part of a ring. A more recent method for the detection of glucose, but not other reducing sugars, is based on the use of the enzyme glucose oxidase. • Vitamin C (ascorbic acid) is an unsaturated lactone. • Air oxidation of ascorbic acid, followed by hydrolysis of the ester bond, leads to loss of activity as a vitamin. • A lack of fresh food can cause vitamin C deficiencies, which, in turn, can lead to scurvy. Sugar alcohols (reduction) What does it form? Examples include sorbitol, mannitol, and xylitol, which are used to sweeten food products Deoxy sugars (reduced sugars) One or more hydroxyl groups are replaced by hydrogens. An example is 2deoxyribose, which is a constituent of DNA. Another one L-fucose (L-6-deoxygalactose) found in the carbohydrate portions of some glycoproteins Sugar esters (esterification) What is the reacting functional group? Where does it react? What are the end products? Where are they used? O-Glycosides What is the reacting functional group? Where does it react? What are the end products? Where are they used? N-glycosides What is the reacting functional group? Where does it react? What are the end products? Where are they used? Examples: nucleotides (DNA and RNA) Note Glycosides derived from furanoses are called furanosides, and those derived from pyranoses are called pyranosides, regardless if they are N- or Olinkded. Amino sugars What is the reacting functional group? Where does it react? What are the end products? Where are they used? Further modification by acetylation

Carbohydrates Lecture

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