008_C1080_Carbohydrates_CH7(CH17)_Part I.pptx

CARBOHYDRATES CHAPTER 7 PART 1 T.TERPSTRA 24-7-10  IMPORTANT FUNCTIONS OF CARBOHYDRATES > To provide energy through their oxidation > To supply carbon for the synthesis of cell components > To serve as a stored form of chemical energy > To form a part of the...

CARBOHYDRATES CHAPTER 7 PART 1 T.TERPSTRA 24-7-10  IMPORTANT FUNCTIONS OF CARBOHYDRATES > To provide energy through their oxidation > To supply carbon for the synthesis of cell components > To serve as a stored form of chemical energy > To form a part of the structural elements of some cells and tissues Biomolecule – a general term referring to organic compounds essential to life Biochemistry – a study of the compounds and processes associated with living organisms  CARBOHYDRATES  Carbohydrates are polyhydroxy aldehydes or ketones or substances that yield such compounds upon hydrolysis. Example: Is Ribose Organic? What Functional Groups?  CLASSIFICATION OF CARBOHYDRATES  Carbohydrates are classified according to size: > Monosaccharide - a single polyhydroxy aldehyde or ketone unit > Disaccharide - composed of two monosaccharide units > Polysaccharide - very long chains of linked monosaccharide units  STEREOCHEMISTRY Stereoisomers - Compounds with same structural formula but different spatial arrangements of atoms Enantiomers- Stereoisomers that are mirror images - Non-superimposable - Chiral Diastereomers - Stereoisomers that are non-mirror images - Nonsuperimposable - Opposite configurations at some chirality centers  STEREOCHEMISTRY > Many carbohydrates exist as Enantiomers  CHIRALITY  An object or a system is chiral if it is distinguishable from its mirror image  A Chiral object cannot be superimposed on its mirror image  A Chiral Carbon is one that has four different groups attached to it  If any two groups are identical, the carbon is not chiral (Achiral) Chiral Achiral CHIRALITY  CHIRAL COMPOUNDS Chiral Achiral  Glucose How many chiral carbons in glucose? CHIRAL CARBONS OF GLUCOSE Chiral Carbons = 4 (C2,C3,C4,C5)  CHIRALITY > The presence of a single chiral carbon gives rise to stereoisomerism > If a carbon atom is attached to four different groups, it is chiral > If any two groups are identical, it is not chiral  CHIRALITY > Compounds can have more than one chiral carbon > The maximum number of stereoisomers is 2n where n= number of chiral carbon atoms > Therefore, this compound with two chiral carbon atoms has 2 2 or 4 stereoisomers BACK TO GLUCOSE… How many stereoisomers? 24 = 16 Stereoisomers  FISCHER PROJECTIONS > Fischer Projections depict three-dimensional shapes for chiral molecules > The chiral carbon represented by the intersection of two lines > Fischer Projections of carbohydrates have the carbonyl (C=O) group at the top (It is projecting away from the viewer behind the plane in which it is drawn) > The two horizontal bonds are coming toward the viewer out of the plane in which they are drawn > The bottom carbon group is projecting away from the viewer  D AND L ENANTIOMERS > The hydroxyl group on the chiral carbon farthest from the C=O group determines whether the carbohydrate is : D -OH on Right or L -OH on Left  Glucose D-Glucose L-Glucose Enantiomers  D AND L ENANTIOMERS > The physical properties of D and L enantiomers are generally the same > The EXCEPTION- the way solutions of the two compounds affect polarized light that is passed through them > Light is polarized by passing it through a special polarizing lens > When polarized light is passed through a solution of one enantiomer, the plane of polarization of the light is rotated to either the right or the left when viewed by looking toward the source of the light > D and L enantiomers rotate polarized light in equal, but opposite directions ENANTIOMER PROPERTIES Specific Rotation [α] - is a fundamental property of chiral substances that is expressed as the angle to which the material causes polarized light to rotate at a particular temperature, wavelength and concentration  ENANTIOMER PROPERTIES Optical Activity - The property of rotating the plane of polarized light - Measurements of optical activity are useful for differentiating between enantiomers > Levorotatory - The enantiomer that rotates polarized light to the left (-) Enantiomer > Dextrorotatory - The enantiomer that rotates polarized light to the right (+) Enantiomer *** Note: The D and L designations previously discussed DO NOT represent Dextrorotatory and Levorotatory Racemic Mixture - Composed of dextrorotatory and levorotatory forms of a compound in equal proportion  WHY IS THIS IMPORTANT?? > In some instances only the D or L enantiomers are found in nature > They are rarely found together in the same biological system > Important to understand this concept because: - Carbohydrates and amino acids are chiral - Humans can only metabolize the D-isomers of monosaccharides - Most animals are only able to utilize the L-isomer of amino acids  MESO COMPOUNDS A Meso compound is > A molecule with multiple chiral centers that is superimposable on its mirror image - Internal line of symmetry > Must have a minimum of two chiral carbons, with at least one on each side of the internal mirror plane  MESO COMPOUNDS > Since meso compounds are superimposable on their mirror images, they are considered achiral (chiral molecules, on the other hand, are not superimposable on their mirror images) > A meso compound is achiral so cannot have an enantiomer - When a molecule is superimposable on its mirror image, then that molecule and the mirror image are merely the same molecule > Meso compounds are optically inactive RECAP!!  STEREOISOMERS Stereoisomers > Compounds with same structural formula but different spatial arrangements of atoms Enantiomers > Stereoisomers that are nonsuperimposable mirror images > Opposite configurations at all chirality centers Diastereomers > Stereoisomers that are nonsuperimposable non-mirror images > Opposite configurations at some chirality centers  CHIRALITY > A Chiral object cannot be superimposed on its mirror image > A Chiral Carbon is one that has four different groups attached to it PLEASE WATCH LINK… https://www.bing.com/videos/search?q=diast ereomers+and+enantiomers&view=detail& mid=0C013CBDE313D6220C510C013CBDE3 13D6220C51&FORM=VIRE  Next Topic > Finish Carbohydrates