chapter 7a' carbohydrates b and w

Principles of Biochemistry 1/e - Garrett & Grisham

Copyright © by Thomson-Learning, Inc

Chapter 7(Part 1 of 2)

Carbohydrates and Cell Surfaces

to accompanyPrinciples of Biochemistry With a

Human Focus, 1/eby

Reginald Garrett and Charles Grisham



Outline

• 7.1 Carbohydrate Nomenclature • 7.2 Monosaccharides• 7.3 Oligosaccharides • 7.4 Polysaccharides• 7.5 Glycoproteins• 7.6 Proteoglycans



7.1 Nomenclature

Carbohydrates are hydrates of carbon• Monosaccharides (simple sugars)

cannot be broken down into simpler sugars under mild conditions

• Oligo = "a few" - usually 2 to 10 • Polysaccharides are polymers of the

simple sugars



7.2 MonsaccharidesAn organic chemistry review

• Aldoses and ketoses contain aldehyde and ketone functions, respectively

• Triose, tetrose, etc. denotes number of carbons

• Aldoses with 3C or more and ketoses with 4C or more are chiral

• Review Fischer projections and D,L system



Stereochemistry ReviewRead text on p. 204-210 carefully!

• D,L designation refers to the configuration of the highest-numbered asymmetric center

• D,L only refers the stereocenter of interest back to D- and L-glyceraldehyde!

• D,L do not specify the sign of rotation of plane-polarized light!

• All structures in Figures 7.2 and 7.3 are D

• D-sugars predominate in nature



More StereochemistryKnow these definitions

• Stereoisomers that are mirror images of each other are enantiomers

• Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images are diastereomers

• Any 2 sugars in a row in 7.2 and 7.3 are diastereomers

• Two sugars that differ in configuration at only one chiral center are epimers



Cyclic monsaccharidestructures and anomeric forms

• Glucose (an aldose) can cyclize to form a cyclic hemiacetal.

• Fructose (a ketose) can cyclize to form a cyclic hemiketal

• Aldohexoses prefer the pyranose form • Ketohexoses prefer the furanose form



Fig. 7.5 The linear form of glucose cyclizes to the alpha (OH anti to C6) or beta (OH syn to C6) hemiacetal pyranose form. Glucose is an aldohexose. Carbon 1 is the anomeric carbon. The interconversion of the cyclic forms (?or ?anomers) is called mutarotation. The beta/alpha ratio for glucose is 63/37.



Fig. 7.6 The linear form of fructose cyclizes to the alpha (C2-OH anti to C6) or beta (C2-OH syn to C6) hemiketalfuranose form. Fructose is an ketohexose. Carbon 2 is the anomeric carbon.



Cyclic monsaccharidestructures and anomeric forms

• Cyclic forms possess anomeric carbons • For D-sugars, alpha (OH anti to 6C) has

OH down, beta (OH syn to 6C) up • For L-sugars, the reverse is true



Fig. 7.7 Glucose, an aldohexose, prefers the pyranose form



Fig. 7.8 Ribose, an aldopentose, prefers the furanose form



Fig. 7.9. All of glucose’s OH s can be placed equatorially, which makes glucose the most stable and most abundant of monosaccharides



Monosaccharide Derivatives• Reducing sugars: sugars with free

anomeric carbons - they will reduce oxidizing agents, such as peroxide, ferricyanide and some metals (Cu and Ag)

• These redox reactions convert the sugar to a sugar acid

• Glucose is a reducing sugar - so these reactions are the basis for diagnostic tests for blood sugar



Fig. 7.10 Oxidation of monosaccharides

C-1 = -ONIC

C-6 = -ORONIC

Both = -ARIC



GLUCOSE

GLUCOSEGLUCOSE

GALACTOSE ALLOSE MANNOSE

GALLOMAN



More Monosaccharide Derivatives

• Sugar alcohols: mild reduction of sugars • Deoxy sugars: constituents of DNA, etc. • Sugar esters: phosphate esters like ATP

are important • Amino sugars contain an amino group in

place of a hydroxyl group • Acetals, ketals and glycosides: basis for

oligo- and poly-saccharides



Fig. 7.12 some deoxy-monosaccharides and Ouabain, a poisonous glyco-steroid, or Cardiac glycoside that affects the heart rhythm.



Fig. 7.13 sugar phosphate esters metabolically important. The first two areGlycolysis intermediates; the third is ATP



Fig. 7.14 Substitution of an OH for an amine group, NH2, gives sugar amines.These are the basic blocks for glycosaminoglycans (heparin, chondroitin, etc)



Fig. 7.15 Muranic and neuroaminic acids are components of of the polysaccarides in higher order organisms as well as bacterial cell walls. The collective name of of the N-acetyl and N-glycolyl derivatives are sialic acids



Fig. 7.16 Further reaction of hemiacetals or hemiketals with another alcohol gives acetals and ketals, respectively.



Fig. 7.17 For example, reacting glucosewith a mole of methanol gives the ? and?methyl-glucosides. The anomeric carbondoes not mutarotate, and the new bond (CH3-O) is Called a GLYCOSIDIC BOND



7.3 OligosaccharidesDon't memorize structures, but know the

important features• Be able to identify anomeric carbons and

reducing and nonreducing ends • Sucrose is NOT a reducing sugar • Browse the structures in Fig. 7.18, 7.19• Note carefully the nomenclature of links! Be

able to recognize alpha(1,4), beta(1,4), etc



Oligosaccharides (cont.)

• Glycolipids and glycoproteins• Found in cell membranes or secreted

proteins. Their function might be:• Allow attachment & solubility of proteins• Help proper folding (steric crowding)• Charged sugar repel ea other and extent the

3rd structure.• Protection from degradation• Recognition (cell signalling)



Oligosaccarides (cont.)

• Glycophorin (GP) of RBC membranes has 16 oligosaccarides(60-70 monosaccarides)

• They are the MN (GP) blood types (other glycoproteins)

• Soluble glycoproteins include immunoglobulins and transport proteins.

• They usually end in sialic acid (SI). If SI lost, they are degraded by liver

• Mann-6-P is signal for lysoenzymes to move to lysosomes.



Fig. 7.18 examples of glycosidic bonds. The sugar using the anomeric carbon is named first. (Acrobat)



Fig. page 217. TREHALOSE , glucose-?-1,1-glucose, is a temperature protectant forinsects (they have hemolymph, not blood), fungi, yeast, bacterial spores, etc. Honey bees do not have it. They keep their honeycomb at 18 0C at all times.



Fig. 7.19 Other oligosaccharides. The cycloamylose is useful for size exclusion chromatography. Leatrile killed Steve Mcqueen.

chapter 7a' carbohydrates b and w

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