Chapter 17 Metabolism – An Overview Biochemistry by Reginald Garrett and Charles Grisham.
Biochemistry 2/e - Garrett & Grisham Copyright © 1999 by Harcourt Brace & Company Chapter 7...
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Transcript of Biochemistry 2/e - Garrett & Grisham Copyright © 1999 by Harcourt Brace & Company Chapter 7...
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Chapter 7
Carbohydratesto accompany
Biochemistry, 2/e
by
Reginald Garrett and Charles Grisham
All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Outline
• 7.1 Carbohydrate Nomenclature
• 7.2 Monosaccharides
• 7.3 Oligosaccharides
• 7.4 Polysaccharides
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Stereochemistry ReviewRead text on p. 210-213 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
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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 10.2 and 10.3 are diastereomers
• Two sugars that differ in configuration at only one chiral center are epimers
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Cyclic monsaccharide structures and anomeric forms
• Glucose (an aldose) can cyclize to form a cyclic hemiacetal
• Fructose (a ketose) can cyclize to form a cyclic hemiketal
• Cyclic form of glucose is a pyranose
• Cyclic form of fructose is a furanose
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Cyclic monsaccharide structures and anomeric forms
• Cyclic forms possess anomeric carbons
• For D-sugars, alpha has OH down, beta up
• For L-sugars, the reverse is true
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
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. 7.19 and Figure 7.20
• Note carefully the nomenclature of links! Be able to recognize alpha(1,4), beta(1,4), etc
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
7.4 PolysaccharidesFunctions: storage, structure, recognition
• Nomenclature: homopolysaccharide vs. heteropolysaccharide
• Starch and glycogen are storage molecules
• Chitin and cellulose are structural molecules
• Cell surface polysaccharides are recognition molecules
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Starch A plant storage polysaccharide
• Two forms: amylose and amylopectin
• Most starch is 10-30% amylose and 70-90% amylopectin
• Branches in amylopectin every 12-30 residues
• Amylose has alpha(1,4) links, one reducing end
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Starch A plant storage polysaccharide
• Amylose is poorly soluble in water, but forms micellar suspensions
• In these suspensions, amylose is helical– iodine fits into the helices to produce a blue
color
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Why branching in Starch?Consider the phosphorylase reaction...
• Phosphorylase releases glucose-1-P products from the amylose or amylopectin chains
• The more branches, the more sites for phosphorylase attack
• Branches provide a mechanism for quickly releasing (or storing) glucose units for (or from) metabolism
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
GlycogenThe glucose storage device in animals
• Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass
• Glycogen is stored energy for the organism
• Only difference from starch: number of branches
• Alpha(1,6) branches every 8-12 residues
• Like amylopectin, glycogen gives a red-violet color with iodine
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Dextrans A small but significant difference from
starch and glycogen • If you change the main linkages
between glucose from alpha(1,4) to alpha(1,6), you get a new family of polysaccharides - dextrans
• Branches can be (1,2), (1,3), or (1,4)
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Dextrans A small but significant difference from
starch and glycogen • Dextrans formed by bacteria are
components of dental plaque
• Cross-linked dextrans are used as "Sephadex" gels in column chromatography
• These gels are up to 98% water!
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Structural Polysaccharides Composition similar to storage
polysaccharides, but small structural
differences greatly influence properties • Cellulose is the most abundant natural
polymer on earth • Cellulose is the principal strength and
support of trees and plants
• Cellulose can also be soft and fuzzy - in cotton
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Structural Polysaccharides Composition similar to storage
polysaccharides, but small structural
differences greatly influence properties • Beta(1,4) linkages make all the
difference!
• Strands of cellulose form extended ribbons
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Other Structural Polysaccharides
Further reading - pages 232-235
• Chitin - exoskeletons of crustaceans, insects and spiders, and cell walls of fungi – similar to cellulose, but C-2s are N-acetyl
– cellulose strands are parallel, chitins can be parallell or antiparallel
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Other Structural Polysaccharides
• Alginates - Ca-binding polymers in algae
• Agarose and agaropectin - galactose polymers
• Glycosaminoglycans - repeating disaccharides with amino sugars and negative charges
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company
Biochemistry 2/e - Garrett & Grisham
Copyright © 1999 by Harcourt Brace & Company