Ch 4 - Carbohydrates

Question 1

monosaccharides

Answer 1

• triose - simplest, 3C
• tetrose, pentose, hexose
• aldose - aldehyde as most oxidized group
• ketose - ketone as most oxidized group
• glycosydic linkages - connecting sugars
  
  • glycosyl residues
• every carbon except carbonyl will have hydroxyl group

Question 2

Common sugars

Answer 2

• know these structures
• fructose
• glucose
• galactose
• mannose
• glyceraldehyde
• sucrose
• lactose
• maltose

Question 3

stereoisomers

Answer 3

• same chemical formula, different spacial arrangement
• number of steroisomers = 2ⁿ
  
  • n = number of chiral carbons
• enantiomers - nonidentical, nonsuperimposable mirror images
  
  • absolute configuration - 3D arrangement of chiral carbons
    
    • D and L, (based on Fischer projection)where D has hydroxide on the right of the highest numbered chiral carbon
    • L has hydroxide on the left of the highest numbered chiral carbon
• diastereomers - same formula, same family (ketose/aldose), not identical, not mirror images
• (+) and (-) rotation determined experimentally
• Epimers - type of diastereomer, differ in configuration at exactly one carbon

Question 4

Fischer Projection

Answer 4

• horizontal lines - wedge bond (out of page)
• vertical lines - dash bond (into page)
• Haworth projection - planar cyclic diagram
  
  • right on Fischer is down on Haworth
  • “Down right up li(e)fting

Question 5

hemiacetals/hemiketals

Answer 5

• pyranose - 6 member ring
• furanose - 5 member ring
• hemiacetal - form from intramolecular reaction of aldose
• hemiketal - form from intramolecular reaction of ketose
• hydroxyl group acts as nucleophile and that oxygen becomes a member of the ring
• anomeric carbon - carbonyl carbon that becomes chiral in the process of ring formation
  
  • anomers - 2 possibilities formed due to chiral carbon
  • alpha-anomer is C-1 hydroxide is trans to CH2OH
  • beta-anomer is C-1 hydroxide is cis to CH2OH
• Mutarotation - switching between alpha and beta configurations
  
  • can be acid or base catalyzed. occurs in water
  • beta favored in water

Question 6

Reducing Sugars

Answer 6

• aldose oxidized to a aldonic acid (carboxylic acid)
• monosaccharides with hemiacetal rings are reducing sugars
• when aldose in ring, then form a lactone, cyclic ester with carbonyl carbon as the former anomeric carbon
• testing for reducing sugars:
  
  • Tollen’s Reagent is [Ag(NH3)2]+ reduced to make silvery mirror if aldehyde is present
  • Benedicts reagent - aldehyde group oxidized and Cu2O red precipitate
  • glucose oxidase to test specifically for glucose
• ketose as a reducing sugar
  
  • positive Tollen and Benedicts test
  • cannot be oxidized directly
  • tautomerization - rearrangement of bonds in a compound
    
    • keto-enol shift
    • from enol to aldehyde and then reduced
• alditol - aldehyde of an aldose is reduced to alcohol
• deoxy sugar - hydrogen replaces hydroxyl group on sugar
  
  • D-2-deoxyribose (from DNA)

Question 7

Esterification of Carbohydrates

Answer 7

• Carboxylic acid derivative reacts with primary alcohol on carbohydrate to form ester
• similar to phosphylation of glucose in glycolysis

Question 8

Glycoside Formation

Answer 8

• acetal - hemiacetal react with alcohol
  
  • called glycosides
• occurs on anomeric hydroxyl group
  
  • forms alkoxy group
• C-O bonds are glycosidic
• disaccharides/polysaccharides are from glycosydic bonds between monosaccharides
• furanosides and pyranosides
• breaking the bond requires hydrolysis

Question 9

Disaccharides

Answer 9

• anomeric carbon of one monosaccharide can react with any hydroxyl group on the other
• example: alpha-1,6 alpha anomeric carbon (C-1) of the first glucose attached to the C-6 of the other glucose
• bond of 2 anomeric carbons. alpha, alpha-1,1
• KNOW sucrose, lactose, maltose
• sucrose (glucose-a-1, 2-fructose) - nonreducing sugar
• lactose (galactose-B-1, 4-glucose)
• maltose (glucose-a-1, 4-glucose)

Question 10

Polysaccharides

Answer 10

• homopolysaccharide - made of the same monosaccharides
  
  • heteropolysaccharide - different monosaccharides
• Cellulose -
  
  • B-D-glucose linked by B-1, 4 glycosidic bonds, linear
    
    • not digested by humans, aka fiber
• Starch -
  
  • a-D-glucose
  • amylose - how plants store starch
    
    • a-1,4 glycosidic bonds, linear
  • amylopectin - amylose with a-1,6 branches
  • alpha-amylose cleaves randomly to yield shorter chains of maltose and glucose
  • beta-amylose cleaves amylose at nonreducing ends, yields maltose
• Glycogen - storage unit in animals
  
  • more branched than starch
  • more a-1,6 so highly branched
  • makes more soluble and efficient
  • a 1,4 bonds too
  • a-D-glucose monomer
  • glycogen phosphorylase cleave glucose from nonreducing end and phosphorylate it
    
    • can work on many branches at once