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The simplest aldose sugar, __ has __ chiral center(s)
glyceraldehyde (3 C’s); 1
(See slide #2)
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The simplest ketose sugar, __ has __ chiral center(s)
Dihydroxyacetone (3 C’s); 0 (achiral)
(See slide #2)
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A reaction between __ results in a hemiacetal
an aldehyde (C1) & an alcohol (C5)
(during the cyclization of an aldohexose such as glucose. See slide #3)
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Glucose has ___ stereoisomers in Fischer form & __ stereoisomers in Haworth form
- 2^4 = 16 stereoisomers;
- 2^5 = 32 stereoisomers
(See slide #2 & 3)
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In alpha, the anomeric OH is __ to CH2OH in a pyranose. In beta, the anomeric OH is __
trans (or axial when in chair conformation); cis (or equatorial when in chair conformation)
(See slide #3)
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Epimers & their OH positioning
Epimers differ at the positioning of the OH group at one chiral carbon. Remember 2-3-4-MAG
- Mannose (epimer @ C2)
- Allose (epimer @ C3)
- Galactose (epimer @ C4)
(See slide #4)
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A reaction between __ results in a hemiketal
a ketone (C2) & an alcohol (C5)
(during the cyclization of a ketohexose such as fructose. See slide #6)
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In both D-glucopyranose & D-fructofuranose, which is more stable? In alpha or beta form?
beta (less steric clash)
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Fructose has __ stereoisomers in Fischer form & __ stereoisomers in Haworth form
- 2^3 = 8 stereoisomers;
- 2^4 = 16 stereoisomers
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reducing sugars
- has a free OH in its anomeric carbon
- can mutarotate
- will produce a positive Benedict’s or Tollens test
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In the Tollens & Benedict’s reagent test, what is being oxidized & what is reduced?
The sugars are oxidized & the metals are reduced
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What does a positive & negative Benedict’s test look like?
- Negative: blue
- Positive: copper color precipitate (since copper is the metal used)
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What does a positive & negative Tollens test look like?
- Negative: clear
- Positive: silver precipitate (since silver is the metal used)
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non-reducing sugars
- glycosides
- CANNOT mutarotate
- will produce a negative Benedict’s or Tollens test
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What does a Maltose structure look like? (Need to know how to draw)
2 Glucoses with a 1-4 glycosidic linkage
(See slide #8)
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How many stereoisomers does a disaccharide have (in Haworth form)?
2^(10 chiral centers) = 1024 stereocenters
5 chiral centers for each sugar. See slide #8
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What does a Lactose structure look like? (Need to know how to draw)
a Galactose + a Glucose with a 1-4 glycosidic linkage
(See slide #8)
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concept of a sugar glycoside
- when an anomeric carbon of one sugar reacts with the anomeric carbon of another sugar (hence no free anomeric OH groups)
- when an anomeric OH is transformed into an OR
(See Ex. 2 on slide #11)
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Branched carbohydrate polymer found in animals
Glycogen
Note: All other carbohydrate polymers are found in plants. The one whose structure is exactly like Glycogen is Amylopectin. The other 2 are not branched.
(See table on slide #12)
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Branched carbohydrate polymer found in plants
Amylopectin
Note: Amylopectin’s structure is exactly the SAME as Glycogen.
(See table on slide #12)
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Non-branched carbohydrate polymer that has alpha1-4 as the main chain
Amylose
(Also has a helical shape but won’t show that in a 2D structure)
(See table on slide #12)
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Non-branched carbohydrate polymer that has beta1-4 as the main chain
Cellulose
Note: All other carbohydrate polymers have alpha1-4 as the main chain
(See table on slide #12)
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Functions of carbohydrate polymers
- Glycogen, Amylopectin, & Amylose: energy storage
- Cellulose: structural support
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glycosidic linkage of the branch of carbohydrate polymers
alpha1-6
(Occurs in branches of Glycogen & Amylopectin. See slide #13)
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