Chapter 11- Sugars and polysacharrides Flashcards
Oligosacharides
few covalently linked monosaccharide units.
glucoconjugates
glucoproteins and glucolipids collectively
simple sugars or monosacharides are what
ketone or aldehyde derivatives of straight-chain polyhydroxyl alcohols containing atleast 3 carbons
Can these simple sugars such as D-glucose or D-Ribulose be hydrolyzed to form simpler saccharides?
NO
A ketone
O
II
R - C - R’
An aldehyde
O
II
R - C - H
if the carbonyl group is an aldehyde then the sugar is an
aldose
If the carbonyl group is a ketone then the sugar is called a
ketose
A three carbon chain sugar is a
triose
A four carbon chain sugar is a
tetrose
A five carbon chain sugar is a
pentose
A six carbon chain sugar is called a
hexoses
A seven carbon chain sugar is a
heptose
A glucose is also called _____ because glucose has a _____ derivative with _____ carbon chain
glucose is a aldohexoses since glucose is an aldehyde derivative with a six carbon chain
A Ribulose is also called ______ because Ribulose has a ______ derivative with _____ carbon chain
Ribulose is called a ketopentose since it has a ketose derivative with a five carbon chain.
Monosacharides are classified according to ________
chemical nature of their carbonyl group and number of carbon atoms
All of D-glucose’s carbons but _____ of six are chiral centers and these are carbon ____ and ____.
All but two of six of D-Glucose’s carbons are chiral centers and these are carbon 1 and carbon 6.
How can you determine the number of stereoisomers of aldoses?
n-carbon aldoses have 2^(n-2) stereoisomers
How many stereoisomers does Glucose have ?
2^(6-2) = 2^4 = 16 stereoisomers
Sugars that differ by the configuration of 1 carbon are called
epimers of one another.
Are D-glucose and D mannose epimers of each other?
Yes in respect to carbon 2
Are D-glucose and D-galactose epimers of eachother?
yes by respect to carbon 4
Are D mannose and D galactose epimers of each other?
NO because they have two different carbons configurations not one.
What is the only aldose that commonly occurs in nature as a monosacharide?
D-glucose
____ sugars are significantly less abundant than _____ sugars
L sugars are significantly less abundant than D sugars
How many achiral centers does ketoses have?
3
What is the general equation in determining the number of stereiosmers of a ketose?
2^(n-3)
The most common form of ketose is when the ketone is at carbon _____
2
Alcohols react with the carbonyl groups of aldehydes to form
hemiacetals
Alcohols react with the carbonyl group of ketones to form
hemiketals
The hydroxyl in either the aldehyde or ketone can react intramolecularly to form ____ and ____
cylic hemiacetals and cylic hemiketals.
The configuration of cylic hemiacetals and cylic hemiketals are represented how?
Haworth projection formulas
A sugar with a six membered ring is known as ___
pyranose
A sugar with a five membered ring is known as ___
furanose
The cylic form of glucose is called ____
glucopyranose
The cylic form of fructose is called ____
fructofuranose
The cyclization of a monosaccharide renders the former carbonyl carbon asymmetric. The resulting pair of diasteromers are known as ____ and the hemiacetal or hemiketal carbon is referred to as the _____ carbon
anomers and the heiacetal or hemiketal carbon is referred to as the anomeric carbon
In the alpha anomer the OH substituent to the anomeric carbon is ____ of the sugar ring from the CH2OH group at the chiral center that designates the D or L configuration.
on the opposite side
In the beta anomer the OH substituent to the anomeric carbon is _____ of the sugar ring from the CH2OH group at the chiral center designated D or L
is on the same side
How does the specific rotations of alpha glucose and beta glucose differ?
alpha is +112.2 and Beta is +18.7
What happens to specific rotation when a pure alpha or pure glucose substance is dissolved in water? what is this phenomena called?
The optical rotation changes slowly until it reaches an equilibrium value of _52.5 degrees. This is called mutarotation.
The mutarotation in glucose results in what?
an equilibrium optical rotation of _52.7 degrees and an equilibrium mizture containing 63.6% of thee Beta anomer and 36.4% of the alpha anomer.
The optical rotations of separate molecules in solution are ____ of each other so the optical rotation of a solution is ____
The optical rotations of separate molecules in solution are independent of each other so the optical rotation of a solution is the weighted average of the optical rotations of its components.
Do Hexoses assume pyranose of furanose form?
They can assume Both
Do pentoses assume pyranose or furanose form?
They can assume both
What form does glucose assume in aqueous solutions?
almost entirely pyranose form
What form does fructose assume in aqueous solutions?
67% pyranose form and 33% furanose form.
What form does ribose assume in aqueous solutions?
75% pyranose and 25% furanose.
What form does gucose assume in polysacharides?
almost entirely pyranose
What form does fructose assume in polysacharides?
almost entirely furanose
What form does ribose assume in polysacharides
almost entirely furanose
Rings of seven or more can form so why are they rarely observed?
because the greater stabilities of the five- and six- membered rings of these sugars can also form.
What makes 3 and 4 membered sugar rings unstable with respect to linear forms?
Internal strain
Why can’t furanose and pyranose rings be planar
all atoms in ring are tetrahedrally (sp^3) hybridized.
In the chair conformation the equatorial position is ____ and the axial position is ___
equaitorial position is outward
axial position is verical
In deciding what chair formation is correct sterics plays a role how?
The least sterically hindered predominate thus typically where the bulky substituents occupy equitorial positions
What is the only D-aldohexose in which all non H substituents occupy the equitorial postion
Beta-D- Glucopyranose
In acid catalyzed reactions the anomeric hydroxyl of a sugar reversibly condenses with alcohol to form ____
alpha and Beta glycosides.
the bond connecting the anomeric carbon to the acetal oxygen is ____
a glycosidic bond.
How are polysacharides held together?
glycosidic bonds
The hydrolysis of glycosidic bonds is catalyzed by
enzymes known as glycosidases
Glycosidases differ in specificity to _____ but are rather insensitive to ____
Differ in specificity to the identity and anomeric configuration of the glycoside but are rather insensitive to the identity of the alcohol residue.
Do glycosides undergo mutarotation like monosacharides? Why or why not?
No because because under basic or neutral conditions in the absence of glycosidases the glycosidic bond is stable.
Mild oxidation of an aldose results in conversion of aldehyde group to a _______ yielding ___
conversion of aldehyde to carboxylic acid function yielding aldonic acid
How are aldonic acids named?
By adding -onic to the root name of its parent aldose such as gluconic acid.
What are reducing sugars?
Saccharides bearing anomeric carbon atoms that have not formed glycosides. They facility with which the aldehyde group reduces mild oxidizing agents.
What is a classic test that test for the presence of a reducing sugar is ___
the reduction of Ag+ in an ammonia solution (Tollen’s reagent) to yield a metallic silver mirror lining on the inside of the reaction vessel.
The specific oxidation of the primary alcohol group of aldoses yields _____ which are named how?
uronic acid which are named by appending -uronic acid to the root name of the parent aldose such as D-Glucuronic acid, D-galacturonic acid and D-mannuronic acid.
Both aldonic and uronic acids have a strong tendency to internally ____ so as to form _____
to internally esterify so as to form f or 6 membered lactones
Ascorbic acid (vitamin C) is a ___ lactone that is synthesized by ____
Y lactone synthesized by plants and almost all animals except primates and guinea pigs.
What happens in the prolonged deficiency of ascorbic acid in the diet of humans?
Scurvy which causes an impairment of collagen formation which generally results in a lack of fresh food.
Why is ascorbic acid related to scurvy?
Under physiological conditions, ascorbic acid is reversibly oxidized to dehydroascorbic acid which is irreversibly hydrolyzed to the vitamin-inactive diketogulonic acid.
Aldoses and ketoses may be reudced under mild conditions by treatment of NaBH4 to yield _____
acyclic polyhydroxyl alcholds called alditols
How are alditols named
by adding the suffix -itol to the root name of the parent aldose.
the polyhydroxy alcohol myo-inositol is a what component?
a lipid component
Xylitol is what?
a polyhydroxy alcohol; it is also a sweetener used in sugarless gum and candy.
What are deoxy sugars?
sugars in which an OH group is replaced by H
In amino sugars one or more ____ groups are replaced by _____
one or more OH groups are replaced by an often acetylated amino group.
The amino sugar derivative N-acetylmuramic acid consists of ____ in an ether linkage to ____
consists of a N-acetyl-D-glucosamine in an ether linkage with D-lactic acid.
N-acetylmuramic acid is a prominent component of ____
bacteria cell walls.
N-acetylneuraminic acid is dervied from ____ and ____
N-acetylmannosaminic acid and pyruvic acid
N-acetylneuraminic acid is an important constituent of ____ and ___
glycoproteins and glycolipids
N-acetylneuraminic acid and its derivatives are reffered to as ___
sialic acids.
Polysaccharides are also known as what?
glycans
A homopolyscharide consists of _____ monosacharide reidues
one type of
A heteropolysacharide consists of _____ monosacharide residues
more than one type
homopolysacharides can be further classified how?
According to idenity of monomeric units
What are glucans?
polymers of glucose