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BIOC- Carbs

Carbohydrates

QuestionAnswer
Simplest sugar molecules monosaccharides (one sugar)
Chemical properties that all monosaccharides share very water soluble, poorly soluble in organic solvents, colorless, and most are sweet
Monosaccharides contain two organic functional groups? carbonyl (C=O) group (ketone or aldehyde)and at least 2 carbons bearing hydroxyl groups Therefore sugars are polyhydroxy aldehydes (aldose) or polyhydroxy ketones (ketose)
Simplest sugars? Triose (contain 3 carbon atoms -one carbonyl group and 2 carbons with hydroxy groups)
What are the two trioses? Aldose (glyceraldehyde) and ketose (dihydroxyacetone)
Why are glycerol and acetone not sugars? p.257 Sugars contain one carbonyl group and 2 carbons with hydroxy groups
Chiral Four substituents on carbon are all different allowing it to exist in either a right handed or left handed form.
Have identical chemical properties with assymetrical structure - left hand and right hand form of mlc.When polarized light is passed through mlcs the plane of polarization is bent in opposite directions for each. (handedness=optical activity) enantiomer (left hand+ left foot = right hand + right foot)
single molecule has more than one chiral carbon atom that differs in handedness at one carbon but not at the other - do NOT have identical chemical properties (spatial relationship among atoms are different) diastereomer (left hand + right foot = right hand + left foot) see p.261 example
What is the simplest aldose sugar? glyceraldehyde
How do you know if the sugar is in D configuration? the C carbon farthest (really the second last carbon) from the carbonyl group has the OH group to the right
Who is famous for the study of sugars and carboyhdrate chemistry? He established the stereochemical configuration of all the known sugars and isomers. He also synthesized glucose fructose and mannose from glycerol. Emil Fischer
Every carbon atom in a simple sugar bears a single OH group except the carbonyl carbon
Looking at the D form of a sugar you should be able to write the L form only the second carbon from the end farthest from the carbonyl group is changed. In D form the OH is on the right.
Every time another C atom is added to a sugar carbon chain what happens to the number of isomers? doubles
A pair of sugar isomers that are identical except for chirality at one carbon atom epimers (a special case of diasteromers)
For a carbon chain of a given number what is the relationship between the number of ketoses and aldoses? There are always twice as many aldoses compared to ketoses for a given number of carbons
What is a common property of all sugars?a) taste sweet b)contain OH group c)contain aldehyde group d)have at least 4 C atomse) are reducing agents They all contain an OH group
What affect does CU2+ ion have on sugars? Some oxidants such as the cupric ion can oxidize the aldehyde groups of aldose sugars to the corresponding acids. The cupric ion (CU2+) gets reduced to the cuprous ion (CU+) which forms a red precipitate. =reducing sugar
What type of sugar is sucrose (table sugar)? non-reducing
Who detected the presence of sugar and measured blood glucose when isolating insulin in the 1920s? Dr. Banting
What type of sugar is fructose? reducing ketose (ketoses can also be reducing but react more slowly than aldoses)-under basic conditions ketoses slowly isomerize into aldoses)
Aldehyde + alcohol = hemiacetal (see p.268)
ketone + alcohol = hemiketal (see p.268)
sugars have both alcohol and aldehyde or ketone functional groups, therefore reaction is _______________ intramolecular (alcohol and aldehyde are present in same molecule) therefore reaction is quick and easy. see p. 269
since there are 5 different OH groups in glucose which one reacts with aldehyde any one can react but the OH group at C-5 is the one in the best position to reach and the result = nice stable 6 member ring (p.269)
What are anomers? Epimers resulting from the cyclization of a sugar. They are distinguished as alpha (OH is same side) or beta (OH opposite side)(see p.269)
The carbon bearing the the anomeric OH group is called what? anomeric carbon (this is C1 for an aldose sugar)
In a 6-C ring which carbon is responsible for contributing the OH to form a hemiacetal? C5
The interconversion of alpha and beta forms of a sugar (which occurs slowly in a solution) and leads to an equilibrium mixture of the two forms is known as? Mutarotation (when glucose is in solution the degree of rotation of the plane of polarized light would gradually change)
Both the ring and linear forms of glucose exist. Which one is an aldehyde? the linear form is an aldehyde but the ring isnt
If the OH group points to the left in the fischer formula it goes where in the ring? It goes above the ring in the Haworth formula (OH to the right goes below) *note rule is opposite for L sugars
If the anomeric OH group is above the ring what form is it in? beta (left above beta)
How do you recognize which carbon is the anomeric carbon in the haworth projection? It is the only carbon atom in the molecule that is linked to two different oxygen atoms
What is the name for a five membered ring and a six membered ring? 5=furanose 6=pyranose
What can form pyranose rings? aldoses or ketoses having 5 or more C atoms
Why do we get different sizes of rings? (pyranose vs. furanose) it depends on the relative stabilities of the possible cyclic products and this depends on the geometry of the molecule.
All the aldo-hexoses form predominantly ______rings pyranose (ie. glucose has a strong tendency to form pyranose)
Ribose is an aldo pentose which forms a ______ ring furanose ring because it is too small to form a stable pyranose ring
Why is the anomeric carbon atom of a sugar so reactive? It is the only carbon atom bonded to two O's. H+ is added to the anomeric carbon, H2O is released resulting in a resonance stabilized structure with a free proton therefore making anomeric carbon reactive (can react with alcohol)p.277
Explain the cyclization of a ketose electrophilic carbonyl carbon atom reacts with the nucleophilic O of an OH group and a carbon atom is in the anomeric carbon position p.270
If a sugar react with alcohol in a condensation reaction what is the product? glycosides are products of condensation of alcohols with the anomeric OH group of a sugar
_______can react at the anomeric carbon nucleophiles (have lone pairs of electrons)rxn is condensation and new bonds are formed
When nucleophiles react with anomeric carbon a bond is formed. What are the bonds formed when an alcohol or amine react? alcohol= C-O (glycosidic bond)amine= C-N (glycosylic bond)
What is the most important rxn for sugars? glycoside formation
Sugars are also alcohols so any OH group on a sugar can act as a _______and form a glycosidic bond to the anomeric carbon of another sugar (how sugar polymers are formed) nucleophile
What happens if the anomeric OH group of a sugar is no longer free? then the sugar cannot be easily oxidized (it is non-reducing)*we would need to break the O-H bond of the anomeric group but we cant in glycoside b/c that H atom is gone therefore cant open up to linear form and therefore not reducing
How is a disaccharide built? from 2 simple sugars by condensation (glycosidic bond) the anomeric C of one sugar is the electrophile and any one of the OH groups of the second sugar is the nucleophile
What is lactose formed by? gal(Beta1 -> 4)glc or carbon 1 of the beta galactose with carbon 4 of the alpha glucose Note that glucose and galactose can also form many isomers of lactose
The orientation of the OH group on the anomeric carbon when forming a dissacharide must be which way? It can be either up or down (beta or alpha)
The formation of a glycosidic bond of a dissacharide must involve what? the anomeric C of one sugar (electrophile)and an OH group of the second sugar (anomeric or not)Thus resulting in several possible isomers
Is lactose a reducing sugar? Yes anomeric C of glucose is still free
If the anomeric OH group is still free it can ___ open up into the open chain aldehyde form therefore making it a reducing sugar (also reducing sugars can undergo mutarotation and exist in either alpha or beta form
How can a dissacharide be a non reducing sugar If a glycosidic bond is formed between the anomeric C of one sugar and the anomeric OH group of the other
How can a dissacharide be a reducing sugar if the anomeric OH group is still free in one of the sugars (any reducing sugar can undergo mutarotation)
polysaccharides can have thousands of sugar subunits. If they are all the same subunits it is referred to as ... homopolysaccharide (polysaccharides are often highly branched)
If polysaccharides are built from two or more kinds of subunits they are referred to as.. heteropolysaccharide
How can branching happen in polysaccharides? sugars have several OH each of which can act as the nucleophile in forming a glycosidic bond.
gluconeogenesis is what type of metabolic pathway? ANABOLIC - generates glucose from non carb carbon substrates
glycogenesis is what type of metabolic pathway? Anabolic - generates glycogen from glucose molecules
glycolysis is what type of metabolic pathway? catabolism - converts glucose to pyruvate
citric acid cycle is what type of metabolic pathway catabolism - converts CHO, fat, protein into CO2 and water
Created by: MichBo on 2010-01-08



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