Carbohydrates Flashcards
Reactions of carbohydrates
Monosaccharide
Single carbohydrate unit. Example: glucose
Reactions of carbohydrates
Bonding
Monosaccharide units can form into disaccharides or polysaccharides linked by glycosidic bonds.
Glycosidic bonds form from nucleophilic attack onto the anomeric carbon of a sugar.
These bonds can be α or β. To determine this, look at whether the -OH group of the anomeric carbon is pointing up (β) or down (α).
Reactions of carbohydrates
Esterification
Alcohols plus carboxylic acids (and derivatives) result in esters.
Reactions of carbohydrates
Phosphorylation
Phosphorylation of a sugar by ATP results in a phosphate ester.
Reactions of carbohydrates
Reducing sugars
Sugars with a ketone or aldehyde group containing a free anomeric carbon that can be oxidized are capable of serving as reducing agents.
In cyclic form, reducing sugars have hemiacetal or hemiketal configurations.
Reactions of carbohydrates
Reducing saccharides
Remember that a sugar must have a free anomeric carbon to act as a reducing sugar.
All free monosaccharides are reducing, whereas disaccharides are reducing if they have a free anomeric carbon not participating in a glycosidic bond.
For example, sucrose has a glycosidic bond between anomeric carbons and therefore is nonreducing.
Key monosaccharides
Glucose
Most common monosaccharide
Key monosaccharides
Galactose
A monosaccharide that is an epimer of glucose at C4.
Comes from milk and is converted to glucose in the liver.
Key monosaccharides
Fructose
A monosaccharide found in foods like honey. Converted to glucose in the liver.
Be able to recognize glucose, galactose, and fructose.
Key disaccharides and polysaccharides
Maltose
Disaccharide made of glucose and glucose linked by a α-1,4-glycosidic bond.
Key disaccharides and polysaccharides
Lactose
Disaccharide made of galactose and glucose linked by a β-glycosidic bond.
Key disaccharides and polysaccharides
Sucrose
Disaccharide made of glucose and fructose linked by a α-1,2-glycosidic bond.
Key disaccharides and polysaccharides
Cellulose
A polysaccharide connected by β-glycosidic bonds, functions as the main component of plant cell walls.
Stereochemistry of carbohydrates
Stereochemistry
Carbohydrates are generally structures with enantiomers and can be in D- or L- configurations.
To find the configuration, look at the C furthest from the carbonyl group (highest chiral number). The -OH group on the left means L-configuration.
In nature, carbohydrates are found in the D-configuration.
Stereochemistry of carbohydrates
Epimers
Epimers are a subtype of diastereomers that differ at one and only one chiral carbon.
Stereochemistry of carbohydrates
Anomer configurations
Anomers are epimers formed by ring closure and can have α or β stereochemistry.
α-anomers have the -OH on the anomeric carbon trans to the CH2OH group. The -OH group will be pointing down.
β-anomers have the -OH on the anomeric carbon cis to CH2OH group. The -OH group will be pointing up.
