Lecture 12 Flashcards
(24 cards)
What is the anomeric carbon?
The anomeric carbon is the carbonyl carbon in the open-chain form of a sugar. In the ring form, it becomes a new chiral center.
How do α- and β-anomers of glucose differ?
In α-D-glucopyranose, the hydroxyl (-OH) group on the anomeric carbon is opposite the CH₂OH group.
In β-D-glucopyranose, the hydroxyl (-OH) group on the anomeric carbon is on the same side as the CH₂OH group.
What are the two common cyclic forms of monosaccharides?
Furanoses (5-membered rings)
Pyranoses (6-membered rings)
What are phosphate esters, and why are they important?
Phosphate esters form when a phosphate group attaches to a sugar’s hydroxyl group.
Example: Glucose-1-phosphate, a key molecule in metabolism.
What are sugar acids and lactones?
Sugar acids form by oxidation of an aldose. Example: Gluconic acid.
Lactones are cyclic esters formed from sugar acids.
What is a reducing sugar?
A sugar with a free anomeric carbon that can reduce Cu²⁺ or Ag⁺ ions.
Example: Glucose is a reducing sugar.
What is Fehling’s test?
A chemical test that detects reducing sugars by producing a red Cu₂O precipitate.
What are alditols (sugar alcohols)?
Reduced forms of monosaccharides where the aldehyde/ketone is converted into an alcohol.
Example: Sorbitol (Glucitol).
What is the role of sorbitol in metabolism?
Sorbitol is an intermediate in glucose-to-fructose conversion via aldose reductase and sorbitol dehydrogenase.
What are amino sugars?
Monosaccharides where an amino group (-NH₂) replaces a hydroxyl (-OH).
Example: Glucosamine, important for glycoproteins and bacterial cell walls.
What are glycosides?
Sugars where the anomeric carbon forms an acetal or ketal bond with another molecule.
How do glycosides differ from hemiacetals/hemiketals?
Glycosides are stable and do not interconvert between α- and β-forms.
What is a glycosidic bond?
A bond between the anomeric carbon of one sugar and the hydroxyl group of another.
What are disaccharides?
Carbohydrates formed by linking two monosaccharides via a glycosidic bond.
Example: Maltose (Glucose-α(1→4)-Glucose).
What makes a disaccharide reducing or non-reducing?
Reducing disaccharides have a free hemiacetal at the anomeric carbon.
Non-reducing disaccharides have both anomeric carbons locked in glycosidic bonds.
What are polysaccharides?
Long chains of monosaccharides linked by glycosidic bonds.
What are the two main types of polysaccharides?
Storage polysaccharides (starch, glycogen).
Structural polysaccharides (cellulose, chitin).
What is starch composed of?
Amylose (linear, α(1→4) glucose polymer).
Amylopectin (branched, α(1→4) with α(1→6) branches every 12-30 residues).
How does glycogen differ from starch?
Glycogen is like amylopectin but more highly branched, with α(1→6) branches every 8-12 residues.
What makes cellulose different from starch and glycogen?
Cellulose is a β(1→4) glucose polymer, forming strong fibers due to extensive hydrogen bonding.
Why can humans digest starch but not cellulose?
Humans have α-amylase, which breaks α(1→4) bonds in starch but lack cellulase to break β(1→4) bonds in cellulose.
What is chitin, and how is it related to cellulose?
Chitin is a β(1→4) polymer of N-acetylglucosamine, found in arthropod exoskeletons.
How does glycosidic bond stereochemistry affect polysaccharide properties?
α(1→4) bonds (starch & glycogen) create soluble, flexible structures.
β(1→4) bonds (cellulose & chitin) create rigid, insoluble fibers.
What are reducing and non-reducing ends in polysaccharides?
The reducing end has a free hemiacetal, while the non-reducing end is locked in a glycosidic bond.
