monosaccharides

A collection of question-and-answer flashcards covering the key concepts from the monosaccharide lecture notes, including classification, structure, ring forms, anomers, major reactions, and general carbohydrate biology.

What are monosaccharides and what are their characteristic properties?

Monosaccharides are the simplest carbohydrates and the basic building blocks of more complex sugars. They are colorless, crystalline solids, soluble in water, and have a sweet taste.

How are monosaccharides classified by the number of carbon atoms? List the four classes and one example for each.

Trioses (3 C): glyceraldehyde, dihydroxyacetone; Tetroses (4 C): erythrose; Pentoses (5 C): ribose, deoxyribose, xylose, arabinose; Hexoses (6 C): glucose, fructose, galactose, mannose.

What defines an aldose and what are examples?

Aldoses contain an aldehyde group (R-CHO) at one end of the carbon chain; examples include glucose, galactose, ribose.

What defines a ketose and where is the carbonyl group typically located?

Ketoses contain a ketone group (R-CO-R'), typically at the second carbon; examples include fructose and dihydroxyacetone.

What forms do monosaccharides exist in, and which form dominates in aqueous solutions?

Monosaccharides exist in open-chain and cyclic forms; cyclic forms are predominant in aqueous solutions.

What happens during cyclization of a monosaccharide?

The carbonyl group reacts with a hydroxyl group within the same molecule to form a ring, yielding a hemiacetal (aldose) or a hemiketal (ketose) and creating an anomeric carbon.

What is a pyranose ring and give an example?

A pyranose ring is a six-membered ring (5 carbons + 1 oxygen); example: α-D-glucopyranose.

What is a furanose ring and give an example?

A furanose ring is a five-membered ring (4 carbons + 1 oxygen); example: β-D-fructofuranose.

What are anomers in carbohydrates?

Anomers are stereoisomers that differ in the orientation of the hydroxyl group on the anomeric carbon after cyclization.

Define the a- and B-anomers in terms of the anomeric carbon and CH2OH group.

a-anomer: hydroxyl on the anomeric carbon is on the opposite side of the ring from the CH2OH group at the highest-numbered chiral carbon; B-anomer: hydroxyl on the anomeric carbon is on the same side as the CH2OH group.

What is mutarotation and what intermediate is involved?

Mutarotation is the interconversion between aldose and ketose forms (and epimers) occurring via an enediol intermediate.

What are aldonic acids and how are they formed? Give an example and a testing context.

Aldonic acids are formed by oxidation of the aldehyde group of aldoses (e.g., glucose to gluconic acid); this oxidation relates to Benedict's and Fehling's tests for reducing sugars.

What are uronic acids and how are they formed?

Uronic acids are formed by oxidation of the terminal primary alcohol group (C-6) of hexoses (e.g., glucose to glucuronic acid); important in detoxification and polysaccharide synthesis.

What are saccharic (aldaric) acids and how are they formed?

Saccharic acids are formed by oxidation of both the aldehyde and the terminal primary alcohol ends of aldoses (e.g., glucose to glucaric acid).

What are alditols (sugar alcohols) and how are they formed?

Alditols are formed by reduction of the carbonyl group of a monosaccharide to a hydroxyl group; examples include glucose to sorbitol; fructose to sorbitol and mannitol; xylose to xylitol; commonly used as sweeteners.

What is glycoside formation and what is its effect on the anomeric carbon?

Glycoside formation occurs when the anomeric hydroxyl reacts with an alcohol to form an O-glycosidic bond; this makes the anomeric carbon non-reducing; glycosides are stable in base and resistant to oxidation and are crucial in forming disaccharides, oligosaccharides, and polysaccharides.

What is esterification in monosaccharides and give examples relevant to metabolism?

Hydroxyl groups react with acids to form phosphate esters; examples: glucose-6-phosphate, fructose-1,6-bisphosphate; key intermediates in glycolysis.

What is isomerization in monosaccharides and what kinds of interconversions occur?

Isomerization includes interconversion between aldose and ketose forms and epimers (differing at a single chiral center); mutarotation occurs via an enediol intermediate.

What are carbohydrates and their general formula?

Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen; general formula (CH2O)n with n ≥ 3; they are a primary source of energy for the body.

In solution, which form predominates for monosaccharides, open-chain or cyclic?

Cyclic forms predominate in aqueous solutions.

What is the anomeric carbon and when is it formed?

The anomeric carbon is the new chiral center formed at the former carbonyl carbon during cyclization.