Study guides › B/B › Biochemistry
Carbohydrates
Sugars are fuel, structure, and recognition signals. You will learn monosaccharide stereochemistry, ring forms and anomers, the reactions that define reducing sugars, glycosidic bonds in disaccharides and polysaccharides, and glycoproteins.
Study this chapter in PrepMed (free)
What this chapter covers
- Monosaccharides & Stereochemistry. Sugar questions are stereochemistry questions: D versus L, epimers versus enantiomers, and how many stereoisomers exist.
- Ring Forms, Anomers & Mutarotation. In water sugars are mostly rings, and the alpha versus beta anomeric carbon explains a lot of carbohydrate behavior.
- Reactions of Sugars & Reducing Sugars. Benedict and Tollens tests reveal whether a sugar can open to a free carbonyl, which separates reducing from nonreducing sugars.
- Glycosidic Bonds, Disaccharides & Polysaccharides. Whether a linkage is alpha or beta decides if humans can digest a polysaccharide and whether it stores energy or gives structure.
- Glycoproteins & Glycoconjugates. Sugars attached to proteins and lipids act as address labels, and the MCAT asks where, how, and why they are attached.
Key points to know
- Aldose = aldehyde; ketose = ketone (usually at C2)
- D/L is set by the highest-numbered stereocenter (OH right = D)
- Hemiacetal or hemiketal formation gives the ring
- α = anomeric OH trans to CH₂OH; β = cis
- Reducing sugar = free hemiacetal or hemiketal anomeric carbon
- Tollens (Ag) and Benedict (Cu²⁺) tests detect reducing sugars
- Glycosidic bond = acetal joining anomeric carbon to –OH
- Maltose α(1→4), cellobiose β(1→4), lactose β(1→4), sucrose α(1→2)β
Try a practice question
D-glucose and D-galactose differ only in configuration at C4. What is the relationship?
- Enantiomers
- Anomers
- Epimers
- Constitutional isomers
Show the answer
C. Two diastereomers that differ at exactly one stereocenter are epimers. Enantiomers would differ at all four centers, and anomers differ at the anomeric carbon of the ring form.
Common questions
What does this chapter cover?
Carbohydrates covers Monosaccharides & Stereochemistry, Ring Forms, Anomers & Mutarotation, Reactions of Sugars & Reducing Sugars, Glycosidic Bonds, Disaccharides & Polysaccharides, Glycoproteins & Glycoconjugates.
What should I know first?
Aldose = aldehyde; ketose = ketone (usually at C2) D/L is set by the highest-numbered stereocenter (OH right = D) Hemiacetal or hemiketal formation gives the ring
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.