Lecture 11 Flashcards
(27 cards)
What is the basic definition of a carbohydrate?
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen with the general formula (CH₂O)n. They are also called sugars or saccharides.
What are the simplest carbohydrates called?
Monosaccharides (simple sugars).
What are the polymers of carbohydrates called?
Polysaccharides or glycans.
What are the three major biological roles of carbohydrates?
- Energy storage – e.g., glucose and starch
- Structural components – e.g., cellulose in plants, chitin in arthropods
- Protein modification – e.g., glycoproteins in antibodies
What are the key functional groups in monosaccharides?
Alcohol (-OH) groups (polyalcohols)
Aldehydes (-CHO) (in aldoses)
Ketones (C=O) (in ketoses)
How do aldehydes and ketones differ structurally?
Aldehydes have a hydrogen (-H) attached to the carbonyl carbon.
Ketones have two carbon groups attached to the carbonyl carbon.
How are monosaccharides classified based on carbon chain length?
Trioses (3C) – e.g., glyceraldehyde
Tetroses (4C) – e.g., erythrose
Pentoses (5C) – e.g., ribose
Hexoses (6C) – e.g., glucose, fructose
What is a chiral center in a monosaccharide?
A carbon atom bonded to four different groups.
What suffix is used in the names of most sugars?
The suffix ”-ose” (e.g., glucose, fructose).
How are enantiomers related to each other?
Enantiomers are mirror images of each other at all chiral centers.
What is the D- and L- system in sugar stereochemistry?
D-sugars have the -OH on the right at the highest-numbered chiral carbon.
L-sugars have the -OH on the left.
(D-sugars predominate in nature!)
How are diastereomers different from enantiomers?
Diastereomers are stereoisomers that are not mirror images.
How is the Fischer projection drawn?
The carbonyl (C=O) is at the top.
The vertical bonds go behind the plane.
The horizontal bonds come out toward the viewer.
What do the D- and L- configurations mean in a Fischer projection?
D-sugars: The hydroxyl (-OH) on the highest chiral carbon is on the right.
L-sugars: The hydroxyl (-OH) on the highest chiral carbon is on the left.
What happens when a monosaccharide undergoes hemiacetal/hemiketal formation?
It cyclizes, forming a ring structure.
What happens when alcohols react with aldehydes and ketones?
They form hemiacetals (from aldehydes) and hemiketals (from ketones).
Why do monosaccharides form rings?
Because five- and six-membered rings are the most stable.
What is the anomeric carbon?
The carbon that was originally the carbonyl carbon and became a new chiral center in the ring.
What are the two main cyclic forms of sugars?
Pyranose (6-membered ring, like glucose)
Furanose (5-membered ring, like fructose)
What are anomers?
Stereoisomers that differ only at the anomeric carbon.
How do α- and β-anomers differ?
α-anomer: The -OH on the anomeric carbon is down (opposite side from CH₂OH).
β-anomer: The -OH on the anomeric carbon is up (same side as CH₂OH).
What is the Haworth projection?
A simplified drawing of cyclic sugars that makes it easy to see stereochemistry.
What is the chair conformation of sugar rings?
The most accurate 3D structure, where β-D-glucopyranose has all its bulky groups in equatorial positions.
What happens when anomers are in solution?
They interconvert through the linear form in a process called mutarotation.
