Carbohydrates

What is the general formula of carbohydrates?

(CH₂O)ₙ

What are the three main roles of carbohydrates in biological systems?

Energy storage, structural support, and cellular recognition/signaling

Name two structural carbohydrates.

Cellulose (plants) and chitin (exoskeletons).

What is a reducing sugar?

A sugar that can be oxidized, typically containing a free aldehyde or ketone group

What reagent is used to test for reducing sugars?

Benedict's reagent.

What are the three classes of carbohydrates based on size?

Monosaccharides, oligosaccharides, and polysaccharides.

What is the difference between an aldose and a ketose?

Aldoses have an aldehyde group; ketoses have a ketone group

What is the generic name for a sugar with 5 carbon atoms and an aldehyde group?

Aldopentose

What does the Fischer projection represent?

A 2D representation of a 3D sugar structure, showing stereochemistry.

What energy yields result from glucose metabolism under aerobic and anaerobic conditions?

Aerobic: −2880 kJ/mol; Anaerobic: −75 kJ/mol.

What industrial applications use carbohydrates?

Fermentation (e.g., brewing, baking), food gelling agents (e.g., pectin), medical uses (e.g., hyaluronic acid), and sustainable chemical production.

What determines the specific identity of a sugar molecule?

The stereochemistry at its chiral centers

What determines whether a sugar is a D- or L-isomer?

The orientation of the OH on the chiral carbon furthest from the carbonyl group

What are enantiomers?

Stereoisomers that are non-superimposable mirror images of each other.

What are epimers?

Diastereoisomers that differ in configuration at only one stereocentre.

What are diastereoisomers?

Stereoisomers that are not mirror images and differ at two or more chiral centers

What is a hemiacetal and how is it formed in sugars?

A hemiacetal forms when a hydroxyl group attacks an aldehyde group within the same sugar molecule.

What are α- and β-anomers?

Isomers that differ in configuration at the anomeric carbon; α = OH down, β = OH up in Haworth projection.

What is mutarotation?

The interconversion between α- and β-anomers in solution through the open-chain form.

What are furanoses and pyranoses?

Furanoses are 5-membered rings; pyranoses are 6-membered rings formed by cyclic sugars

What is the most stable chair conformation of β-D-glucose?

The one where all hydroxyl groups occupy equatorial positions

What distinguishes glucose from galactose structurally?

The configuration at carbon 4 (C4).

What structural feature defines a sugar as a pyranose?

A six-membered ring formed via hemiacetal linkage

Name two important biologically modified sugars

Glucosamine and glucuronic acid