Question

Compare the chemical structures of lactose and sucrose.
lactose
sucrose
has 12 carbon and 11 oxygen atoms
is a disaccharide
contains the monosaccharide fructose

Answer 1

Short answer first
- Both lactose and sucrose are disaccharides with the molecular formula C12H22O11 (so each has 12 carbon and 11 oxygen atoms).
- Lactose = glucose + galactose (no fructose).
- Sucrose = glucose + fructose (contains fructose).

More detail (structural differences)
- Monosaccharide composition
- Lactose: β-D-galactopyranose linked to D-glucose (galactose + glucose).
- Sucrose: α-D-glucopyranose linked to β-D-fructofuranose (glucose + fructose).

- Glycosidic linkage and ring forms
- Lactose: β-1→4 linkage (β-D-galactopyranosyl-(1→4)-D-glucopyranose). Both residues are pyranose rings.
- Sucrose: α-1→2 linkage between the anomeric carbons (α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside). Glucose is pyranose, fructose is furanose.

- Reducing behavior
- Lactose is a reducing sugar (free anomeric carbon on the glucose unit).
- Sucrose is non-reducing (both anomeric carbons are tied up in the glycosidic bond).

- Biological/functional notes
- Lactose: found in milk; hydrolyzed by lactase into glucose + galactose.
- Sucrose: table sugar from cane/beet; hydrolyzed by sucrase/invertase into glucose + fructose.

If you want, I can draw simplified structural formulas or show the exact ring-to-ring bond positions.