Glucose and galactose are two monosaccharides. They both contain 6 carbon atoms and an aldehyde group. 

Galactose is an isomer of glucose. Both have the same structure except for the organization of their atoms. The main structural difference between the two is the position of the –OH group at the 4thcarbon atom.  

• In glucose, the –OH group of the 4thcarbon is directed towards the right side.
• In galactose, the –OH group of the 4thcarbon is directed towards the left side. 

This structural difference results in several other differences between glucose and galactose: 

• Stability: Glucose is more stable than galactose
• Melting point: Glucose has a lower melting point than galactose
• Taste: Glucose is sweeter than galactose