Fructose

Fructose is a six-carbon monosaccharide sugar (C₆H₁₂O₆) commonly known as "fruit sugar." It is an isomer of glucose with a slightly different structure (fructose is a ketohexose), and it is found in fruits, honey, and as part of the disaccharide sucrose (table sugar).

• Fructose, glucose, and galactose all have the same molecular formula C₆H₁₂O₆ but different structures. Fructose has a ketone functional group (it's a ketose), whereas glucose is an aldose.
• Dietarily, fructose is abundant in fruit and honey, and it combines with glucose to form sucrose (table sugar). When you digest sucrose, you get one glucose and one fructose molecule.
• Fructose is primarily metabolized in the liver. It enters glycolysis after being converted to intermediates (bypassing the main glucose regulatory step), which is why excessive fructose intake is linked to fatty liver and metabolic issues - a notable fact for advanced understanding.

• If a question mentions "fruit sugar" or a sugar found in honey and fruit juices, that's fructose. Also, any question about sucrose being made of two monosaccharides expects the answer "glucose and fructose."
• Exam tricks may involve knowing fructose vs glucose differences. For example, a question might describe a sugar that is a ketose and ask which sugar it is - fructose is the classic ketohexose to identify.
• Fructose might come up in human biology contexts: e.g., "Which sugar do sperm cells use for energy in seminal fluid-" The answer is fructose (a fact often noted in physiology). Recognize that this is different from glucose being the main blood sugar.