Galactose

Galactose is a type of simple sugar called a monosaccharide. It is often called gal for short. This sugar looks like a white solid that can dissolve in water.

Galactose is very close in taste to another sugar called glucose, being about 80 to 90 percent as sweet. It is also a bit less sweet than table sugar, known as sucrose, being about 65 percent as sweet.

This sugar is important in our bodies because it is a building block for a bigger sugar called lactose, which we find in milk. Without galactose, many of us would not be able to enjoy dairy products the way we do.

Occurrence

Galactose is a simple sugar found in nature. It is part of a substance called galactan, which is found in plant materials and is made of long chains of galactose.

Galactose is sometimes called "brain sugar" because it is found in special molecules in nerve tissue. It can also be found in certain bacteria, fungi, and tiny organisms.

When galactose joins with another sugar called glucose, they form a compound known as lactose, which is the main sugar found in milk. Our bodies have special tools called enzymes that help break down lactose back into galactose and glucose so we can use it. This process is important for getting energy from the food we eat, especially from dairy products.

Structure and isomerism

Galactose can be found in two different shapes: an open chain and a ring shape. In the open-chain shape, it acts like an aldehyde.

There are four ring shapes of galactose. Two of these rings have six parts, called pyranose, and two have five parts, called furanose. Each ring shape can also change to have two different setups, called alpha and beta, because a new point of difference forms when the ring closes. In the six-part ring shape, a specific group sits in a certain position on the third part of the chain.

Metabolism

Glucose is more stable than galactose and doesn't easily form certain molecules with proteins or fats. Because of this, many living things have a quick way to change galactose into glucose.

The main way our bodies process galactose is called the Leloir pathway. This pathway changes galactose into a form the body can use for energy. It uses special proteins called enzymes to do this step by step.

If someone can't use the Leloir pathway properly due to a genetic change, even small amounts of galactose can be harmful. This condition is known as galactosemia.