Haemocyanin facts for kids

Single oxygenated hemocyanin molecule of an octopus: note the two Cu atoms

The underside of the carapace of a red rock crab (Cancer productus). The purple colour is caused by haemocyanin

Haemocyanin (say: HEE-mo-SY-uh-nin), also spelled hemocyanin, is a special kind of protein. It helps carry oxygen around the bodies of some animals that don't have backbones. These animals are called invertebrates.

Unlike humans and other animals with red blood, haemocyanin makes the blood of these creatures look blue when it has oxygen. This is because it uses copper atoms to pick up and release oxygen.

What is Haemocyanin?

Haemocyanin acts like a tiny oxygen delivery truck inside certain animals. It's a large molecule that floats freely in their blood-like fluid. This fluid is called haemolymph.

It's different from hemoglobin, which is the oxygen carrier in our red blood cells. Haemocyanin isn't inside blood cells. Instead, it's dissolved directly in the haemolymph.

How Haemocyanin Works

Each haemocyanin molecule has two copper atoms. These copper atoms are very important. They are the parts that grab onto oxygen molecules.

When oxygen is available, the copper atoms bind to it. This makes the haemocyanin turn a blue-green color. When the oxygen is released to the body's tissues, the haemocyanin becomes colorless again.

Animals That Use Haemocyanin

Haemocyanin is found in two main groups of animals. These are the Mollusca and the Arthropoda.

• Molluscs include animals like snails, octopuses, squid, and clams.
• Arthropods include creatures like crabs, spiders, and scorpions.

You can often see the blue color of haemocyanin in the blood of these animals. For example, if a crab gets a cut, its blood might look bluish.

Why Not All Insects Use It

Even though insects are arthropods, most of them don't use haemocyanin to carry oxygen. This is because insects have a different way of breathing.

They have a system of tiny tubes called trachea. These tubes carry oxygen directly to their body parts and muscles. This system is very efficient for them. It means they don't need a special protein in their blood to move oxygen around.

Images for kids

• 

  A hemocyanin active site in the absence of O2 (each Cu center is a cation, charges not shown).

• 

  O2-bound form of a hemocyanin active site (the Cu2 center is a dication, charge not shown).

See also

In Spanish: Hemocianina para niños