Blue is the New Red

Fact: Shellfish have blue blood.

Cut a lobster’s main artery and it won’t bleed like you and me – their blood turns a deep blue on contact with air.

The secret behind this colourful mystery comes from one of biology’s most important proteins – hemaglobin. Hemaglobin is the protein in our red blood cells that is responsible for carrying oxygen round our body – but also for making them red.

Hemaglobin has four ‘haem’ groups, which are the bit of the protein that actually carries the oxygen. At the centre of these haem groups is an all-important iron atom, which binds to oxygen to carry it round the body. When iron is exposed to oxygen, it turns red – just think about how similar the colour of rust (iron oxide) and blood  are.

Now shellfish do have blood,but they don’t have hemaglobin. Instead, they have hemocyanin – which is pretty much the same as hemaglobin, but has copper atoms at the centre of the heam groups instead of iron atoms. Crucially, when copper is exposed to oxygen it goes blue, which is the simple reason as to why shellfish have blue blood.

In fact, its not just shellfish: snails, squids and octopuses all shun hemaglobin in favour of a healthy blue tinge. And the most famous of all – the horseshoe crab, which is coveted by scientists who catch them, take 1/3 of their blood for use in the lab and then release them. Think of it as forced blood donation.

I wouldn’t have got into Cambridge if I hadn’t pulled out this fact in my interview, so its one of my favourites.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license

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