Hemoglobin facts for kids

Structure of human hemoglobin.
The α and β subunits are in red and blue.
The iron-containing heme groups in green

Hemoglobin (or haemoglobin) is a protein in red blood cells which contains iron. It is used to transport oxygen around the human body. Hemoglobin is found in the red blood cells of all vertebrates apart from white-blooded fish. It also occurs in some invertebrates.

Hemoglobin is involved in the transport of other gases. It carries some of the body's respiratory carbon dioxide (about 20-25% of the total).

Red blood cells get their color from hemoglobin, which is red. There are millions of hemoglobin molecules in each red blood cell and millions of red blood cells in the human body. When hemoglobin has oxygen attached, it is called oxyhemoglobin.

Structure

The most common type of hemoglobin in mammals contains four such subunits. Each subunit of hemoglobin is a globular protein (globin) with a heme group inside it. Each heme group has one iron atom. This binds one oxygen molecule. So the complete hemoglobin molecule has four globin chains, four heme molecules, and four iron atoms. When hemoglobin is in the lungs, it picks up oxygen in its hemes, and carries it to the rest of the body.

Its structure took years to work out. Max Perutz and John Kendrew worked out the structure of myoglobin first. That muscle globin is smaller, with only one heme group.

Diagnostic uses

A hemoglobin concentration measurement being administered before a blood donation at the American Red Cross Boston Blood Donation Center.

Hemoglobin concentration measurement is among the most commonly performed blood tests, usually as part of a complete blood count. For example, it is typically tested before or after blood donation. Results are reported in g/L, g/dL or mol/L. 1 g/dL equals about 0.6206 mmol/L. Normal levels are:

• Men: 13.8 to 18.0 g/dL (138 to 180 g/L, or 8.56 to 11.17 mmol/L)
• Women: 12.1 to 15.1 g/dL (121 to 151 g/L, or 7.51 to 9.37 mmol/L)
• Children: 11 to 16 g/dL (110 to 160 g/L, or 6.83 to 9.93 mmol/L)
• Pregnant women: 11 to 14 g/dL (110 to 140 g/L, or 6.83 to 8.69 mmol/L) (9.5 to 15 usual value during pregnancy)

Images for kids

• 

  Max Perutz won the Nobel Prize for chemistry for his work determining the molecular structure of hemoglobin and myoglobin

• 

  Protein alignment of human hemoglobin proteins, alpha, beta, and delta subunits respectively. The alignments were created using UniProt's alignment tool available online.

• 

  A schematic visual model of oxygen-binding process, showing all four monomers and hemes, and protein chains only as diagrammatic coils, to facilitate visualization into the molecule. Oxygen is not shown in this model, but, for each of the iron atoms, it binds to the iron (red sphere) in the flat heme. For example, in the upper-left of the four hemes shown, oxygen binds at the left of the iron atom shown in the upper-left of diagram. This causes the iron atom to move backward into the heme that holds it (the iron moves upward as it binds oxygen, in this illustration), tugging the histidine residue (modeled as a red pentagon on the right of the iron) closer, as it does. This, in turn, pulls on the protein chain holding the histidine.

• 

  A hemoglobin concentration measurement being administered before a blood donation at the American Red Cross Boston Blood Donation Center.

• 

  The giant tube worm Riftia pachyptila showing red hemoglobin-containing plumes

• 

  Heart of Steel (Hemoglobin) (2005) by Julian Voss-Andreae. The images show the 5-foot (1.50 m) tall sculpture right after installation, after 10 days, and after several months of exposure to the elements.

See also

In Spanish: Hemoglobina para niños