Haemoglobin
Definition
The iron-containing oxygen-transport protein in red blood cells, composed of four polypeptide subunits each with a haem prosthetic group. Its pseudoperoxidase activity makes it the target molecule of presumptive blood tests. Species-specific differences in haemoglobin structure are exploited by immunochromatographic strips that distinguish human from animal blood.
- Type
- Iron-containing protein in red blood cells
- Primary function
- Carries oxygen throughout the body
- Forensic application
- Basis for presumptive blood tests and bruise age estimation
- Breakdown products
- Methaemoglobin and haemichrome, visible as color change from red to brown
Common questions
What does haemoglobin do in the body?+
Haemoglobin is an iron-containing protein found in red blood cells. Its main job is to carry oxygen from your lungs to cells throughout the body. In forensic work, we care about it because it behaves predictably when blood stains age or when tissues are damaged.
Why is haemoglobin important in blood testing?+
Haemoglobin has peroxidase-like activity, meaning it can trigger chemical reactions that detect blood at a crime scene. Most presumptive blood tests rely on this property. When blood stains age, haemoglobin breaks down into methaemoglobin and haemichrome, which is why old bloodstains change color from red to brown.
How does haemoglobin breakdown help estimate bruise age?+
When blood vessels rupture and cause a bruise, haemoglobin is released into surrounding tissue. It then undergoes a predictable, though variable-timed breakdown. Forensic scientists study this color change to estimate when the bruise occurred, though the timing is not always precise.
Related terms
- Amino Acid
- The monomer unit of proteins. All 20 standard amino acids share a central carbon bonded to an amino group, a carboxyl group,...
- Bilirubin
- A yellow-orange breakdown product of biliverdin, seen as the yellow-brown phase of a resolving bruise. Its appearance indicates advancing haemoglobin degradation.
- Biliverdin
- A green breakdown product of haemoglobin, appearing as the blue-green phase of bruise colour change. Biliverdin is then converted to bilirubin.
- Cross-Polarised Photography
- A photographic technique using polarising filters on both the light source and the camera lens to eliminate surface glare and reveal subsurface...
- Haematocrit
- The proportion of blood volume occupied by red blood cells, approximately 45% in adult males and 40% in adult females. Influences the...
- Haemolysis
- The rupture of red blood cells and release of haemoglobin into the surrounding fluid. In casework, haemolysis of aged stains, wet stains,...
- Isoenzyme (Isozyme)
- Multiple molecular forms of the same enzyme that differ in amino acid sequence but catalyse the same reaction. In forensic serology, isoenzyme...
- Methaemoglobin
- An oxidised form of haemoglobin in which ferrous iron (Fe2+) is converted to ferric iron (Fe3+), unable to carry oxygen. Its formation...
- Oxyhaemoglobin
- The form of haemoglobin in freshly shed arterial blood, where iron in the haem group is in the ferrous (Fe²⁺) state and...
- Peroxidase
- An enzyme that catalyses the transfer of oxygen from hydrogen peroxide to an electron donor, often producing a coloured product. Haemoglobin has...
- Plasma
- The liquid fraction of blood (approximately 55% by volume), containing water, proteins (albumin, immunoglobulins, fibrinogen, clotting factors), electrolytes, glucose, hormones, and dissolved...
- Protein Denaturation
- The loss of a protein's three-dimensional structure without breaking peptide bonds, caused by heat, pH change, UV radiation, or chemical agents such...
Explained in these topics
- Ageing of Bruises: Methods and LimitationsThe iron-containing protein in red blood cells that carries oxygen. When vessels rupture in a bruise, haemoglobin is released into tissue and undergoes a predi...
- Composition and Properties of BloodThe iron-containing protein in red blood cells that carries oxygen. Its peroxidase-like activity is the basis of most presumptive blood tests; its oxidative de...
- Proteins and Enzymes in Biological EvidenceThe iron-containing oxygen-transport protein in red blood cells, composed of four polypeptide subunits each with a haem prosthetic group. Its pseudoperoxidase...