Protein structure and function II

Myoglobin

A monomeric, globular protein in muscle which binds oxygen with high affinity

Haemoglobin

A tetrameric protein in red blood cells which transports oxygen

Bohr effect

An increase of H+ concentrations lowers the pH and CO2 concentration reduces the affinity of haemoglobin for oxygen

Tissues with high metabolism produces CO2 and acids which requires oxygen

H+ and CO2 bind to haemoglobin and lowers oxygen affinity

Differences between myoglobin and haemoglobin

Myoglobin is a monomer

Myoglobin stores oxygen

Haemoglobin is a tetramer

Haemoglobin transports oxygen

Haemoglbin binds oxygen cooperativley

Binding of oxygen to haemoglobin can be regulated

Evolution of globin proteins

Sickle cell anaemia

Glu6—> Val in the beta chain of haemoglobin

The new valine side chain can bind to a different haemoglobin molecules to form a strand

This will sickle the red blood cell

The sickled blood cells clog small capillaries and impair blood flow because of the long haemoglobin fibres

This will result in painful swellings and a high risk of a stroke

Sickle cell trait and malaria

Untreated homozygous individuals generally die in childhood

Heterozygous individuals exhibit a resistance to malaria

The parasite ‘plasmodium falciparum’ which causes malaria lives within red blood cells at one stage in its life cycle

Fibrous proteins

Provides strenght and flexibility

alpha-keratin is an essential component of hair, skin and feathers

Collagen is the most abundant protein found in mammels. It is am extracellular protein and is a main fibrous component of skin, bone, teeth, tendon and cartilage

What does collagen form

Forms a triple helix

The collagen helix is a unique secondary structure, distinct from the alpha-helix

4-hydroxyproline

Contains a hydroxyl group

It is needed for the structure of collagen

Proline is converted to 4-hydroxyproline after collagen has been synthesized

The yellow dashes represent covalent bond forming between the alpha helix