Enzyme-linked Receptors (Wiki)
(They) are found in all living species. They have two important domains, an
extra-cellular ligand binding domain and an intracellular domain, which
has a Catalytic function; and a transmembrane helix. The signaling
molecule binds to the receptor outside of the cell and causes a
conformational change on the Catalytic function located on the receptor
inside of the cell."
"Examples of the enzymatic activity include:
As far as I can tell, Wikipedia doesn't provide a diagram for the structure of enzyme linked receptors. However, there are two small diagrams at:
Unfortunately, it doesn't expand when you click on it, so it's a bit hard to read.
The accompanying text is:
"The study of various growth factors (extracellular signal proteins that regulate growth) shone a light on enzyme-linked receptors when it was discovered that they utilized these receptors. The responses to growth factors are typically much slower (on the order of hours) than responses connected to the other two families of cell-surface receptors. Although, recent studies have begun to connect enzyme-linked receptors to direct effects on the cytoskeleton, envolving cell movement and change of shape. Enzyme-linked receptors only span the membrane once (as opposed to seven times for G-protein-linked receptors). The internal side of the receptor acts as an enzyme, which is activated when the appropriate ligand binds to the external portion of the receptor. The largest class of receptors with this family act as tyrosine protein kinases, which phosphorylate tyrosine side chain residues on selected intracellular proteins. Such receptors are called receptor tyrosine kinases. Their function is essentially quite simple. The binding of a signal to the outer-membrane portion causes the internal kinase to switch on and begin phosphorylating cellular proteins. These phosphorylated proteins will go on to affect responses to the original signal."
Wikipedia does provide an explanation of 'tyrosine kinases':
"A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a tyrosine residue in a protein. Tyrosine kinases are a subgroup of the larger class of protein kinases. Phosphorylation of proteins by kinases is an important mechanism in signal transduction for regulation of enzyme activity." "Protein kinases are a group of enzymes that possess a catalytic subunit which transfers the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. The enzymes fall into two broad classes, characterised with respect to substrate specificity: serine/threonine specific and tyrosine specific"
ATP, mentioned above, is the spark of life.
Adenosine triphosphate: ATP (Wiki)
This may repeat what's already been said in another part of this web page, but ATP is so important, it's worthy of the repetition.
The 'P's in the diagram, above, are phosphorus atoms while the 'O's are oxygen atoms. Single lines between atoms indicate single valence bonds while double lines indicate double bonds. The combination of phosphorus and oxygen atoms, shown above, are referred to as "phosphate groups". As you can see, there are three of them, hence the 'triphosphate' part of ATP. The more complex structure on the right is adenosine. The phosphate groups are numbered out from the adenosine, so that the phosphate group on the far left is called the 'third phosphate'. It is the link to this third phosphate which is called "the high-energy phosphate bond" and which is, truely, the spark of life.