The notch signaling pathway is a highly conserved cell signaling system present in most multicellular organisms.
Notch is present in all metazoans, and mammals possess four different notch receptors, referred to as NOTCH1

NOTCH1

Notch homolog 1, translocation-associated , also known as NOTCH1, is a human gene encoding a single-pass transmembrane receptor.A deficiency can be associated with bicuspid aortic valve....

, NOTCH2

NOTCH2

Neurogenic locus notch homolog protein 2 also known as notch 2 is a protein that in humans is encoded by the NOTCH2 gene.NOTCH2 is associated with Alagille syndrome and Hajdu–Cheney syndrome.- Function :Notch 2 a member of the notch family...

, NOTCH3

Notch 3

Neurogenic locus notch homolog protein 3 is a protein that in humans is encoded by the NOTCH3 gene.-External links:...

, and NOTCH4

NOTCH4

Neurogenic locus notch homolog protein 4 is a protein that in humans is encoded by the NOTCH4 gene.-Further reading:...

. The notch receptor is a single-pass transmembrane receptor protein. It is a hetero-oligomer composed of a large extracellular

Extracellular

In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...

 portion, which associates in a calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

-dependent, non-covalent interaction with a smaller piece of the notch protein composed of a short extracellular region, a single transmembrane-pass, and a small intracellular

Intracellular

Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...

 region..