Final answer:
Insulin and growth factors act on b. tyrosine kinase receptors, which mediate their effects through phosphorylation of tyrosine residues on target proteins leading to various cellular responses such as increased glucose uptake.
Step-by-step explanation:
Insulin and growth factors act on b. tyrosine kinase receptors. When insulin binds to its receptor, which is a type of tyrosine kinase receptor, the receptor forms a dimer and the insulin molecule is internalized in the cytoplasm.
This process involves the activation of the tyrosine kinase enzyme, leading to the phosphorylation of specific tyrosine amino acids in target proteins like IRS-1, which ultimately increases the uptake of glucose by activating glucose transporters like Glut4.
Growth factors, such as nerve growth factor (NGF) and epidermal growth factor (EGF), also stimulate growth and differentiation through receptor tyrosine kinase-mediated signal transduction.
In this process, the intracellular activity occurs within the cytoplasmic domain of the receptor itself, again leading to the phosphorylation of tyrosines on target proteins.