Final answer:
The question revolves around the role of Protein Tyrosine Kinases (PTK) in cellular functions through the phosphorylation of tyrosine residues in proteins, distinguishing them from other kinases like PKA and PKC, which phosphorylate serine or threonine residues. Tyrosine kinase receptors are involved in cell signaling, particularly in response to extracellular ligands like growth factors, while phosphorylation states can regulate numerous cellular processes, including metabolic pathways and gene transcription.
Step-by-step explanation:
The question refers to Y containing proteins that include Protein Tyrosine Kinases (PTK). Proteins that contain tyrosine kinase domains are involved in signaling pathways which regulate a variety of cellular processes. Tyrosine kinases phosphorylate the amino acid tyrosine in protein substrates, which can modulate the activity of these proteins.
Protein kinase A (PKA) and Protein kinase C (PKC) are types of serine-threonine kinases that add phosphate groups to serine or threonine, rather than tyrosine. The phosphorylation state of a protein can affect many cellular functions, such as its activity, interaction with other proteins, and location within the cell. For instance, PKC, upon phosphorylating the inhibitor protein IK-B, allows the regulatory protein NF-kB to enter the nucleus and initiate RNA transcription. This is an example of how phosphorylation can regulate the activity of proteins and, consequently, cellular metabolism and responses.
Furthermore, tyrosine kinase receptors are membrane-spanning proteins that are involved in the reception of extracellular signals like insulin or growth factors. These receptors, when activated by their ligands, phosphorylate each other, providing sites for further signal transduction inside the cell. The equilibrium constant (k) of a ligand-receptor system affects the likelihood of ligand binding.
Lastly, the effect of phosphorylation is not uniform and depends on the specific site and context; this can mean activation or inactivation of enzymes, as seen with enzyme X potentially activated by phosphorylation at one serine residue but deactivated at another. The Arabidopsis Information Resource (TAIR) gene ontology (GO) and the Plant Protein Phosphorylation DataBase (P3DB) provide resources that help to track proteins and phosphorylation events.