Question

First, describe in general terms a cell signaling response that ends in A) a cytoplasmic response and B) a nuclear response. Use the following terms in this description: response, primary signal molecule, transduction pathway, receptor. Second, describe in detail the EGF map kinase pathway as an example of the nuclear response and the epinephrine-glycogen phosphorylase pathway as an example of the cytoplasmic response.    Appropriately use the following in your answer to the second part of the question: G protein receptor, tyrosine kinase receptor, secondary messenger, cyclic AMP, adenylyl cyclase, protein phosphorylation cascade, Ras, EGF hormone, epinephrine, protein kinase A, myc, jun, cyclins, transcription factor, G protein.   When using the above terms make sure you point out when they are examples of the following: secondary messengers, signal molecules, cytoplasmic responses, nuclear responses, transduction pathways, receptors.

Answer 1

Cellular activities gets altered by signal transduction pathways, as it modifies the regulation of the cell. Such changes or responses takes place in cytoplasm or nucleus of the cell, refers to cytoplasmic or nuclear responses, respectively. Phosporylation reaction is stimulated by a signaling molecule, when it is phosporylated the last kinase of the sequence enters the nucleus and activates gene regulating protein. That protein in turn stimulates transcription and the resulting mRNA initiates synthesis of protein in the cytoplasm.

EGF map kinase pathway When the signaling molecules binds with the cell surface and it ends when the DNA in the nucleus expresses a protein that produces change in the signal in nuclues. Lets see the process in detail below.

EGF gets activated by extracellular ligands, EGF binds with EGF receptors and activates tyrosine kinase activity. When EGFR becomes phosphorylated, GRB2 binds with phosphotyrosine residues. GRB2 binds with guanine nucleotide exchange factor SOS, since GRB2 has two domains of SH3. Docking takes place between binded GRB2-SOS complex with EGFR. This in turn will activate Ras family, these phosphate signals enters nucleus of the cell and causes transcription of DNA and synthesis of protein.

Epinephrine-glycogen phosphorylase pathway Glycogen phosphorylase is the process of glycogen synthesis. Glycogen phosphorylase gets activated by phosphorylation. Epinephrine gets binds with receptor protein which activates adenylate cyclase, leads to formation of cyclic AMP from ATP molecules. Cyclic AMP binds with protein kinase A, hence it will get ditached from the assembly and phosphorylate other proteins.