Question

Explain the cell signaling pathway which involves membrane receptor (tyrosine kinase receptors and G protein-coupled receptors). Use ONE (1) specific example to explain each reception pathway.                                   

The details of the summary should be concise and informative. The length of the summary for each type of membrane receptor should be less than 200 words.   

Answer 1

RECEPTOR TYROSINE KINASE

The growth and divison of epidermal cell and epithelial cells is stimulated by epidermal growth factor(EGF). EGF is primary messanger that initiates the EGF signal transduction pathway

EGF binds to EGF receptor in the unbound state, the EGF consist of two identical but separated by monomeric units. Each monomer contain ,a binding site for EGF on the extracellular site, and a tyrosine kinase domain on the intracellular site

when total of the two EGF molecule bound to the extracellular region, they induce the dimerrization arm of one monomer to stretch into second monomer, which leads to the formation of the dimer

when conformational changes occur, the carbonyl terminal end of one tyrosine kinase domain moves into the active site of opposing tyrosine kinase domain. this phosphorylates the C terminal

1. the phosphorylated region of EGF receptor act as an anchor for an adaptor ptotein called GRB-2
2. Grb-2 recruit another protein called Sos
3. Sos then binds . Ras a smal G protein. this activates Ras by expelling a GDP and binding a GTP
4. ras activates Raf
5. Raf activates protein kinase called MEK
6. activated MEK in turn activate extracellular signal regulated kinases (ERKs)
7. activated ERKs move into nucleus and stimulate transcriptional factor to increase gene expression . this increase rate of protein synthesis, which enlarges cytoskelton and leads to cell growth

G PROTEIN COUPLED RECEPTOR

G protein are also known as seven transmembrane helic receptor

in case of epinephrine signal transduction pathway it binds to beta adrenergic receptor. the beta andrenergic receptor contains a heterotrimeric domain on the intracellular side consisting of an alpha, beta and gamma domains. the alpha domain is a G protein because it binds guanyl nucleotides

Upon binding the epinephrine induces conformational changes in the 7 transmembrane that stimulates the G protein to release GDP and bind GTP, This also causes the beta dimer to dissociate from the G alpha protein

a signal epinephrine can cause many G protein to exchange of GTP for GDP. this creates an amplified effect

the dissociated G alpha domain in the GTP state moves and binds to another transmembrane protein called adenylate cyclase. it simulate adenylate cyclase to begin transforming ATP to cAMP. the cAMP molecules are secondary messanger. this lead to second level oF amplification

cAMP further activates the protein kinase A. PROTEIN KINASE goes on to phosphorylate target molecule which activate many different process. for instance. PKA activate enzymes that stimulate glycogen metabolism and stimulate gene expression by activating transcription factors