Question

or each of the following sentences, select the best word or phrase from the list below to fill in the blanks ot all words or phrases will be used; each word or phrase should be used only once 38. (3) An extracellular signal molecule can act to change a cell's behavior by acting through cell that control intracellular signaling proteins. These intracellular proteins that bring surface signaling proteins ultimately change the activity of about cell responses. Intracellular signaling proteins can received to evoke a strong response from just a few extracellular signal molecules. A cell that receives more than one extracellular signal at the same time can information using intracellular signaling proteins molecular switches, letting a cell know that a signal has been received. Enzymes that phosphorylate proteins, termed these enzymes are countered by the activity of the signal this proteins can act as can also serve as molecular switches; the actions of GMP-binding GTP-binding phosphatases neurotransmitter amplify acetylase cleavage decouple sterols convolute kinases autocrine effector decrease esterases integrate AMP-binding receptors 39. (3) G-protein-coupled receptors (GPCRs) all have a similar structure with transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G protein, composed of protein subunits are tethered to the plasma membrane by short lipid tails. When unstimulated, the a subunit is bound to stimulation. The intrinsic inactivating the G protein keeping the subunit in an active state of the G- subunits, becomes activated on which is exchanged for activity of the a subunit is important for inhibits this activity of the a subunit, thereby ATP GTPase Phosphodiesterase GTP seven four GDP diacylglycerol ive adenylyl cyclase cholera toxin AMP three ATPase twelve cAMP two Bonus: Ask and answer one of your own questions

Answer 1

38 (3) An extracellular signal molecule can act to change a cell's behavior by acting through cell surface receptors that control intracellular signaling proteins. (Cell surface receptors are protein molecules present on the cell surface that can specifically bind to an extracellular signal molecule which will cause conformational changes in the receptor and evoke intracellular response).

These intracellular signaling proteins ultimately change the activity of the effector proteins that bring about cell responses.

Intracellular signaling proteins can amplify the signal received to evoke a strong response from just a few extracellular signal molecules.

A cell that receives more than one extracellular signal at the same time can integrate this information using intracellular signaling proteins.

GTP-binding proteins can act as molecular switches, letting a cell know that a signal has been received.

Enzymes that phosphorylate proteins, termed kinases, can also serve as molecular switches; the actions of these enzymes are countered by the activity of phosphatases.

(Explanation: This is an example of signal transduction through GPCRs, one of the largest cell surface receptors. GPCRs stand for G protein coupled receptors implying that they act through activation of G proteins, which serves as a molecular switch to turn intracellular signaling. GPCRs are seven transmembrane proteins with an N-terminus and three extracellular loops outside the cell membrane, seven transmembrane regions in the plasma membrane, & three intracellular loops & C-terminus in the cytoplasm. The extracellular region of the receptor catches the specific extracellular signal which cause conformational changes in the receptor and through the intracellular region activates the G protein (where GDP is released and exchanges for GTP). The activated G-protein (GTP bound) due to conformational change is now able to bind to effector protein which produces large number of second messengers which evoke cellular response. The timing and duration of the signal can also be modulated by other class of activating proteins called kinases (which activate effector proteins by phosphorylation) which are also activated due to cellular signaling. Another class of proteins called phosphatases can act as inhibitors which counteract the role of kinases by dephosphorylating effector proteins).

39. (3) G-protein-coupled receptors (GPCRs) all have a similar structure with seven transmembrane domains. When a GPCR binds an extracellular signal, an intracellular G proteins composed of three subunits, becomes activated. Two of the G-proteins are tethered to the plasma membrane by short lipid tails. When unstimulated, the alpha subunit is bound to GDP which is exchanged for GTP on stimulation. The intrinsic GTPase activity of the alpha subunit is important for inactivating the G-protein. Cholera toxin inhibits this activity of the alpha subunit, thereby keeping the subunit in an active state.

(Explanation: Already explained above about G protein mediated signalling. GTPase activity is the cleavage of the terminal phophate bond of GTP (to GDP) with the help of water or in other words it is hydrolysis of GTP to GDP. This intrinsic GTPase activity is found in the alpha subunit of the G protein. In its inactive form i.e. GDP bound, it exists as a heterotrimer (alpha, beta and gamma subunits together). However, once exchanged for GTP during activation, beta and gamma subunits dissociate from the GTP bound alpha subunit and initiate intracellular signaling).