cell-signalling-and-transduction biochemistry question and answers -Page 2

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1. The binding of ligands to many G-proteins linked receptors leads to shortlived
Options
A. increase in the concentration of certain intracellular signaling molecules called second messenger
B. decrease in the concentration of certain intracellular signaling molecules called second messenger
C. increase in the concentration of certain extracellular signaling molecules called first messenger
D. decrease in the concentration of certain extracellular signaling molecules called first messenger

2. The enzyme that catalyzes the splitting of PIP2 into two molecules of inositol triphosphate (IP3) and diacylglycerol in cell signaling, is
Options
A. phosphokinase C
B. phospholipase C
C. phosphodiesterase C
D. lipokinase

3. Which of the following statement is incorrect?
Options
A. The principal lipophilic hormones that binds to receptors located in the plasma membranes are prostaglandins
B. Prostaglandins are synthesized from arachidonic acid
C. Prostaglandins act as paracrine signaling molecules
D. None of the above

4. In paracrine signaling, the signaling molecules affects only
Options
A. target cells close to the cell from which it was secreted
B. target cells distant from its site of synthesis in cells of an endocrine organ
C. both (a) and (b)
D. none of the above

5. A signal cascade induced by adrenaline or thyroxine
Options
A. must begin with receipt of the signal molecule by a surface receptor
B. involves the activation of a G protein
C. results in the activation of a sequence of enzymes needed for the cell effect
D. all of the above

6. Self-phosphorylation is an excellent mechanism for triggering specific catalytic function of the proteins involved in signal cascades because it
Options
A. changes the shape and thus the enzymatic activity of the proteins involved
B. makes the receptor more likely to capture the signaling, molecule
C. allows hydrophilic signaling molecules to cross the plasma membrane
D. None of the above

8. When a __________ reaches its __________ , there is a specific means of receiving it and acting on the message. This task is the responsibility of specialized proteins called __________ .
Options
A. signaling molecule; receptor; G proteins
B. signaling molecule; target cell; G proteins
C. signaling molecule; target cell; receptors
D. kinase; receptor; proteases

9. Nitroglycerin has long been administered to human patients suffering from chronic chest pain (angina). This medication works because it
Options
A. mimics the action of signal receptors
B. is broken down into hormones that affect the heart
C. interferes with chemical cascades that trigger contraction of heart muscle
D. breaks down into nitric oxide, which increases blood flow to the heart

10. cAMP and cGMP are derived from
Options
A. ATP and GTP by the actions of adenylate cyclase and guanylate cyclase respectively
B. GTP and ATP by the actions of adenylate cyclase and guanylate cyclase respectively
C. ATP and GTP by the actions of guanylate cyclase and adenylate cyclase respectively
D. none of the above

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