Question

6. Lipid-soluble signaling molecules, such as testosterone, cross the plasma membranes of all cells A) by diffusion but affect only target cells because only target cells retain the appropriate DNA segments. B) by diffusion but affect only target cells because only target cells have the intracellular receptors for testosterone. C) through hydrophilic channels of transmembrane proteins but affect only target cells because only target cells retain the appropriate DNA segments. D) through hydrophilic channels of transmembrane proteins but affect only target cells because only target cells have the intracellular receptors for testosterone. E) through hydrophilic channels of transmembrane proteins but affect only target cells because only target cells retain the appropriate DNA sequences and the intracellular receptors for testosterone. 7. The general name for an enzyme that transfers phosphate groups from ATP to a protein and is frequently used in transduction pathways is a A) protein kinase B) peptidase C) protein cyclase D) protein dehydrogenase 8. In general, during signal transduction pathways that include phosphorylation cascades: A) each protease activates the next due to conformational changes produced through phosphorylation and then protein phosphatases inactivate the previously activated protease in the cascade, turning off the signal transduction. B) ATP is generated by the phosphorylation cascade and then protein phosphatases inactivate the previously activated protease in the cascade, turning off the signal transduction C) protein phosphatases activate protein kinases, turning on signal transduction D) ATP is not involved and protein phosphatases turn on signal transduction by phosphorylating the next enzyme 9. Second messengers tend to be water-soluble and small so they can rapidly move throughout the cell by A) active transport; CAMP is a second messenger which is produced by the action of adenylvl eyelase, whereas Cail is stored in the cytoplasm ready to act as a second messenger. B) active transport; DAG is a second messenger which is produced by the action of adenylyl cyclase, whereas Car is stored in the cytoplasm ready to act as a second messenger. C) diffusion; CAMP is a second messenger which is produced by the action of adenylyl cyclase, whereas Cais stored at higher concentration in the Endoplasmic Reticulum ready to act as a second messenger Di diffusion: DAG is a second messenger which is produced by the action of adenylyl eyelase, whereas Cai stored at higher concentration in the cytoplasm ready to act as a second messenger

Answer 1

Question 6.)

Answer: B- by diffusion but affect only target molecules because only target molecules have the intracellular receptors for testosterone.

Explanation: As plasma membrane is made up of lipid bilayer only lipid soluble molecules are easily pass though the layer via simple diffusion. Target cells have the intracellular receptors which in not present on nontarget molecules. These intracellular receptors when activated by the signal molecule allows their interaction with the genes in the target cell nucleus.

Wrong answers:

Lipid soluble signal molecule are hydrophobic in nature hence the options C, D and E become incorrect because they won't need hydrophilic channels to cross. Moreover, retaining of DNA has no connection with intracellular receptors as lipid soluble signal molecule cannot directly direct the DNA. So intracellular receptors would be used as a marker and not relevant DNA. Hence, option A becomes incorrect.

Question 7:

Answer: A- Protein Kinase

Explanation: Kinases are the ones that transfers phosphate groups from ATP to a protein through process of phosphorylation and is frequently used in transduction pathways, metabolism, cell signalling and various other pathways.

Wrong Answers:

Option B: Peptidase are the ones which helps in the breakdown of peptides into amino acids. Hence, it is incorrect.

Option C: Cyclase converts ATP that helps in transferring signals. Hence, the option is incorrect.

Option D: Protein Dehydrogenase helps in the catalysis of pyruvate. Hence it is out of the box option and incorrect as well.

Question 8:

Answer: A- Each protease activates the next due to conformational changes produced through phosphorylation and then protein phosphatases activates the previously activated protease in the cascade turning off signal transduction.

Explanation: During signal trasduction, the work of phosphatase work is to turn off the signal transduction mechanism by removing phosphates from the enzyme. And confirmational changes in each protease due to protein kinase allows it to trigger next protease thus creating a phosphorylation cascade.

Wrong answers:

Protein phosphatases turns off the signal transduction by removing phosphates groups from the enzyme like kinase. Hence it rules out the Option D

Protein phosphatases reverses the effect of kinase and not activates it which makes the Option C incorrect.

ATP is hydrolysed and its phosphate is utilized and not generated by protein kinase in order to start the signalling mechanism which makes Option B incorrect. Moreover, phosphatase release the phoshate ions from pritein kinase, but does not generate ATP again from it as it would require energy.

Question 9:

Answer: C- diffusion; cAMP is a second messenger which is produced by the action of adenylyl cyclase, whereas CA2+ is stored at higher concentration in the Endoplasmic Reticulum ready to act as a second messenger.

Explanation: As second messengers are small and water soluble, they move through the process of diffusion and not by active transport (movement of molecules from lower concentrated region to higher concentrated region).

Wrong Answers:

Due to the above-mentioned explanation, Option A and B are ruled out.

Moreover, Calcium ions concentration in the cytosol is very low. This is due to the fact that the ion pumps in the lipid bilayer membrane work to remove it. Hence, they are stored in compartments such as the endoplasmic reticulum. Also, cCAMP is produced by cyclase while DAG is produced by phospholipase C. Hence this rule out the Option D.