Question 1

Which of the following activities would lead to a decrease in the level of IP₃ in the cytosol? A)increased activity of inositol polyphosphate 5-phosphatase B)increased activity of phospholipase C C)increased activation of protein kinase C D)increased Ca²⁺concentration E)all of the above

Accepted Answer

Inositol polyphosphate 5-phosphatase is responsible for the breakdown of IP₃, therefore an increase in its activity would lead to a decrease in the level of IP₃ in the cytosol. Increased activity of phospholipase C, increased activation of protein kinase C, and increased Ca²⁺ concentration all result in the production of IP₃ or its precursor, therefore would not lead to a decrease in its level in the cytosol.

Question 2

Anthrax toxin functions by altering levels of cAMP.The toxin also contains an edema factor, which requires the activity of calmodulin (CaM)for proper function.Based on this information, which of the following can you conclude?
A)The toxin alters cAMP dependent cell signaling.
B)Calcium levels affect the function of the edema factor.
C)Unlike other toxins, the anthrax toxin does not function by altering biochemical signaling.
D)A and B
E)A and C

Accepted Answer

The information given indicates that the anthrax toxin alters levels of cAMP and contains an edema factor that requires the activity of calmodulin. Therefore, we can conclude that the toxin alters cAMP-dependent cell signaling (A) and that calcium levels affect the function of the edema factor (B). The information does not suggest that the toxin does not function by altering biochemical signaling (C), so this answer option is incorrect.

Question 3

Autoinhibition in the SH2 and SH3 domains
A)occurs when a SH2 phospho-Tyr forms a salt bridge with an Arg on SH3.
B)occurs when a SH2 phospho-Tyr binds a Pro segment on the SH3 domain, therefore blocking the active site and burying the required Tyr.
C)occurs when a salt bride forms between the active site phosphor-Tyr on SH3 and the Glu on the activation loop.
D)occurs when the salt bridge between Glu and Arg is broken.
E)None of the above is correct.

Accepted Answer

Autoinhibition in the SH2 and SH3 domains occurs when a SH2 phospho-Tyr binds a Pro segment on the SH3 domain, therefore blocking the active site and burying the required Tyr. This prevents the domain from interacting with other proteins until it is activated by a specific signal. The other options are incorrect.

Question 4

Scaffold proteins limit
A)oncogene transfer.
B)MAPK activity.
C)cross-talk.
D)cell differentiation.
E)signal amplification.

Accepted Answer

Scaffold proteins play a critical role in signal transduction by bringing together multiple signaling components for efficient pathway activation. However, scaffold proteins may also limit crosstalk between different signaling pathways, ensuring that signals are transmitted in a specific and controlled manner.

Question 5

Sildenafil (Viagra)
A)inhibits activity of a phosphoprotein phosphatase.
B)increases the relative concentration of cGMP.
C)increases the relative concentration of nitric oxide in the blood.
D)A, B, and C
E)A and B

Accepted Answer

Sildenafil (Viagra®) works by inhibiting phosphodiesterase type 5 (PDE5), an enzyme that breaks down cyclic guanosine monophosphate (cGMP), thereby increasing the relative concentration of cGMP. This leads to smooth muscle relaxation and increased blood flow to the penis, facilitating erection. It does not directly increase nitric oxide levels nor inhibit phosphoprotein phosphatase.

Question 6

Oncogenes
I.function as cell cycle inhibitors.
II.encode a protein which block cell cycle inhibition.
III.are expressed by cells that have higher levels of human growth hormone.
IV.can function as transcription factors.
A)I, III, IV
B)II, III
C)III, IV
D)II, IV
E)II

Accepted Answer

Oncogenes encode proteins that promote cell cycle progression by blocking cell cycle inhibition. They can also function as transcription factors. However, they are not expressed by cells with higher levels of human growth hormone. Therefore, options I and III are incorrect and option C is incomplete. Option II is partially correct, but oncogenes do not function as cell cycle inhibitors. Therefore, the best choice is D, which includes both correct statements about oncogenes.

Question 7

Which of the following best describe the mechanism of calmodulin (CaM)mediated activation? A)Ca²⁺ binding to calmodulin (CaM)results in conformational change that exposes a hydrophobic patch capable of binding to calcium sensitive protein kinase B)a conformational change induced by the binding of Ca²⁺ results in the release of the phosphate group in calmodulin (CaM) C)calmodulin (CaM)sensitive protein kinase dimerizes forming a joint active site capable of tightly binding Ca²⁺ D)phosphorylation of a tyrosine on calmodulin induced a conformational change that results in release of Ca²⁺ from the cytosol. E)none of the above.

Accepted Answer

The mechanism of calmodulin (CaM)-mediated activation involves Ca²⁺ binding to calmodulin (CaM), resulting in a conformational change that exposes a hydrophobic patch capable of binding to calcium-sensitive protein kinase. This binding ultimately leads to activation of the kinase. None of the other answer choices accurately describe this mechanism.

Question 8

Which of the following is always true of hormones?
A)Hormones always bind membrane bound receptors.
B)Hormones elicit specific cellular responses.
C)Hormones are secreted from a gland via a robust network of ducts.
D)The release of hormones is influenced by adrenal receptors.
E)All of the above are true.

Accepted Answer

Hormones are chemical messengers that are produced and secreted by endocrine glands. They travel via the bloodstream to target cells, where they bind to specific receptors and elicit a specific cellular response. While some hormones may bind to membrane-bound receptors, others may bind to intracellular receptors. Additionally, hormones may be secreted by a gland without the use of ducts (endocrine glands) or may be secreted by glands that use ducts (exocrine glands). The release of hormones can be influenced by a variety of factors, including feedback mechanisms and signaling pathways, but not by adrenal receptors specifically. Therefore, option B is the best choice as it accurately represents the general characteristics of hormones.

Question 9

Which of the following correctly states an essential step in the function of heterotrimeric G protein function?
A)A cascade of events must occur that ultimately activate protein kinase C.
B)Binding of a hormone to a receptor must signal the exchange of GDP for GTP.
C)Binding of GTP to the receptor protein must induce a change in conformation of the receptor.
D)Binding of cAMP to the α subunit of the G protein must initiate translocation of the subunit.
E)All of the above are correct.

Accepted Answer

The binding of a hormone to its receptor causes a conformational change in the receptor that allows it to catalyze the exchange of GDP for GTP in the alpha subunit of the G protein. This results in the activation of downstream signaling pathways. The other options listed describe various downstream events that occur as a result of G protein activation, but they are not essential steps in the function of the G protein itself.

Question 10

Which of the following describes the similarity between the following words? DAG, cAMP, IP3
A)All of them induce conformational changes in PKA.
B)All of them activate adenylate cyclase.
C)All of them require phosphorylation in order to function.
D)All of them function as second messengers.
E)All them result from the activity of phosphoprotein lipase.

Accepted Answer

DAG, cAMP, and IP3 are all examples of second messengers, which are intracellular signaling molecules that are generated in response to the binding of an extracellular ligand to a receptor. Second messengers then relay the signal to downstream effectors, such as enzymes or ion channels, ultimately leading to a cellular response. DAG, cAMP, and IP3 all function as second messengers in different signaling pathways.

Quiz 13: Biochemical Signaling

Which of the following activities would lead to a decrease in the level of IP₃ in the cytosol?

Anthrax toxin functions by altering levels of cAMP.The toxin also contains an edema factor, which requires the activity of calmodulin (CaM) for proper function.Based on this information, which of the following can you conclude?

Autoinhibition in the SH2 and SH3 domains

Scaffold proteins limit

Sildenafil (Viagra)

Oncogenes I.function as cell cycle inhibitors. II.encode a protein which block cell cycle inhibition. III.are expressed by cells that have higher levels of human growth hormone. IV.can function as transcription factors.

Which of the following best describe the mechanism of calmodulin (CaM) mediated activation?

Which of the following is always true of hormones?

Which of the following correctly states an essential step in the function of heterotrimeric G protein function?

Which of the following describes the similarity between the following words? DAG, cAMP, IP3