AP Biology : 4.3 Signal Transduction – Exam Style questions with Answer- MCQ

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Question

During a fight-or-flight response, epinephrine is released into the body’s circulatory system and transported throughout the body. Some cells exhibit a response to the epinephrine while other cells do not.

Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?

A. Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding.

B. Cell signaling depends on the transduction of a received signal by the nervous system. Not all cells are close enough to a synapse to receive the signal and respond.

C. Cell signaling depends on the signal being able to diffuse through the cell membrane. Epinephrine is incapable of diffusing through some plasma membranes because of the membrane’s phospholipid composition.

D. Cell signaling requires reception, transduction, and response. All cells can receive epinephrine, all cells respond with a pathway, but only select cells have the proper coding in their DNA to respond.

▶️Answer/Explanation

Ans: A
Cell signaling starts with the reception of the signal. Not all cells are equipped to receive all signals. Only those cells with the correct receptor to a signal will be able to respond to a signal such as epinephrine.

Question

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome.

Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype?

A. If the SRY gene is absent or nonfunctional, the embryo will exhibit male sexual development.

B. If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.

C. An embryo with a male sex chromosome will always exhibit male sexual development.

D. An embryo with two male sex chromosomes will always exhibit male sexual development.

▶️Answer/Explanation

Ans: B
The SRY gene must be present and functional for normal male sexual development. It is the proper functioning of the SRY gene that is important, and this is the best statement to support the claim.

Question

Researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced−9 and ced−3 . The ced−3 gene was found to promote cell death, and ced−9 to inhibit it. The ced−9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis.

Which of the following statements best justifies the claim that changes in the expression of ced−9 in C. elegans can affect regulation of apoptosis in the cell?

A. An experiment showed that a mutation in the ced−9 gene led to excessive cell death in C. elegans.

B. An experiment showed that the ced−9 gene normally produces a protein that promotes excessive cell death in C. elegans.

C. A mutation in ced−3 will cause ced−9 to be incorrectly transcribed.

D. Apoptosis is dependent on a signal from the ced−9 gene in C. elegans.

▶️Answer/Explanation

Ans: A
If ced−9 acts as a regulator and normally inhibits apoptosis, then if it loses function, more cell death will occur.

Question

The epinephrine signaling pathway plays a role in regulating glucose homeostasis in muscle cells. The signaling pathway is activated by the binding of epinephrine to the beta-2 adrenergic receptor. A simplified model of the epinephrine signaling pathway is represented in Figure 1.

The figure presents a simplified model of the epinephrine signaling pathway in muscle cells. A plasma membrane is shown with two transmembrane structures, a Beta-2 Adrenergic Receptor and Adenylyl Cyclase. Epinephrine is shown binding to the extracellular surface of the beta-2 adrenergic receptor. Bound to the cytosolic surface of the receptor is a G protein made up of alpha, beta, and gamma subunits. An arrow indicates that G D P that is bound to the alpha subunit of the G protein is now released from the subunit. A successive arrow points to the G protein subunits dissociated from the adrenergic receptor and the alpha subunit dissociated from a complex of the beta and gamma subunits. G T P is shown binding to the alpha subunit. A successive arrow points from the G T P-modified alpha subunit to the cytosolic region of adenylyl cyclase. Adenylyl cyclase intersects an arrow that points from A T P to Cyclic A M P. A series of arrows follows. An arrow from Cyclic A M P points to Protein Kinase A. An arrow from Protein Kinase A points to Phosphorylase Kinase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Phosphorylase Kinase points to Glycogen Phosphorylase and is paired with a curved arrow pointing from A T P to A D P. An arrow from Glycogen Phosphorylase points to an arrow indicating the conversion of Glycogen to Glucose-1-Phosphate. A final arrow points from Glucose-1-Phosphate to Glycolysis.

Figure 1. A simplified model of the epinephrine signaling pathway in muscle cells

A researcher claims that the epinephrine signaling pathway controls a catabolic process in muscle cells. Which of the following statements best helps justify the researcher’s claim?

A. Epinephrine is a signaling molecule that binds to a transmembrane protein.

B. The G protein in the epinephrine signaling pathway consists of three different subunits.

C. Phosphorylase kinase catalyzes the hydrolysis of ATP.

D. Glycogen phosphorylase catalyzes the conversion of glycogen to glucose-1-phosphate.

▶️Answer/Explanation

Ans: D
Glycogen phosphorylase catalyzes the breakdown of glycogen, which is a catabolic process. Consequently, the statement helps justify the researcher’s claim.

Question

Ethylene causes fruits to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening.
Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?

A. Ethylene is a simple gaseous molecule, which makes it easily detected by receptors.

B. Fruit will ripen in closed containers without exposure to air.

C. Ethylene synthesis is under both positive and negative feedback regulation.

D. Loss-of-function mutations in ethylene receptors result in changes to the ripening process.

▶️Answer/Explanation

Ans: D
If ethylene is not perceived by the receptors, then ripening will not occur. This best justifies the claim that ethylene initiates the signal transduction pathway.

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