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.
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.