Question

ap biology: signal transduction, mcq review (accuracy graded)

1. many human cells can be stimulated to divide by hormone - like growth factors that bind to receptor proteins (r) on the plasma membrane and trigger an internal signal - transduction cascade. in many cases, however, the process of contact inhibition prevents mitosis when cells are in direct contact with one another. contact inhibition occurs when proteins called cell adhesion molecules (cams) interact, causing them to change shape so that the growth - factor signaling proteins that normally associate with cams are replaced by another protein, called m. both pathways are depicted in the figures below. which of the following statements accurately uses the information presented to support the hypothesis that interruption of m function in a single body cell can result in cancer?

a. protein 3 will be prevented from interacting with cams, causing the cell cycle to stop permanently.
b. the ras protein will remain bound to dna, blocking expression of genes required for mitosis.
c. growth - factor signaling can trigger mitosis in cells that are in direct contact with other cells.
d. the receptor proteins of body cells will no longer bind to growth - factor proteins.
(there are two figures here, one for dividing cell and one for contact inhibition)
use the figure to the right & the following information to answer questions 2 - 3.
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.

1. which of the following outcomes will most likely result from the irreversible binding of gdp to the g protein?

a. the intracellular concentration of glycogen will increase.
b. the intracellular concentration of activated protein kinase a will increase.
c. the intracellular concentration of cyclic amp will increase.
d. the intracellular concentration of glucose - 1 - phosphate will increase.

1. 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 bins 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.

1. 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. loss - of - function mutations in ethylene receptors result in changes to the ripening process.
d. ethylene synthesis is under both positive and negative feedback regulation.
(there is a figure 1: a simplified model of the epinephrine signaling pathway in muscle cells)

Explanation:

Question 1

To solve this, we analyze each option:

• Option a: If M function is interrupted, contact inhibition fails, so cell cycle wouldn't stop. Eliminate a.
• Option b: Ras protein binds to GTP (not DNA) in signaling. Eliminate b.
• Option c: If M (which replaces growth - factor signaling proteins in contact inhibition) is interrupted, growth - factor signaling can trigger mitosis even in contact with other cells, leading to uncontrolled division (cancer). This makes sense.
• Option d: Receptor binding to growth factors isn't affected by M's function. Eliminate d.

The epinephrine signaling pathway: GDP - bound G - protein is inactive. If GDP binds irreversibly to G - protein:

• Option a: The pathway for glycogen breakdown to glucose - 1 - phosphate is inhibited. So glycogen (storage form) will accumulate, increasing its intracellular concentration.
• Option b: Activated protein kinase A won't increase as the pathway is inhibited. Eliminate b.
• Option c: Cyclic AMP won't increase as the pathway is inhibited. Eliminate c.
• Option d: Glucose - 1 - phosphate won't increase (pathway inhibited). Eliminate d.

A catabolic process breaks down molecules.

• Option a: Binding to transmembrane protein doesn't relate to catabolism. Eliminate a.
• Option b: G - protein subunits don't relate to catabolism. Eliminate b.
• Option c: Phosphorylase kinase catalyzing ATP hydrolysis is part of the pathway but not direct evidence of catabolism. Eliminate c.
• Option d: Glycogen phosphorylase converting glycogen (a polymer) to glucose - 1 - phosphate (a monomer) is a catabolic breakdown. This justifies the claim.

Answer:

c. Growth - factor signaling can trigger mitosis in cells that are in direct contact with other cells.

Question 2