AP Biology : 4.2 Introduction to Signal Transduction - Exam Style questions with Answer- MCQ

AP PhysicsAP Calculus AP ChemistryAP Biology

Question

$G$ proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a $G$ protein, the $G$ protein is activated. The $G$ protein then activates an enzyme that produces a second messenger called $cAMP$ .

Which of the following describes a critical role of $cAMP$ during the transduction stage of a $G$ protein signal transduction pathway?

A. $cAMP$ carries the signal to the nucleus of the cell and results in new sequences of nucleotides being added to the cell’s $DNA$ .

B. $cAMP$ binds the extracellular signal molecule and carries it to the intracellular target specified by the signal.

C. $cAMP$ modifies a specific monomer so that it can be added to an elongating structural macromolecule.

D. $cAMP$ results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.

▶️Answer/Explanation

Ans: D
Typically, $cAMP$ immediately activates protein kinase $A$ , which phosphorylates various other proteins. Kinases are a type of enzyme that activates proteins by transferring a phosphate group from $ATP$ . Kinases are involved in many signaling pathways in a wide variety of organisms.

Question

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. $AMP$ -activated protein kinase $(AMPK)$ is a major cellular regulator of glucose metabolism. Metformin activates $AMPK$ in liver cells but cannot cross the plasma membrane. By blocking $AMPK$ with an inhibitor, researchers found that $AMPK$ activation is required for metformin to produce an inhibitory effect on glucose production by liver cells.

Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver?

A. It is a secondary messenger that amplifies a signal through a cascade reaction.

B. It is a ligand that activates the signal transduction pathway of the activation of $AMPK$ .

C. It is an allosteric regulator that binds to a crucial section of the $DNA$ that makes the enzymes needed for glucose uptake.

D. It is a competitive inhibitor that binds to glucose and prevents it from entering the cell.

▶️Answer/Explanation

Ans: B
Since metformin does not cross the membrane, it is likely a ligand that binds to a receptor on the surface of the plasma membrane, initiating the signal transduction pathway.

Question

Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?

A. Specific genes are activated.

B. A second messenger molecule is produced.

C. A ligand binds to a receptor.

D. Specific proteins are synthesized.

▶️Answer/Explanation

Ans: A
The chemical messenger (ligand) first binds to a receptor, which then changes shape to initiate the signaling pathway.

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

Based on Figure 1, which of the following statements best describes the epinephrine signaling pathway?

A. It involves the opening and closing of ion channels.

B. In involves enzymes activating other enzymes.

C. It involves changes in the expression of target genes.

D. It involves protons moving down a concentration gradient.

▶️Answer/Explanation

Ans: B
Based on Figure 1, the epinephrine signaling pathway involves enzymes activating other enzymes. For example, the pathway includes several protein kinases, enzymes that catalyze the transfer of a phosphate group from $ATP$ to a protein substrate. As represented in Figure 1, protein kinase A catalyzes the transfer of a phosphate group from $ATP$ to phosphorylase kinase, which results in the activation of phosphorylase kinase. The activated phosphorylase kinase activates glycogen phosphorylase in a similar manner.

Question

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

Which of the following statements best describes the role of adenylyl cyclase in the epinephrine signaling pathway?

A. It converts a polymer to its monomer subunits.

B. It moves substances across the plasma membrane.

C. It accelerates the production of a second messenger.

D. It transfers phosphate groups from $ATP$ to protein substrates.

▶️Answer/Explanation

Ans: C
When activated, adenylyl cyclase accelerates a reaction in which $ATP$ is converted to cyclic $AMP$ , which acts as a second messenger in the epinephrine signaling pathway.

AP Biology : 4.2 Introduction to Signal Transduction – Exam Style questions with Answer- MCQ

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