Loading test…

AP Biology Unit 4: Cell Communication and Cell Cycle

12 questions

Header banner

Unit 4: Cell Communication and Cell Cycle

0 of 12 answered

~7 min left

Question 1

A signaling molecule binds a receptor on Cell A, triggering a phosphorylation cascade that activates a transcription factor. The transcription factor enters the nucleus and upregulates a gene encoding a secreted inhibitory protein. This protein then binds receptors on Cell A itself, reducing receptor activity. What type of signaling and feedback does this describe?

A.Paracrine signaling with positive feedbackB.Autocrine signaling with negative feedbackC.Endocrine signaling with negative feedbackD.Synaptic signaling with positive feedback

Question 2

A lipid-soluble steroid hormone passes through the plasma membrane and binds to an intracellular receptor. How does this differ from signaling through a membrane-bound receptor tyrosine kinase (RTK)?

A.Steroid hormones signal faster because they do not require a receptorB.Steroid signaling directly alters gene expression without a second messenger; RTK signaling uses a phosphorylation cascade in the cytoplasmC.RTK signaling requires the hormone to enter the nucleus, whereas steroid hormones act only at the plasma membraneD.Both pathways use cAMP as a second messenger to transmit their signals

Question 3

A researcher uses FRET (fluorescence resonance energy transfer) to show that a receptor dimerizes upon ligand binding. They then show that a truncated receptor that cannot dimerize fails to activate downstream targets even in the presence of ligand. Which of the following mechanisms is most directly disrupted by preventing dimerization?

A.Ligand binding, because dimerization is required for the receptor to adopt a ligand-binding conformationB.Receptor autophosphorylation and kinase activation, because transphosphorylation between dimerized subunits is required to activate the kinase domainC.Second messenger release, because dimerization directly synthesizes cAMPD.Receptor endocytosis, because dimerized receptors cannot be internalized

Question 4

During which phase of the cell cycle is DNA replicated?

A.G₁ phaseB.S phase (synthesis phase)C.G₂ phaseD.M phase (mitosis)

Question 5

Which of the following is an example of negative feedback in cell signaling?

A.Oxytocin release during labor stimulating more uterine contractions, which stimulate more oxytocin releaseB.High blood glucose stimulating insulin release, which lowers blood glucose, reducing insulin secretionC.A growth factor binding a receptor and triggering DNA replicationD.Calcium ions entering a muscle cell and triggering the release of more calcium

In-content ad

Question 6

Apoptosis (programmed cell death) is triggered in a cell with extensive DNA damage. Which of the following best describes why apoptosis is preferable to continued cell division in this scenario?

A.Apoptosis recycles all cellular components into new cells more efficiently than mitosisB.Continued division of damaged cells risks transmitting mutations to daughter cells, potentially creating tumor cellsC.DNA damage prevents the cell from completing S phase, so apoptosis allows other cells to divide in its placeD.Apoptosis sends chemical signals that directly reprogram neighboring cells to replicate the damaged cell's genome

Question 7

Epinephrine binds to a G protein-coupled receptor (GPCR) on a liver cell, leading to glycogen breakdown. Which of the following correctly describes the role of cAMP in this pathway?

A.cAMP acts as the first messenger that initially binds the receptorB.cAMP is a second messenger that activates protein kinase A, amplifying the signalC.cAMP directly breaks down glycogen by acting as a phosphorylase enzymeD.cAMP inhibits adenylyl cyclase to provide negative feedback immediately

Question 8

A researcher treats dividing cells with a drug that prevents the degradation of cyclin B. Based on your knowledge of the cell cycle checkpoint system, which of the following best predicts the result?

A.Cells arrest at the G₁/S checkpoint because cyclin B is needed for S phase entryB.Cells continuously enter and cannot exit mitosis, because MPF activity remains highC.Cells skip S phase because high MPF signals that DNA is already replicatedD.DNA replication occurs multiple times per cell cycle due to continuous cyclin B signaling

Question 9

Which of the following best describes a ligand in cell signaling?

A.A membrane protein that spans the lipid bilayer and detects signalsB.A signaling molecule that binds specifically to a receptorC.An intracellular enzyme that amplifies a signal cascadeD.A protein released at the synapse to change membrane potential

Question 10

During the spindle assembly checkpoint (SAC), the cell detects that one kinetochore is not attached to a spindle microtubule. Which of the following correctly describes what happens next?

A.The cell immediately undergoes apoptosis because improper attachment signals DNA damageB.The cell arrests in metaphase by inhibiting the APC/C until all kinetochores are properly attachedC.The cell advances to anaphase while attempting to correct the attachmentD.The unattached chromosome is degraded by proteosomes before cell division continues

In-content ad

Question 11

A mutation in a proto-oncogene converts it to an oncogene, causing the encoded growth factor receptor to be constitutively active (always 'on') regardless of whether a ligand is bound. Which of the following best explains why this promotes uncontrolled cell division?

A.The constitutively active receptor signals the cell to skip checkpoints by degrading p53B.The receptor continuously transmits growth and division signals even without a growth factor ligandC.The receptor migrates into the nucleus and directly activates cell cycle genesD.The receptor recruits additional copies of itself, increasing the number of functional receptors

Question 12

Loss-of-function mutations in both copies of the Rb (retinoblastoma) gene lead to uncontrolled cell division. Based on the role of Rb protein in the cell cycle, explain which checkpoint is affected and how.

A.The G₂/M checkpoint is affected; loss of Rb allows cells to enter mitosis with unreplicated DNAB.The G₁/S checkpoint is affected; loss of Rb constitutively releases E2F, driving unscheduled S phase entryC.The spindle assembly checkpoint is affected; Rb normally prevents kinetochore assemblyD.All checkpoints are simultaneously inactivated because Rb coordinates all CDK-cyclin pairs

AP Biology Unit 4: Cell Communication and Cell Cycle — Free with Answer Explanations | Test Practice Hub