AP Biology Flashcards: Regulation Of Cell Cycle

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This deck focuses on Regulation Of Cell Cycle, giving you a quick way to review the definitions, rules, and examples that matter most for AP Biology.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which protein complex ensures proper chromosome separation?

Answer: Cohesin complex. Holds sister chromatids together until anaphase.

Flashcard 2: Which option best distinguishes cytokinesis from mitosis?

Answer: Cytokinesis divides cytoplasm; mitosis divides the nucleus. Two distinct processes that together complete cell division into daughter cells.

Flashcard 3: What event characterizes the anaphase of mitosis?

Answer: Separation of sister chromatids. Cohesin cleavage allows chromosome movement to poles.

Flashcard 4: What is the main characteristic of the S phase?

Answer: DNA replication occurs. Chromosome duplication creates sister chromatids.

Flashcard 5: What is the most direct cell-cycle effect of p53 activation after DNA damage?

Answer: It induces p21 to inhibit CDKs and arrest the cycle (often at $G_1$). p21 binds and inhibits CDK complexes needed for S-phase progression.

Flashcard 6: Name the phase where spindle fibers attach to kinetochores.

Answer: Prometaphase. Transition phase where kinetochore assembly occurs.

Flashcard 7: Identify the immediate consequence if the M checkpoint fails during mitosis.

Answer: Chromosome mis-segregation leading to aneuploid daughter cells. Unequal chromosome distribution creates cells with abnormal chromosome numbers.

Flashcard 8: Which enzyme is activated by cyclins to progress the cell cycle?

Answer: Cyclin-dependent kinases (CDKs). Phosphorylate target proteins when bound to cyclins.

Flashcard 9: What is the effect of the overexpression of cyclin E?

Answer: Accelerated entry into S phase. Excessive cyclin E bypasses normal checkpoint control.

Flashcard 10: Which protein is crucial for the G₁ checkpoint control?

Answer: p53 protein. Guardian of the genome; halts cycle for DNA repair.

Flashcard 11: Identify the phase of mitosis where nuclear envelope re-forms.

Answer: Telophase. Final mitotic phase reverses nuclear breakdown.

Flashcard 12: Identify the phase of the cell cycle where DNA replication occurs.

Answer: S phase. Synthesis phase duplicates chromosomes for division.

Flashcard 13: Name the process responsible for dividing the cytoplasm after mitosis.

Answer: Cytokinesis. Contractile ring pinches cell membrane in two.

Flashcard 14: Which option best predicts the effect of a nonfunctional APC/C on mitosis?

Answer: Failure to enter anaphase due to securin and cyclin persistence. Unable to degrade key proteins required for anaphase progression and mitotic exit.

Flashcard 15: Which option best describes how cyclin levels typically change during the cell cycle?

Answer: They rise and fall due to regulated synthesis and proteasomal degradation. Periodic destruction and synthesis creates oscillating levels that drive transitions.

Flashcard 16: What is density-dependent inhibition in animal cells?

Answer: Crowding reduces division via cell-cell contact and signaling. Contact inhibition prevents overgrowth when cell density becomes too high.

Flashcard 17: What is the main characteristic of the S phase?

Answer: DNA replication occurs. Chromosome duplication creates sister chromatids.

Flashcard 18: What is the primary signal for mitotic entry?

Answer: Activation of cyclin B/CDK1 complex. Active kinase triggers nuclear envelope breakdown.

Flashcard 19: What is the role of growth factors in animal cell-cycle control?

Answer: They provide external signals that stimulate passage through $G_1$. Signal adequate nutrients and conditions for cell division to proceed.

Flashcard 20: Identify the checkpoint that prevents premature mitosis initiation.

Answer: G₂/M checkpoint. Ensures cell is ready for nuclear division.

Flashcard 21: Which checkpoint primarily verifies cell size, nutrients, and DNA integrity before DNA synthesis?

Answer: The $G_1$ checkpoint (restriction point in animals). Prevents S-phase entry if growth conditions are inadequate or DNA is damaged.

Flashcard 22: Identify the cell-cycle stage where sister chromatids are produced but still joined by cohesin.

Answer: After S phase (during $G_2$ and early M). Sister chromatids remain attached until anaphase when cohesin is cleaved.

Flashcard 23: Which enzyme degrades cohesin to allow anaphase progression?

Answer: Separase. Protease cleaves cohesin rings holding chromatids.

Flashcard 24: Which checkpoint confirms all kinetochores are attached to spindle microtubules before anaphase?

Answer: The M checkpoint (spindle assembly checkpoint). Prevents chromosome mis-segregation by ensuring proper spindle attachment.

Flashcard 25: Name the protein complex that degrades cyclins to regulate the cell cycle.

Answer: Anaphase-promoting complex (APC). Ubiquitin ligase targets cyclins for destruction.

Flashcard 26: What is the normal function of the Rb (retinoblastoma) protein in $G_1$?

Answer: It inhibits E2F, preventing transcription of S-phase genes. Hypophosphorylated Rb sequesters E2F; phosphorylation releases E2F to activate S-genes.

Flashcard 27: What is anchorage dependence in animal cells?

Answer: Cells must attach to a surface (ECM) to progress through the cell cycle. Prevents division of cells that have lost proper tissue contact.

Flashcard 28: In which phase are sister chromatids aligned at the cell's equator?

Answer: Metaphase. Chromosomes align at metaphase plate before separation.

Flashcard 29: Which protein can trigger apoptosis if DNA damage is irreparable?

Answer: p53 protein. Activates apoptotic pathway when damage is severe.

Flashcard 30: What is ubiquitination, in the context of cell-cycle control?

Answer: Covalent tagging of proteins for degradation by the proteasome. Small protein tag that marks regulatory proteins for destruction by proteasome.

Flashcard 31: What is the role of cyclins in the cell cycle?

Answer: Regulate the progression of the cell cycle. Oscillating proteins that activate CDKs at checkpoints.

Flashcard 32: Which checkpoint confirms all kinetochores are attached to spindle microtubules before anaphase?

Answer: The M checkpoint (spindle assembly checkpoint). Prevents chromosome mis-segregation by ensuring proper spindle attachment.

Flashcard 33: Which term best describes cancer cells dividing without anchorage dependence?

Answer: Anchorage-independent growth. Cancer cells can divide without attachment to extracellular matrix or surfaces.

Flashcard 34: What does the term "checkpoint" mean in the context of the cell cycle?

Answer: A control point that can pause progression until conditions are correct. Ensures proper order and prevents errors by monitoring completion of previous events.

Flashcard 35: Name the phase where cells exit the cell cycle and stop dividing.

Answer: G₀ phase. Quiescent state for non-dividing differentiated cells.

Flashcard 36: Which checkpoint is most directly activated by unreplicated DNA in eukaryotic cells?

Answer: The $G_2$ checkpoint. Detects incomplete DNA synthesis and halts progression until replication finishes.

Flashcard 37: What is the primary role of cyclins in regulating CDK activity?

Answer: They bind CDKs and activate them at specific cell-cycle stages. Cyclins provide timing and specificity by accumulating at precise cell-cycle phases.

Flashcard 38: Which phase follows the completion of mitosis?

Answer: Cytokinesis. Physical division of cytoplasm creates two cells.

Flashcard 39: Which checkpoint is most directly activated by unreplicated DNA in eukaryotic cells?

Answer: The $G_2$ checkpoint. Detects incomplete DNA synthesis and halts progression until replication finishes.

Flashcard 40: Which molecule acts as a checkpoint inhibitor in the G₂/M transition?

Answer: Chk1 kinase. DNA damage checkpoint kinase prevents mitotic entry.

Flashcard 41: What is the primary signal for mitotic entry?

Answer: Activation of cyclin B/CDK1 complex. Active kinase triggers nuclear envelope breakdown.

Flashcard 42: Which phase of mitosis involves chromatin condensation?

Answer: Prophase. First phase organizes chromosomes for division.

Flashcard 43: What protein complex triggers anaphase by ubiquitinating securin and cyclins?

Answer: APC/C (anaphase-promoting complex/cyclosome). Ubiquitin ligase that targets securin and M-cyclins for proteasomal degradation.

Flashcard 44: Identify the immediate consequence if the M checkpoint fails during mitosis.

Answer: Chromosome mis-segregation leading to aneuploid daughter cells. Unequal chromosome distribution creates cells with abnormal chromosome numbers.

Flashcard 45: What is the function of the protein kinase Wee1?

Answer: Inhibits CDKs to regulate cell cycle entry. Phosphorylates CDK1 to keep it inactive until appropriate.

Flashcard 46: Which checkpoint primarily ensures DNA replication is complete and undamaged before mitosis?

Answer: The $G_2$ checkpoint. Prevents mitosis when DNA replication errors or damage are detected.

Flashcard 47: Identify the phase in which the cell prepares for mitosis after DNA replication.

Answer: $G_2$ phase. Cell synthesizes proteins required for chromosome condensation and spindle formation.

Flashcard 48: Identify the phase where the cell grows and prepares for DNA replication.

Answer: G₁ phase. Gap phase for organelle synthesis and growth.

Flashcard 49: What molecular event inactivates Rb and promotes entry into S phase?

Answer: Phosphorylation of Rb by cyclin-CDK complexes. Phosphorylated Rb releases E2F transcription factor to promote S-phase entry.

Flashcard 50: What is the primary function of cyclin-dependent kinases (CDKs) in cell-cycle regulation?

Answer: They phosphorylate target proteins to drive cell-cycle transitions. Phosphorylation activates substrates that control key transitions like S-phase entry or mitosis onset.

Flashcard 51: Identify the mechanism that makes cyclin-CDK control largely unidirectional.

Answer: Irreversible proteolysis of key regulators (for example, cyclins) via APC/C. Once cyclins are destroyed, the process cannot reverse until new synthesis occurs.

Flashcard 52: What is the restriction point in animal cells, and where is it located in the cell cycle?

Answer: A commitment point in late $G_1$ after which the cell proceeds to S phase. Once passed, cells are committed to completing the division cycle.

Flashcard 53: Which protein regulates the G₂/M transition by inhibiting CDK1?

Answer: Wee1 kinase. Checkpoint kinase maintains $G_2$ arrest when needed.

Flashcard 54: What ensures the fidelity of chromosome segregation during mitosis?

Answer: Spindle assembly checkpoint. Monitors attachment status before allowing progression.

Flashcard 55: What is density-dependent inhibition in animal cells?

Answer: Crowding reduces division via cell-cell contact and signaling. Contact inhibition prevents overgrowth when cell density becomes too high.

Flashcard 56: What is the name of the nondividing state that cells can enter from $G_1$?

Answer: $G_0$ phase. Quiescent state where cells exit the cycle but remain metabolically active.

Flashcard 57: What is the role of the Rb protein in the cell cycle?

Answer: Inhibits the cell cycle; tumor suppressor. Retinoblastoma protein blocks $G_1$/S transition.

Flashcard 58: Which phase follows the completion of mitosis?

Answer: Cytokinesis. Physical division of cytoplasm creates two cells.

Flashcard 59: Identify the checkpoint ensuring all chromosomes are attached before anaphase.

Answer: Spindle assembly checkpoint. M checkpoint ensures proper chromosome attachment.

Flashcard 60: Which molecule is a key regulator of the G₁/S transition?

Answer: Cyclin D. Early cyclin promotes entry into S phase.

Flashcard 61: Which option best predicts the effect of a nonfunctional APC/C on mitosis?

Answer: Failure to enter anaphase due to securin and cyclin persistence. Unable to degrade key proteins required for anaphase progression and mitotic exit.

Flashcard 62: Which protein can trigger apoptosis if DNA damage is irreparable?

Answer: p53 protein. Activates apoptotic pathway when damage is severe.

Flashcard 63: Which option best predicts the effect of constitutively active cyclin-CDK complexes?

Answer: Premature checkpoint bypass and increased uncontrolled proliferation. Removes normal cell-cycle brakes, leading to continuous proliferation signals.

Flashcard 64: Name the phase where cells exit the cell cycle and stop dividing.

Answer: G₀ phase. Quiescent state for non-dividing differentiated cells.

Flashcard 65: What is the function of the proteasome in cell-cycle regulation?

Answer: It degrades ubiquitin-tagged regulatory proteins (for example, cyclins). Destroys cell-cycle regulators to ensure unidirectional progression through phases.

Flashcard 66: What is the consequence of a defective spindle assembly checkpoint?

Answer: Aneuploidy due to improper chromosome segregation. Unequal chromosome distribution causes genomic instability.

Flashcard 67: Which checkpoint primarily ensures DNA replication is complete and undamaged before mitosis?

Answer: The $G_2$ checkpoint. Prevents mitosis when DNA replication errors or damage are detected.

Flashcard 68: Identify the phase of mitosis where nuclear envelope re-forms.

Answer: Telophase. Final mitotic phase reverses nuclear breakdown.

Flashcard 69: Identify the phase where the cell grows and prepares for DNA replication.

Answer: G₁ phase. Gap phase for organelle synthesis and growth.

Flashcard 70: Identify the phase in which the cell primarily grows and performs normal functions before S phase.

Answer: $G_1$ phase. Cell accumulates materials and energy needed for DNA replication and division.

Flashcard 71: What is the role of p21 in regulating the cell cycle?

Answer: It is a CDK inhibitor that blocks cyclin-CDK activity. Blocks S-phase gene transcription by preventing E2F transcription factor activity.

Flashcard 72: Which protein regulates the G₂/M transition by inhibiting CDK1?

Answer: Wee1 kinase. Checkpoint kinase maintains $G_2$ arrest when needed.

Flashcard 73: Name the checkpoint that ensures DNA is undamaged before mitosis.

Answer: G₂/M checkpoint. Prevents mitosis with damaged or unreplicated DNA.

Flashcard 74: What role does the protein p21 play in the cell cycle?

Answer: Inhibits CDKs, acting as a checkpoint regulator. CDK inhibitor enforces $G_1$/S checkpoint arrest.

Flashcard 75: What is apoptosis, and how does it relate to cell-cycle regulation?

Answer: Programmed cell death that removes damaged or abnormal cells. Eliminates cells with irreparable damage that could bypass cell-cycle controls.

Flashcard 76: What ensures the fidelity of chromosome segregation during mitosis?

Answer: Spindle assembly checkpoint. Monitors attachment status before allowing progression.

Flashcard 77: What is a tumor suppressor gene?

Answer: A gene whose loss of function removes restraints on cell division. Normally acts as brake on cell division; loss promotes cancer development.

Flashcard 78: Which enzyme is activated by cyclins to progress the cell cycle?

Answer: Cyclin-dependent kinases (CDKs). Phosphorylate target proteins when bound to cyclins.

Flashcard 79: Which option best predicts the effect of a mutation preventing Rb phosphorylation?

Answer: Cell-cycle arrest in $G_1$ due to continued inhibition of E2F. Rb remains active and blocks E2F, preventing S-phase gene expression.

Flashcard 80: What does the term "checkpoint" mean in the context of the cell cycle?

Answer: A control point that can pause progression until conditions are correct. Ensures proper order and prevents errors by monitoring completion of previous events.

Flashcard 81: Identify the cell-cycle stage where sister chromatids are produced but still joined by cohesin.

Answer: After S phase (during $G_2$ and early M). Sister chromatids remain attached until anaphase when cohesin is cleaved.

Flashcard 82: What is the outcome of the G₁/S checkpoint activation?

Answer: Cell cycle arrest until DNA repair is complete. Halts progression until repair mechanisms finish.

Flashcard 83: Which enzyme degrades cohesin to allow anaphase progression?

Answer: Separase. Protease cleaves cohesin rings holding chromatids.

Flashcard 84: Identify the checkpoint ensuring all chromosomes are attached before anaphase.

Answer: Spindle assembly checkpoint. M checkpoint ensures proper chromosome attachment.

Flashcard 85: What is the effect of the overexpression of cyclin E?

Answer: Accelerated entry into S phase. Excessive cyclin E bypasses normal checkpoint control.

Flashcard 86: Which term best describes cancer cells ignoring density-dependent inhibition?

Answer: Loss of contact inhibition (reduced density-dependent inhibition). Cancer cells continue dividing despite crowded conditions that stop normal cells.

Flashcard 87: What is the primary function of cyclin-dependent kinases (CDKs) in cell-cycle regulation?

Answer: They phosphorylate target proteins to drive cell-cycle transitions. Phosphorylation activates substrates that control key transitions like S-phase entry or mitosis onset.

Flashcard 88: Identify the phase in which the cell primarily grows and performs normal functions before S phase.

Answer: $G_1$ phase. Cell accumulates materials and energy needed for DNA replication and division.

Flashcard 89: At which checkpoint is the cell cycle arrested if DNA damage is detected?

Answer: G₁/S checkpoint. Restriction point prevents replication of damaged DNA.

Flashcard 90: Which term best describes cancer cells ignoring density-dependent inhibition?

Answer: Loss of contact inhibition (reduced density-dependent inhibition). Cancer cells continue dividing despite crowded conditions that stop normal cells.

Flashcard 91: What event marks the beginning of prometaphase?

Answer: Nuclear envelope breakdown. Nuclear membrane dissolves for spindle access.

Flashcard 92: What is anchorage dependence in animal cells?

Answer: Cells must attach to a surface (ECM) to progress through the cell cycle. Prevents division of cells that have lost proper tissue contact.

Flashcard 93: What is the role of cyclins in the cell cycle?

Answer: Regulate the progression of the cell cycle. Oscillating proteins that activate CDKs at checkpoints.

Flashcard 94: Which molecule is a key regulator of the G₁/S transition?

Answer: Cyclin D. Early cyclin promotes entry into S phase.

Flashcard 95: What is a proto-oncogene?

Answer: A normal gene that can become an oncogene when mutated or overexpressed. Encodes proteins that normally promote controlled cell division and growth.

Flashcard 96: What is the restriction point in animal cells, and where is it located in the cell cycle?

Answer: A commitment point in late $G_1$ after which the cell proceeds to S phase. Once passed, cells are committed to completing the division cycle.

Flashcard 97: What is the name of the nondividing state that cells can enter from $G_1$?

Answer: $G_0$ phase. Quiescent state where cells exit the cycle but remain metabolically active.

Flashcard 98: What is the role of growth factors in animal cell-cycle control?

Answer: They provide external signals that stimulate passage through $G_1$. Signal adequate nutrients and conditions for cell division to proceed.

Flashcard 99: What is the primary function of the cell cycle?

Answer: To ensure accurate DNA replication and cell division. Prevents genetic defects by controlling division timing.

Flashcard 100: Which tumor suppressor protein can halt the cell cycle when DNA is damaged?

Answer: p53. Guardian of the genome that responds to DNA damage by activating checkpoints.