Cell Cycle - AP Biology

What is the main function of p53 in the cell cycle?

Halts cycle for DNA repair or triggers apoptosis. Guardian of genome responds to DNA damage signals.
Identify the structure that forms during plant cell cytokinesis to separate daughter cells.

Cell plate (from vesicles) that becomes new cell wall. Golgi vesicles fuse to create separating membrane wall.
Which checkpoint verifies DNA replication completion and damage repair before mitosis?

G $_2$ checkpoint. Ensures genome integrity before nuclear division begins.
Identify the term for uncontrolled cell division.

Cancer. Results from loss of cell cycle control mechanisms.
Identify the phase where crossing over occurs.

Prophase I of meiosis. Genetic recombination occurs between homologous chromosomes.
Identify the structure that forms the cleavage furrow in animal cell cytokinesis.

Actinmyosin contractile ring. Contractile proteins create constriction that divides cytoplasm.
What process follows telophase in the cell cycle?

Cytokinesis. The process that physically divides the cell into two.
What is a cell cycle checkpoint?

Control point where stop/go signals regulate cycle. Quality control mechanisms that monitor cell cycle progress.
What is the main purpose of the G₁ checkpoint?

Assess cell size, nutrients, DNA damage. Determines if the cell is ready for DNA replication.
What occurs during the S phase of the cell cycle?

DNA replication. The synthesis phase where chromosomes are duplicated.
What is the primary event that occurs in G₀ phase?

Cell cycle arrest. Non-dividing state where cells exit the active cycle.
What is G $_0$ phase?

Nondividing state outside the cell cycle. Quiescent cells exit cycle temporarily or permanently.
What are the phases of the cell cycle?

G₁, S, G₂, M. The sequential order of the four main cell cycle phases.
What is the primary event of S phase?

DNA replication (chromosomes are duplicated). Each chromosome is copied to form sister chromatids.
What is the primary function of mitosis?

Generate two identical daughter cells. Nuclear division producing genetically identical offspring.
What protein complex is activated by cyclins?

Cyclin-dependent kinases (CDKs). Enzymes that phosphorylate target proteins when bound to cyclins.
What is an oncogene?

Mutated gene that promotes uncontrolled cell division. Drives excessive proliferation when growth controls fail.
What is a tumor suppressor gene?

Gene that restrains division; loss increases cancer risk. Normally prevents cancer by controlling cell division.
Identify the phase where the spindle fibers attach to kinetochores.

Prometaphase. Nuclear envelope breaks down and spindle attaches.
What is the difference between mitosis and meiosis?

Mitosis produces identical cells; meiosis produces gametes. Mitosis maintains chromosome number; meiosis reduces it.
Which spindle microtubules push poles apart by overlapping at the cell center?

Nonkinetochore (polar) microtubules. Elongate spindle by sliding past each other.
Which option correctly states chromosome and chromatid counts at metaphase for a diploid cell with $2n=8$ ?

8 chromosomes and 16 chromatids. Condensed duplicated chromosomes align before chromatid separation.
What is the primary purpose of M phase?

Mitosis and cytokinesis to form two daughter cells. Nuclear division followed by cytoplasmic division.
What molecules directly drive cell-cycle transitions by phosphorylating target proteins?

Cyclin-dependent kinases (CDKs). Protein kinases that phosphorylate substrates when activated.
What key event defines anaphase?

Sister chromatids separate and move to opposite poles. Chromosome segregation ensures equal genetic distribution.
Identify the complex that promotes the G $_2$ M transition in many eukaryotic cells.

MPF (M-phase promoting factor: cyclin BCDK1). Key regulatory complex controlling entry into mitosis.
What key event defines prometaphase?

Nuclear envelope breaks down; spindle attaches to kinetochores. Spindle captures chromosomes after nuclear envelope fragments.
What is a key feature of the metaphase checkpoint?

Ensure chromosomes are aligned at metaphase plate. Prevents anaphase until all chromosomes are attached.
What is a kinetochore?

Protein structure on centromere where spindle attaches. Specialized protein complex linking chromosomes to spindle fibers.
What is the function of the p53 protein?

Regulates cell cycle and apoptosis. Tumor suppressor protein that monitors DNA damage.
What phase follows prophase in mitosis?

Metaphase. Chromosomes align at the cell center after condensing.
What is density-dependent inhibition?

Crowding stops division due to reduced growth signaling. Contact inhibition limits proliferation at high cell density.
What is the immediate effect of MPF activation on the cell?

Triggers mitosis, including nuclear envelope breakdown. Phosphorylates nuclear proteins to start chromosome condensation.
What is the primary purpose of G $_1$ phase?

Cell growth and normal metabolic activity. Cell increases size and synthesizes proteins for normal functions.
What structure forms during cytokinesis in plant cells?

Cell plate. Plant-specific structure that divides the cytoplasm.
What is the significance of telomeres in cell division?

Protect chromosome ends, limit cell division. Prevent chromosome degradation and count cell divisions.
Identify the checkpoint between G₁ and S phase.

G₁ checkpoint. The restriction point controlling entry into S phase.
What is a proto-oncogene?

Normal gene that can become an oncogene if mutated. Codes for growth-promoting proteins in normal cells.
Which checkpoint ensures all chromosomes are attached to the spindle before anaphase?

M checkpoint (spindle assembly checkpoint). Prevents premature chromatid separation during mitosis.
What is the role of the Rb protein in the cell cycle?

Inhibits cell cycle progression. Tumor suppressor that blocks $G_1$ to S transition.
What is the purpose of the cell cycle control system?

Regulate timing of cell cycle events. Checkpoints and molecular machinery coordinate cell division.
What is the role of cohesin in chromosome structure?

Holds sister chromatids together until anaphase. Protein ring maintaining chromosome cohesion during replication.
What is anchorage dependence in animal cells?

Cells must attach to a substrate to divide. Cell adhesion requirement for normal cell division.
What is the definition of cytokinesis?

Division of the cytoplasm to form two cells. Physical separation creating two distinct cells.
What does G₁ stand for in the cell cycle?

Gap 1 phase. The first gap phase between mitosis and DNA synthesis.
Identify the phase where chromosomes line up at the cell equator.

Metaphase. Chromosomes align at the metaphase plate before separation.
What structure is responsible for separating chromosomes during mitosis?

Mitotic spindle. The protein structure that pulls chromosomes apart.
What is the correct order of the eukaryotic cell cycle phases (including interphase and M phase)?

G $_1$ S G $_2$ M. Standard sequence: Gap1, Synthesis, Gap2, Mitosis phases.
What is the role of growth factors in the cell cycle?

Stimulate cell division. External signals that promote cell cycle progression.
What is the definition of mitosis?

Division of the nucleus into two genetically identical nuclei. Ensures equal genetic distribution to daughter cells.
Identify the final phase of mitosis.

Telophase. Nuclear envelopes reform and chromosomes begin to decondense.
What enzyme complex triggers sister chromatid separation at anaphase?

APC/C activates separase to cleave cohesin. Controls anaphase onset by removing chromatid cohesion.
Define cytokinesis.

Division of cytoplasm. The final step that creates two separate cells.
What key events define telophase?

Nuclei reform; chromosomes decondense; spindle disassembles. Mitosis concludes with nuclear reformation and chromosome relaxation.
Which phase of the cell cycle is the longest?

Interphase. Includes $G_1$ , S, and $G_2$ phases for cell growth.
What is the role of the spindle assembly checkpoint?

Ensure spindle fibers are properly attached. Prevents chromosome separation until proper attachment occurs.
What type of signaling typically promotes cell division by stimulating cyclinCDK activity?

Growth factors (external signals). Extracellular signals that promote cell cycle progression.
What does G₂ stand for in the cell cycle?

Gap 2 phase. The second gap phase between DNA synthesis and mitosis.
What is the role of cyclins in cell-cycle control?

They activate CDKs by binding; levels fluctuate. Regulatory proteins that rise and fall cyclically.
What is the correct order of mitotic stages?

Prophase Prometaphase Metaphase Anaphase Telophase. Sequential stages of nuclear division process.
What is the term for programmed cell death?

Apoptosis. Controlled cell death to eliminate damaged cells.
What is the name of the process that reduces chromosome number by half?

Meiosis. Reduction division producing haploid gametes from diploid cells.
Which spindle microtubules attach directly to kinetochores?

Kinetochore microtubules. Direct connection between spindle apparatus and chromosomes.
What occurs during anaphase of mitosis?

Sister chromatids separate. Spindle fibers pull sister chromatids to opposite poles.
In which phase do centrosomes move to opposite poles?

Prophase. Centrosomes organize spindle formation at opposite ends.
Which option correctly states chromosome and chromatid counts after S phase for a diploid cell with $2n=6$ ?

6 chromosomes and 12 chromatids. After replication, chromosome number stays same but chromatids double.
Which spindle microtubules anchor the spindle to the cell cortex?

Astral microtubules. Position and orient spindle within the cell.
What is the primary purpose of G $_2$ phase?

Growth and preparation for mitosis; error checking. Ensures cell is ready and DNA is intact before division.
What is the role of cyclins in the cell cycle?

Regulate cell cycle progression. Proteins that control timing of cell cycle transitions.
Which checkpoint decides whether a cell enters S phase from G $_1$ ?

G $_1$ checkpoint (restriction point). Also called restriction point; commitment to DNA synthesis.
What is the main function of the Rb (retinoblastoma) protein at the G $_1$ checkpoint?

Inhibits S-phase entry until phosphorylated. Tumor suppressor blocking S-phase until growth signals arrive.
Identify the phase where chromosomes condense.

Prophase. When chromatin condenses into visible chromosomes.
What is interphase in the cell cycle?

G $_1$ , S, and G $_2$ ; growth and DNA replication prep. Three phases between cell divisions preparing for next division.
What occurs during the M phase of the cell cycle?

Mitosis and cytokinesis. Nuclear division followed by cytoplasm division.
What is checked at the G₂ checkpoint?

DNA integrity, DNA replication completion. Ensures DNA is properly replicated before mitosis.
What is the role of the enzyme telomerase?

Extends telomeres in germ cells and cancer cells. Maintains telomere length in stem and cancer cells.
In which phase does cytokinesis begin?

Telophase. Cytoplasm division overlaps with the final mitotic phase.
Which enzyme is responsible for DNA replication?

DNA polymerase. The main enzyme that synthesizes new DNA strands.
What key feature defines metaphase?

Chromosomes align at the metaphase plate. Chromosomes line up at cell equator before separation.
What key events define prophase?

Chromosomes condense; spindle begins forming. DNA compacts and mitotic apparatus begins assembly.
In which phase do nuclear envelopes reform?

Telophase. Nuclear membranes reassemble around each set of chromosomes.

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