MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 2c Cell Cycle Regulation

What this deck covers

This deck focuses on 2c Cell Cycle Regulation, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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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: What is the primary function of p$53$ in cell-cycle regulation after DNA damage?

Answer: Induces cell-cycle arrest or apoptosis via transcriptional control. p$53$ activates genes for cycle arrest or apoptosis to eliminate damaged cells and maintain genomic stability.

Flashcard 2: What is the immediate role of separase during the metaphase-to-anaphase transition?

Answer: Cleaves cohesin to separate sister chromatids. Separase activation cleaves cohesin rings, enabling sister chromatid separation during anaphase.

Flashcard 3: What is the primary purpose of S phase in the cell cycle?

Answer: DNA replication (genome duplication). S phase duplicates the genome to provide identical DNA copies for distribution to daughter cells during division.

Flashcard 4: What is the immediate effect of retinoblastoma protein (Rb) when it is hypophosphorylated?

Answer: It inhibits E$2$F and blocks entry into S phase. Hypophosphorylated Rb represses E$2$F to prevent transcription of genes needed for S phase entry.

Flashcard 5: Which checkpoint primarily verifies completion of DNA replication and DNA integrity before mitosis?

Answer: G$2$/M checkpoint. The G$2$/M checkpoint confirms complete and accurate DNA replication to avoid errors in chromosome segregation.

Flashcard 6: What is the function of ATM/ATR kinases in response to DNA damage or replication stress?

Answer: Activate checkpoint signaling (for example, via Chk$1$/Chk$2$). ATM/ATR detect damage and phosphorylate effectors like Chk$1$/Chk$2$ to activate checkpoints and arrest the cycle.

Flashcard 7: What is the primary purpose of G$1$ phase in the cell cycle?

Answer: Cell growth and preparation for DNA synthesis. G$1$ phase enables cellular growth and synthesis of proteins and organelles necessary before committing to DNA replication.

Flashcard 8: How do cyclin levels typically change across the cell cycle compared with CDK levels?

Answer: Cyclins oscillate; CDK protein levels are relatively constant. Cyclin levels fluctuate to temporally control CDK activity, while CDKs remain stable throughout the cycle.

Flashcard 9: What is the effect of Rb phosphorylation by G$1$ cyclin-CDK complexes?

Answer: Rb releases E$2$F, promoting transcription of S-phase genes. Phosphorylation inactivates Rb, allowing E$2$F to drive expression of DNA synthesis genes.

Flashcard 10: What is the core biochemical function of cyclin-dependent kinases (CDKs)?

Answer: Serine/threonine kinases that phosphorylate cell-cycle targets. CDKs phosphorylate substrates to regulate transitions between cell cycle phases.

Flashcard 11: Which checkpoint ensures all chromosomes are properly attached to the spindle before anaphase?

Answer: Spindle assembly checkpoint (metaphase checkpoint). The spindle assembly checkpoint halts mitosis until all chromosomes achieve bipolar spindle attachment for equal segregation.

Flashcard 12: What is the role of E$2$F transcription factors in the cell cycle?

Answer: Activate transcription of genes required for S phase. E$2$F factors transcribe genes essential for DNA replication and S phase progression.

Flashcard 13: What is the defining chromosomal event of S phase that changes DNA content but not chromosome number?

Answer: Sister chromatid formation (DNA content doubles). DNA replication in S phase forms sister chromatids, doubling DNA without altering chromosome count.

Flashcard 14: Which two key substrates are ubiquitinated to allow anaphase onset and mitotic exit?

Answer: Securin and cyclin B. Ubiquitination of securin activates separase, while cyclin B degradation inactivates CDK$1$ for mitotic exit.

Flashcard 15: Identify the cell-cycle phase when chromosomes are most condensed and best visualized on a karyotype.

Answer: Metaphase of mitosis. Chromosomes condense maximally in metaphase to facilitate alignment and visualization on the mitotic spindle.

Flashcard 16: Which checkpoint is called the restriction point, and what decision does it control?

Answer: G$1$/S checkpoint; commit to division or enter G$0$. The restriction point at G$1$/S evaluates signals to decide on cell division commitment or quiescence.

Flashcard 17: What is G$0$ phase, and when do cells typically enter it?

Answer: Quiescent nondividing state entered from G$1$. G$0$ represents a resting state where cells exit the cycle from G$1$ to perform specialized functions without dividing.

Flashcard 18: What is the role of the anaphase-promoting complex/cyclosome (APC/C) in M phase?

Answer: E$3$ ubiquitin ligase that triggers anaphase and mitotic exit. APC/C ubiquitinates targets to promote their degradation, enabling anaphase and mitotic progression.

Flashcard 19: Identify the direct consequence of loss-of-function in p$53$ for cell-cycle control.

Answer: Failure of DNA-damage arrest; increased survival of damaged cells. p$53$ loss impairs damage response, allowing proliferation of mutated cells and promoting tumorigenesis.

Flashcard 20: Which CDK inhibitor is transcriptionally upregulated by p$53$ to enforce G$1$/S arrest?

Answer: p$21$. p$53$ induces p$21$ to inhibit CDKs, halting progression at G$1$/S in response to damage.

Flashcard 21: What must bind to a CDK to activate it for cell-cycle progression?

Answer: A cyclin. Cyclin binding confers activity and specificity to CDKs for phase-specific phosphorylation events.

Flashcard 22: What are the four main phases of the eukaryotic cell cycle in order?

Answer: G$1$  S  G$2$  M. The eukaryotic cell cycle progresses sequentially through these phases to coordinate growth, DNA replication, and division, ensuring genetic fidelity.

Flashcard 23: Which option best describes how growth factors promote G$1$ to S progression?

Answer: Increase cyclin expression to activate CDKs and phosphorylate Rb. Growth factors upregulate cyclins via signaling pathways, activating CDKs to phosphorylate Rb and release E$2$F for S phase genes.

Flashcard 24: What is the primary purpose of G$2$ phase in the cell cycle?

Answer: Growth and preparation for mitosis; DNA damage check. G$2$ phase allows further cellular growth and checks for DNA replication errors to prevent mitotic defects.

Flashcard 25: What is the primary purpose of M phase in the cell cycle?

Answer: Mitosis and cytokinesis to form two daughter cells. M phase divides the nucleus and cytoplasm to produce genetically identical daughter cells.