Mitosis and Chromosome Dynamics (2C) - Bio & Biochem

1. What is the key event of S phase that changes chromosome structure before mitosis?

   DNA replication producing sister chromatids. S phase duplicates the genome, forming paired chromatids essential for equal segregation during mitosis.

2. What structure forms the cleavage furrow during animal cell cytokinesis?

   Actin-myosin contractile ring. The ring constricts the plasma membrane, pinching the cell into two via actin-myosin contraction.

3. Identify the term for failure of sister chromatids to separate properly during mitosis.

   Nondisjunction. Nondisjunction leads to aneuploidy by causing unequal chromosome distribution to daughter cells.

4. What is the defining event of prophase in mitosis?

   Chromatin condenses into visible chromosomes. Condensation compacts DNA for efficient segregation, marking the start of mitotic chromosome visibility.

5. What is the primary purpose of mitosis in multicellular eukaryotes?

   Produce two genetically identical somatic daughter cells. Mitosis maintains genetic stability by duplicating and evenly distributing chromosomes to support growth and repair in somatic tissues.

6. What is the cell plate in plant cytokinesis?

   Vesicle-derived partition that becomes the new cell wall. The plate forms from Golgi vesicles, depositing materials to build a new wall between plant daughter cells.

7. Identify the DNA content change in a diploid cell from G$1$ to G$2$ using C notation.

   G$1$: $2C$ G$2$: $4C$. DNA replication in S phase doubles the genome from unreplicated diploid to replicated diploid content.

8. What is cohesin?

   Protein complex that holds sister chromatids together. Cohesin maintains chromatid pairing post-replication, ensuring accurate alignment until anaphase trigger.

9. What is the defining event of telophase?

   Nuclear envelopes reform and chromosomes decondense. Reformation restores nuclear integrity, while decondensation prepares chromosomes for interphase functions.

10. What is the defining event of anaphase?

    Sister chromatids separate and move to opposite poles. Separation allows replicated chromosomes to be pulled apart, ensuring each pole receives a complete set.

11. Which microtubules attach to kinetochores and move chromosomes?

    Kinetochore microtubules. Kinetochore microtubules capture and align chromosomes, generating force for poleward movement in anaphase.

12. What is the correct order of mitotic phases (excluding interphase)?

    Prophase prometaphase metaphase anaphase telophase. Mitotic phases progress from chromosome condensation to separation and nuclear reformation to ensure accurate genome distribution.

13. Which option best describes chromosome number per daughter cell after mitosis: $2n n 4n$?

    $2n$. Mitosis preserves the diploid chromosome number by equally dividing replicated chromosomes between daughters.

14. What enzyme cleaves cohesin to allow chromatid separation at anaphase?

    Separase. Separase proteolytically cleaves cohesin subunits, releasing chromatids for poleward migration in anaphase.

15. What is the defining event of metaphase?

    Chromosomes align at the metaphase plate. Alignment at the equator ensures balanced tension and equal chromosome distribution to daughter cells.

16. What is cytokinesis?

    Physical division of the cytoplasm into two daughter cells. Cytokinesis completes cell division by partitioning organelles and cytoplasm after nuclear separation.

17. What is the defining event of prometaphase?

    Nuclear envelope breaks down and kinetochores attach to spindle. Envelope breakdown allows spindle access to chromosomes, enabling microtubule-kinetochore interactions for alignment.

18. What is the spindle assembly checkpoint monitoring?

    Proper kinetochore attachment and tension before anaphase. The checkpoint prevents anaphase onset until all chromosomes are bipolarly attached, avoiding segregation errors.

19. What is a sister chromatid?

    One of two identical DNA copies joined at a centromere. Sister chromatids result from DNA replication, ensuring each daughter cell receives an identical genetic copy.

20. Which protein complex triggers anaphase by enabling sister chromatid separation?

    APC/C (anaphase-promoting complex/cyclosome). APC/C degrades securin, activating separase to initiate chromatid separation and anaphase progression.

21. What is the mitotic spindle primarily composed of?

    Microtubules and associated motor proteins. The spindle apparatus organizes and separates chromosomes through dynamic microtubule polymerization and motor protein activity.

22. Which microtubules anchor spindle poles to the cell cortex?

    Astral microtubules. Astral microtubules stabilize spindle orientation by interacting with cortical actin, ensuring symmetric division.

23. What is the kinetochore?

    Protein complex on centromere that binds spindle microtubules. Kinetochores facilitate chromosome movement by linking centromeres to microtubules during spindle assembly.

24. What is the centromere in a replicated chromosome?

    Region where sister chromatids are held together. The centromere provides the attachment site for spindle fibers and maintains chromatid cohesion until anaphase.

25. Which microtubules overlap at the midline and push spindle poles apart?

    Polar (interpolar) microtubules. Polar microtubules elongate the spindle by sliding past each other, facilitating cell elongation during anaphase.

Study these flashcards