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Questions and Answers
What is the primary role of motor proteins like dynein or kinesin during anaphase?
Which phase of mitosis is characterized as the shortest?
What happens to the spindle apparatus during telophase?
During which stage of mitosis are the nucleoli re-formed?
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What structure initiates cell plate formation in certain plants?
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How do sister chromatids behave during anaphase?
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What is the main component of the elastic 'cage' formed during mitosis around the spindle?
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How do daughter nuclei produced during mitosis compare to the original nucleus?
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What happens to chromatin during prophase?
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Why is the phase called 'mitosis'?
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What characterizes late prophase?
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What is the function of centromeres?
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What is a key event that marks the end of prophase?
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What describes the role of polar microtubules in metaphase?
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What occurs during metaphase?
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What are the two major classes of spindle microtubules?
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Study Notes
Prophase: Chromosome Shortening and Thickening
- Transition from G2 of interphase to prophase is gradual and lacks a clear border.
- Chromatin condenses into visible chromosomes, initially appearing as elongated threads.
- The term "mitosis" derives from the threadlike structure of chromosomes.
- Late prophase features distinct chromosomes made of two identical sister chromatids.
- Sister chromatids form during the S phase and are aligned nearly parallel, with centromeres constricted.
- Centromeres are crucial for binding chromosomes to the mitotic spindle during metaphase.
- Microtubules appear around the nuclear envelope and align as prophase progresses.
- The prophase spindle symbolizes the early assembly of the mitotic spindle.
- The nucleolus becomes indistinct and disappears as prophase concludes.
- The nuclear envelope breakdown marks the end of prophase.
Metaphase
- Metaphase starts with the formation of the mitotic spindle composed of spindle fibers (microtubules).
- Kinetochore microtubules attach to spindle and are specialized protein complexes facilitating chromosome movement.
- Polar microtubules stretch from pole to pole, connecting to sister chromatids at opposite ends.
- Kinetochores align chromosomes at the equatorial plane of the spindle during full metaphase.
- All chromosomes must align midway between spindle poles for proper separation of chromatids.
Mitotic Spindle Microtubules
- Spindle microtubules are categorized into kinetochore and polar microtubules.
- Spindle microtubules have one end near a pole, while the other end is directed away.
- Polar microtubules overlap with those from opposite poles, forming a balanced spindle structure.
- Actin filaments create an elastic "cage" around the spindle during mitosis.
Anaphase in Mitosis
- Anaphase is the shortest mitotic phase, focused on separating sister chromatids at centromeres.
- Sister chromatids, now termed daughter chromosomes, migrate towards opposite poles.
- Identical sets of chromosomes move quickly due to shortening of kinetochore microtubules.
- Motor proteins (dynein and kinesin) utilize ATP to transport chromosomes along microtubules, with tubulin subunits being lost.
Telophase in Mitosis
- Telophase marks the final stage of mitosis, leading to the formation of two nuclei around separated chromosome sets.
- The spindle apparatus dismantles, and chromosomes elongate into slender threads.
- Nucleoli reappear during telophase; daughter nuclei enter interphase.
- Daughter nuclei are genetically identical to each other and to the original nucleus.
- The nucleus contains essential instructions for protein synthesis, transferred to daughter cells.
- Duration of mitosis varies by tissue and organism; prophase is the longest, anaphase is the shortest.
Cell Plate Formation
- Following mitosis, cell division usually proceeds via membrane constriction and cell wall ingrowth.
- In bryophytes, vascular plants, and some algae, a cell plate forms during division.
- A phragmoplast, made of microtubules, develops between the daughter nuclei during early telophase.
- Phragmoplast contains actin filaments parallel to microtubules, which do not overlap.
- Cell plate initiation occurs as a disk suspended in the phragmoplast but does not reach cell walls during early formation.
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Description
Explore the key features of prophase in mitosis, focusing on the transition from G2 of interphase. This quiz covers chromosome shortening and thickening, the distinct appearance of sister chromatids, and the overall process involved in forming chromosomes.
