What is the fundamental definition of mitosis in the context of the eukaryotic cell cycle?

Mitosis is a crucial part of the cell cycle in eukaryotic cells where replicated chromosomes are precisely separated into two new nuclei. This process ensures that each resulting daughter cell is genetically identical to the parent cell, maintaining genetic stability across cell generations.

What biological process precedes mitosis, and what key event occurs during it?

Mitosis is preceded by the S phase of interphase. During the S phase, the cell replicates its DNA, ensuring that each chromosome consists of two identical sister chromatids before the cell division process begins.

What follows mitosis to complete the division of a cell, and what components are divided?

Following mitosis, telophase and cytokinesis occur. Cytokinesis is the process that divides the cytoplasm, organelles, and cell membrane of the parent cell into two distinct daughter cells, each containing one of the newly formed nuclei.

What is the primary outcome of mitosis and cytokinesis regarding the genetic material and cell number?

The primary outcome of mitosis and cytokinesis is the creation of two daughter cells that are genetically identical to the parent cell. This process effectively doubles the number of cells while maintaining the same genetic information in each new cell.

What are the distinct stages that comprise the mitotic phase (M phase) of the cell cycle?

The mitotic phase (M phase) of the cell cycle includes several distinct stages: preprophase (in plant cells), prophase, prometaphase, metaphase, anaphase, and telophase. These stages collectively describe the process of nuclear division.

How does DNA replication during interphase contribute to the process of mitosis?

During interphase, specifically the S phase, the cell duplicates its DNA. This replication results in each chromosome consisting of two identical sister chromatids, which are essential for the accurate separation and distribution to daughter cells during mitosis.

What are sister chromatids, and what structure holds them together before they separate during mitosis?

Sister chromatids are the two identical copies of a single chromosome that are produced during DNA replication. They are held together by proteins called cohesins, primarily at a region known as the centromere, until they are separated during anaphase.

What happens to the nuclear envelope and nucleolus at the beginning of mitosis in animal cells?

In animal cells undergoing open mitosis, the nuclear envelope, which encloses the DNA, breaks down into small vesicles at the start of prometaphase. Concurrently, the nucleolus, responsible for ribosome production, also disappears.

What role do microtubules play in mitosis, and how do they interact with chromosomes?

Microtubules form the spindle apparatus during mitosis. They project from opposite ends of the cell (centrosomes) and attach to the chromosomes at their centromeres, specifically at structures called kinetochores, to align and then pull the sister chromatids apart.

What are daughter chromosomes, and when do they form?

Daughter chromosomes are the separated sister chromatids that are pulled to opposite poles of the cell during anaphase. They are considered individual chromosomes once they have been separated.

What is mitotic catastrophe, and what can it lead to?

Mitotic catastrophe is an error that can occur during mitosis. It can lead to the production of an abnormal number of daughter cells (tripolar or multipolar mitosis), programmed cell death (apoptosis), or mutations, some of which can contribute to the development of cancer.

How does mitosis differ between animal and fungal cells regarding the nuclear envelope?

Animal cells typically undergo 'open mitosis,' where the nuclear envelope breaks down before chromosome separation. In contrast, fungal cells generally undergo 'closed mitosis,' where the chromosomes divide within an intact nuclear envelope.

What is mitotic cell rounding, and why is it important for animal cells?

Mitotic cell rounding is a change in shape that most animal cells undergo at the beginning of mitosis, becoming nearly spherical. This rounding is thought to play a protective role by helping to ensure proper alignment of the mitotic spindle and accurate chromosome segregation.

What is binary fission, and in which types of organisms does it occur?

Binary fission is the process by which prokaryotic organisms, such as bacteria and archaea, divide. Unlike mitosis, it does not involve a nucleus and is a simpler form of cell division.

Who is credited with coining the term 'mitosis', and what is its etymological origin?

The term 'mitosis' was coined by Walther Flemming in 1882. It is derived from the Greek word 'mitos,' meaning 'warp thread,' likely referring to the thread-like appearance of chromosomes during the process.

What are the three subphases of interphase, and what is the primary event occurring in each?

Interphase, the preparatory phase before mitosis, is divided into three subphases: G1 (first gap) for cell growth and protein synthesis, S (synthesis) for DNA replication, and G2 (second gap) for further growth and preparation for mitosis.

What is the G0 phase, and what types of cells typically enter it?

The G0 phase is a state where cells temporarily or permanently exit the cell cycle and stop dividing. Cells like human heart muscle cells and neurons often enter G0 phase after differentiating to perform specialized functions, though some can re-enter the cycle.

What are the two main processes for repairing DNA double-strand breaks during interphase?

During interphase, DNA double-strand breaks can be repaired by non-homologous end joining (NHEJ), which is active in all phases, or by homologous recombinational repair (HRR), which is more accurate and active during the S and G2 phases when sister chromatids are available.

What is the function of the preprophase stage, and in which organisms is it observed?

The preprophase stage, observed only in plant cells, prepares the cell for mitosis by forming a preprophase band of microtubules and actin filaments that marks the future plane of cell division. It also involves the migration of the nucleus to the cell's center.

What is the significance of the metaphase plate in mitosis?

The metaphase plate is an imaginary plane located at the equatorial midline of the cell where chromosomes align during metaphase. This alignment ensures that when the sister chromatids separate, each daughter cell will receive an identical set of chromosomes.

What is the metaphase checkpoint, and what does it ensure?

The metaphase checkpoint is a critical control point in mitosis that verifies that all chromosomes are properly aligned at the metaphase plate and that their kinetochores are correctly attached to the spindle microtubules. This ensures accurate chromosome segregation.

What is nondisjunction during anaphase, and what are its consequences?

Nondisjunction is an error where sister chromatids fail to separate properly during anaphase. This results in one daughter cell receiving both chromatids (leading to trisomy) and the other receiving none (leading to monosomy) for that specific chromosome.

What is anaphase lag, and what is its typical outcome?

Anaphase lag occurs when a chromatid's movement is impeded during anaphase, often due to improper spindle attachment. This lagging chromatid is usually excluded from both daughter nuclei, leading to a monosomic state for that chromosome in one of the resulting cells.

What is endoreduplication, and what does it lead to?

Endoreduplication is a process where chromosomes duplicate, but the cell does not subsequently divide. This results in cells with multiple sets of chromosomes (polyploidy) or, in some cases, polytene chromosomes.

What is endomitosis, and how does it differ from endoreduplication?

Endomitosis is a variation of endoreduplication where cells replicate their chromosomes but prematurely terminate mitosis without dividing. The replicated chromosomes remain within the original nucleus, and the cell may re-enter the cycle, increasing its chromosome number over time.

What is amitosis, and in which tissues is it observed?

Amitosis is a form of cell division that results in a random distribution of parental alleles. It is observed in certain organisms like ciliates and in specific animal tissues, such as placental tissues.

What is the mitotic count or mitotic index, and why is it important in histopathology?

The mitotic count, or mitotic index, refers to the rate at which cells are undergoing mitosis within a tissue sample. It is a crucial parameter in histopathology for diagnosing diseases, particularly for assessing the aggressiveness of tumors.

What are the key functions of mitosis in multicellular organisms?

Mitosis serves several vital functions, including facilitating development and growth from a single cell (like a zygote) to a complex organism, replacing old or damaged cells (like skin cells and red blood cells), enabling regeneration of lost body parts, and supporting asexual reproduction in some species.

What distinguishes 'open' mitosis from 'closed' mitosis?

The primary distinction lies in the behavior of the nuclear envelope. In 'open' mitosis, the nuclear envelope disintegrates before chromosome separation, while in 'closed' mitosis, the nuclear envelope remains intact throughout the process.

What is orthomitosis and pleuromitosis, and what do they refer to?

Orthomitosis and pleuromitosis are classifications based on the symmetry of the spindle apparatus during metaphase. Orthomitosis describes an axially symmetric (centered) spindle, whereas pleuromitosis refers to eccentric spindles with bilateral symmetry.

What is the significance of mitotic cell rounding in epithelial and epidermal cells?

In epithelial and epidermal cells, mitotic cell rounding is correlated with proper alignment of the mitotic spindle and the correct positioning of daughter cells after division. Suppressing this rounding can lead to spindle defects and inaccurate chromosome capture.

How does the actomyosin cortex contribute to mitotic cell rounding?

The actomyosin cortex, composed of actin and myosin, reorganizes during mitosis to rigidify the cell periphery and generate internal hydrostatic pressure. This process is crucial for rounding up the cell, especially when confined by surrounding tissues.

What is mitotic recombination, and how does it relate to DNA repair?

Mitotic recombination is a process that can repair DNA damages, particularly double-strand breaks. Cells irradiated in the G1 phase primarily use recombination between homologous chromosomes, while those irradiated in G2 phase use sister-chromatid recombination.

What is the evolutionary relationship between mitosis and meiosis?

Mitosis is considered a more ancient process, likely arising early in eukaryotic evolution. Meiosis, being more complex, may have evolved later from mitosis, although both processes might have evolved in parallel from ancestral prokaryotic mechanisms.

Which form of mitosis is considered the most primitive, and why?

Closed intranuclear pleuromitosis is considered the most primitive form of mitosis. This is because it shares similarities with bacterial cell division and involves the spindle apparatus forming within an intact nucleus.

How can mitotic cells be visualized microscopically?

Mitotic cells can be visualized microscopically by staining them with fluorescent antibodies and dyes. These stains highlight specific cellular structures, making the stages of mitosis observable.

What is the role of the spindle checkpoint in ensuring accurate mitosis?

The spindle checkpoint, also known as the metaphase checkpoint, monitors the attachment of chromosomes to the mitotic spindle. It prevents the cell from progressing to anaphase until all chromosomes are correctly aligned and attached, thereby preventing aneuploidy.

What are the consequences of errors in mitosis, such as nondisjunction or multipolar mitosis?

Errors in mitosis, like nondisjunction (failure of sister chromatids to separate) or multipolar mitosis (division into more than two cells), can lead to aneuploid cells with incorrect chromosome numbers. This condition is often associated with developmental issues, non-viable embryos, and the development of cancer.

What is the function of the centrosome in animal cell mitosis?

Centrosomes, typically found near the nucleus in animal cells, act as microtubule-organizing centers. They duplicate before mitosis and move to opposite poles of the cell, organizing the formation of the mitotic spindle apparatus.

What is a phragmoplast, and where is it found?

A phragmoplast is a microtubule structure that forms in plant cells during cytokinesis. It plays a role in the formation of the cell plate, which eventually develops into the new cell wall separating the two daughter cells.

What is the difference between cytokinesis in animal cells and plant cells?

In animal cells, cytokinesis involves the formation of a cleavage furrow that pinches the cell membrane inward to divide the cytoplasm. In plant cells, a cell plate forms in the middle of the cell and grows outward to create a new cell wall.

What is the 'mitotic bookmarking' phenomenon mentioned in relation to gene transcription?

Mitotic bookmarking refers to the process where certain transcription factors remain associated with chromosomes during mitosis. This association is thought to help re-establish gene expression patterns in the daughter cells after mitosis is complete.

What is the role of cyclins and cyclin-dependent kinases (CDKs) in the cell cycle?

Cyclins and CDKs are key regulators of the cell cycle. They form complexes that control the progression through different phases, including the preparation for and execution of mitosis, by phosphorylating target proteins.

What is the typical lifespan of red blood cells, and how are new ones produced?

Red blood cells have a short lifespan of approximately three months. New red blood cells are produced through mitosis, ensuring a continuous supply to replace the older ones.

How does mitosis contribute to the regeneration of body parts in organisms like starfish?

Mitosis is the fundamental process by which new cells are generated for tissue repair and regeneration. For example, a starfish can regrow a lost arm through the continuous mitotic division of cells in the affected area.

What is the biological basis for the growth of a multicellular organism from a single cell?

The growth of a multicellular organism from a single cell, such as a zygote, is achieved through repeated mitotic cell divisions. Mitosis increases the number of cells, allowing for the development of tissues, organs, and the entire organism.

What is the significance of the 'lag-type mitosis' in the context of cervical cancer?

Lag-type mitosis, characterized by unattached condensed chromatin within the mitotic figure, is noted as a potential marker. It has been associated with a high risk of human papillomavirus infection-related cervical cancer.

What are the potential consequences if a cell's DNA is damaged or a phase is incomplete, according to the text regarding interphase?

The text suggests that interphase plays a crucial role in preventing the progression of cells with damaged DNA or incomplete phases. Failure in these interphase checkpoints could potentially lead to the production of cancerous cells.

What is the function of kinetochore microtubules during mitosis?

Kinetochore microtubules are specialized microtubules that search for and attach to the kinetochores on the centromeres of chromosomes during prometaphase. They are responsible for moving the chromosomes towards the metaphase plate and then pulling the sister chromatids apart during anaphase.

What is the role of motor proteins in mitosis?

Motor proteins, often found within the kinetochore structure, utilize energy from ATP to 'crawl' along microtubules. This activity, along with microtubule polymerization and depolymerization, generates the forces necessary to separate sister chromatids during anaphase.

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What is Mitosis?

Core Process

Mitosis is a critical part of the cell cycle in eukaryotic cells. It involves the replication and subsequent separation of duplicated chromosomes into two new nuclei. This process ensures that each daughter cell receives an identical set of chromosomes, maintaining genetic stability across cell generations.^[1]^[2]

Cell Cycle Integration

Mitosis is preceded by the S phase of interphase, during which DNA replication occurs. Following mitosis, the cell undergoes telophase and cytokinesis, which divide the cytoplasm, organelles, and cell membrane to form two distinct daughter cells. Together, mitosis and cytokinesis constitute the M phase of the cell cycle, resulting in two genetically identical daughter cells.^[2]^[3]

Mitotic Errors

Errors during mitosis can lead to abnormal cell division, such as tripolar or multipolar mitosis. These errors can result in non-viable embryos, induce programmed cell death (apoptosis), or cause mutations that may contribute to the development of cancers.^[7]^[8]

Historical Discovery

Early Observations

Descriptions of cell division date back to the 18th and 19th centuries. German botanist Hugo von Mohl accurately described cell division in green algae in 1835. In animal cells, mitosis was first identified in frog, rabbit, and cat cornea cells in 1873 by Wacław Mayzel.^[13]^[18]

Naming the Process

The term "mitosis" was coined by German anatomist Walther Flemming in 1882. It derives from the Greek word "mitos," meaning "warp thread," referencing the thread-like appearance of condensing chromosomes. Alternative terms like "karyokinesis" (nuclear division) and "equational division" have also been used.^[23]^[24]

Stages of Mitosis

Preprophase (Plants)

Unique to plant cells, this stage involves the migration of the nucleus to the cell center and the formation of a preprophase band of microtubules, marking the future division plane. This occurs before prophase begins.^[38]

Prophase

Chromatin fibers condense into visible chromosomes, each consisting of two sister chromatids joined at the centromere. The nucleolus disappears, and the mitotic spindle begins to form from centrosomes.^[40]

Prometaphase

The nuclear envelope disintegrates (in open mitosis), allowing microtubules to invade the nuclear space. Kinetochore microtubules attach to chromosomal kinetochores, initiating chromosome movement.^[45]

Metaphase

Centrosomes reach opposite poles, and chromosomes align along the metaphase plate at the cell's equator. The spindle assembly checkpoint ensures proper attachment and alignment before proceeding.^[49]^[51]

Anaphase

Sister chromatids separate, becoming daughter chromosomes. These are pulled towards opposite poles by shortening kinetochore microtubules, while polar microtubules elongate the cell.^[52]

Telophase

This stage reverses prophase events. New nuclear envelopes form around the separated chromosome sets, which decondense. The cell elongates further, and the nucleoli reappear, completing nuclear division.^[54]

Cytokinesis: Completing Division

Animal Cells

In animal cells, cytokinesis involves the formation of a cleavage furrow. A contractile ring of actin and myosin pinches the cell membrane inward between the two nuclei, eventually separating the cytoplasm into two daughter cells.^[55]

Plant Cells

Plant cells form a cell plate in the center of the phragmoplast, derived from Golgi vesicles. This cell plate develops into a new cell wall, dividing the parent cell into two daughter cells.^[39]

Multinucleated Cells

In some organisms and specific cell types, mitosis may occur without subsequent cytokinesis, leading to the formation of multinucleated cells, known as coenocytes.^[57]

Biological Significance

Growth and Development

Mitosis is fundamental for the growth of multicellular organisms, increasing cell numbers from a single zygote to a complex body. It also facilitates the replacement of old or damaged cells, maintaining tissue integrity.^[58]

Repair and Renewal

Many tissues, like skin and the digestive tract lining, constantly shed cells. Mitosis ensures a continuous supply of new, genetically identical cells to replace those lost, crucial for healing and tissue maintenance.^[58]

Asexual Reproduction

For many unicellular organisms and some multicellular ones, mitosis is the primary mode of asexual reproduction. It allows for the creation of genetically identical offspring, ensuring rapid population growth under favorable conditions.^[59]

Variations in Mitosis

Forms of Division

Mitosis varies across eukaryotes based on nuclear envelope behavior (open, closed, semiopen) and spindle symmetry (orthomitosis, pleuromitosis). Closed intranuclear pleuromitosis is considered the most primitive form.^[9]

Closed Intranuclear Pleuromitosis: Typical in Foraminifera, fungi, and some protists.
Closed Extranuclear Pleuromitosis: Found in Trichomonadida and Dinoflagellata.
Closed Orthomitosis: Observed in diatoms, ciliates, yeasts, and some fungi.
Semiopen Pleuromitosis: Characteristic of most Apicomplexa.
Semiopen Orthomitosis: Seen in some amoebae and green flagellates.
Open Orthomitosis: Common in mammals, metazoa, and land plants.

Mitotic Errors

Errors like nondisjunction (failure of sister chromatids to separate) or anaphase lag (chromatid lagging behind) can lead to aneuploidy (abnormal chromosome numbers). Endoreduplication occurs when chromosomes duplicate but the cell fails to divide, resulting in polyploid cells.^[68]

Nondisjunction: Leads to trisomy or monosomy in daughter cells.
Anaphase Lag: Results in a lost chromatid and a monosomic daughter cell.
Endoreduplication: Chromosome duplication without cell division, leading to polyploidy.
Endomitosis: Chromosome replication within an intact nucleus, increasing chromosome number.

Diagnostic Significance

The rate and appearance of mitosis (mitotic index) are crucial diagnostic markers in histopathology, particularly for assessing tumor aggressiveness. Atypical mitotic figures can indicate high-risk conditions.^[74]^[75]

Visualizing Mitosis

Plant Cell Preprophase

Early prophase in plant cells, showing the nucleus and condensing chromosomes within a microtubule matrix.

Early prophase: Polar microtubules form a matrix around the intact nucleus, with condensing chromosomes (blue) and centromeres (red).

Animal Cell Prometaphase

Early prometaphase in animal cells, where the nuclear membrane breaks down, allowing microtubule interaction with chromosomes.

Early prometaphase: Nuclear membrane disassembly allows microtubules to interact with kinetochores on centromeres.

Animal Cell Metaphase

Metaphase shows centrosomes at poles and chromosomes aligned at the metaphase plate, visualized with fluorescent staining.

Metaphase: Chromosomes aligned at the metaphase plate, with centrosomes at opposite poles, forming the mitotic spindle.

Animal Cell Anaphase

Anaphase features sister chromatids separating and moving to opposite poles, driven by microtubule dynamics.

Anaphase: Sister chromatids separate into daughter chromosomes, pulled towards opposite poles of the cell.

Animal Cell Telophase

Telophase reverses prophase events, with new nuclear envelopes forming around decondensing chromosomes.

Telophase: New nuclear envelopes form around the decondensing chromosome sets, completing nuclear division.

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References

"Notes and memoranda: The late professor von Mohl". Quarterly Journal of Microscopical Science, v. XV, New Series, p. 178â181, 1875. link.

Bernstein, H., Bernstein, C. Evolutionary origin and adaptive function of meiosis. In "Meiosis", Intech Publ (Carol Bernstein and Harris Bernstein editors), Chapter 3: 41â75 (2013).

A full list of references for this article are available at the Mitosis Wikipedia page

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Mitosis Unveiled

💡 Dive in with Flashcard Learning! 💡

What is Mitosis? ℹ️

🧬 Core Process

🔄 Cell Cycle Integration

⚠️ Mitotic Errors

Historical Discovery 📜

🔬 Early Observations

🏷️ Naming the Process

Stages of Mitosis ➡️

🌿 Preprophase (Plants)

⏳ Prophase

🔗 Prometaphase

📏 Metaphase

↔️ Anaphase

🏁 Telophase

Cytokinesis: Completing Division ✂️

🤏 Animal Cells

🧱 Plant Cells

🏢 Multinucleated Cells

Biological Significance 💡

📈 Growth and Development

🩹 Repair and Renewal

🌱 Asexual Reproduction

Variations in Mitosis 🔀

🌐 Forms of Division

❌ Mitotic Errors

🔬 Diagnostic Significance

Visualizing Mitosis 🖼️

🌱 Plant Cell Preprophase

🔗 Animal Cell Prometaphase

📏 Animal Cell Metaphase

↔️ Animal Cell Anaphase

🏁 Animal Cell Telophase

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📜 Important Notice

Dive in with Flashcard Learning!

What is Mitosis?

Core Process

Cell Cycle Integration

Mitotic Errors

Historical Discovery

Early Observations

Naming the Process

Stages of Mitosis

Preprophase (Plants)

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Cytokinesis: Completing Division

Animal Cells

Plant Cells

Multinucleated Cells

Biological Significance

Growth and Development

Repair and Renewal

Asexual Reproduction

Variations in Mitosis

Forms of Division

Mitotic Errors

Diagnostic Significance

Visualizing Mitosis

Plant Cell Preprophase

Animal Cell Prometaphase

Animal Cell Metaphase

Animal Cell Anaphase

Animal Cell Telophase

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Important Notice