Mitosis: Cell Division Explained

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Questions and Answers

What cytoskeletal elements participate in mitosis and what is their primary role?

Spindle apparatus and centrosomes (centrioles); they organize and separate chromosomes.

Briefly describe what occurs to the nuclear membrane during prophase and what effect this has on the cell.

The nuclear membrane disintegrates and disappears, which releases the chromosomes into the cytoplasm.

What are the two main events that occur during metaphase to prepare the cell for chromosome segregation?

Chromosomes align at the metaphase plate, and kinetochore fibers attach to the kinetochores of the centromeres.

During anaphase, sister chromatids separate and move to opposite poles. What is the mechanism that facilitates this movement?

<p>Kinetochore fibers shorten, pulling the sister chromatids apart. These filaments are broken by the centromere.</p> Signup and view all the answers

How do daughter cells form during telophase, and what is the state of the chromosomes at this stage?

<p>A nuclear membrane forms around each set of chromosomes, and the chromosomes unwind to form chromatin.</p> Signup and view all the answers

What is the difference between mitosis in eukaryotic cells and in protozoa and fungi?

<p>Some protozoa and fungi undergo open mitosis, where the nuclear membrane disappears, while other eukaryotes have a more closed mitosis.</p> Signup and view all the answers

Starting with a stem cell that has 2n = 4 chromosomes, mitosis results in two daughter cells. How many chromosomes are in each daughter cell?

<p>Each daughter cell will have 2n = 4 chromosomes.</p> Signup and view all the answers

How does cytokinesis differ between animal and plant cells, relating to the structures used?

<p>Animal cells use a contractile ring that forms a cleavage furrow, while plant cells use a phragmoplast to build a cell wall.</p> Signup and view all the answers

Describe the role of the Golgi apparatus in cytokinesis in plant cells.

<p>The Golgi apparatus releases vesicles containing cell wall components that accumulate to form the phragmoplast.</p> Signup and view all the answers

What is the structure comprised of actin and myosin filaments that facilitates cytokinesis in animal cells, and how does it function?

<p>The contractile ring; it shrinks, forming a cleavage furrow that constricts the cell and divides it into two daughter cells.</p> Signup and view all the answers

Why is DNA replication important before mitosis?

<p>DNA replication ensures that each daughter cell receives a complete and identical copy of the genetic information.</p> Signup and view all the answers

What is the significance of the chromosomes reaching maximum condensation during metaphase?

<p>Maximum condensation facilitates proper segregation of chromosomes during anaphase, preventing tangling or breakage.</p> Signup and view all the answers

During anaphase, each sister chromatid becomes an independent chromosome. What event defines this transition?

<p>The separation of the sister chromatids at the centromere.</p> Signup and view all the answers

How does the re-formation of chromatin filaments in telophase relate to the cell's function?

<p>It allows for gene expression to resume in the daughter cells.</p> Signup and view all the answers

What is the role of the kinetochore fibers during metaphase and anaphase?

<p>During metaphase, they attach chromosomes to the spindle apparatus. During anaphase, they shorten to pull the sister chromatids apart.</p> Signup and view all the answers

Describe the relationship between the spindle apparatus and the chromosomes during the different phases of mitosis.

<p>The spindle apparatus attaches to the chromosomes during metaphase, separates them during anaphase, and disassembles during telophase as the chromosomes decondense.</p> Signup and view all the answers

If a cell bypasses the DNA replication stage before mitosis, what would be the likely outcome for the daughter cells?

<p>The daughter cells would have an incomplete set of chromosomes or genetic information.</p> Signup and view all the answers

What is the first visible event in prophase, when observing cell from a microscope?

<p>The condensation of chromatin fibres into chromosomes and nucleolus disappearing.</p> Signup and view all the answers

Give two reasons open mitosis might be advantageous for protozoa and fungi?

<p>Faster cell division, less energy consumption to break down the nuclear envelope.</p> Signup and view all the answers

How does the shape of chromosomes change from metaphase to anaphase, and what causes this change?

<p>From X-like shape in metaphase chromosomes transform in V-Like shape in anaphase when chromatids splits.</p> Signup and view all the answers

Flashcards

Cell Division (M-Phase)

Cell division or M-phase is a relatively short process where a stem cell divides into two identical daughter cells.

DNA Replication

Before mitosis, chromosomes in the form of chromatin filaments are duplicated, giving the mother cell two equal copies of its information.

Mitosis Definition

Mitosis is the period of the cell cycle where the nucleus divides, involving the spindle apparatus and centrosomes.

Prophase Events

Chromatin condenses into visible chromosomes; the nucleolus disappears; centrioles move to opposite poles, forming the spindle apparatus; and the nuclear membrane disintegrates.

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Metaphase

Chromosomes align at the metaphase plate, with kinetochore fibers from the spindle apparatus attached to the centromeres.

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Anaphase

Sister chromatids separate and move to opposite poles as spindle fibers shorten. Each chromatid becomes an independent chromosome.

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Telophase

Chromosomes arrive at the poles and decondense; the nuclear membrane reforms, and the nucleolus reappears.

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Cytokinesis definition

The division of the cytoplasm, distributing organelles, which occurs at the end of telophase.

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Cytokinesis in animal cells

A contractile ring of actin and myosin forms, shrinking to create a cleavage furrow that pinches the cell into two daughter cells.

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Cytokinesis in plant cells

Small vesicles from the Golgi apparatus accumulate and fuse to form a phragmoplast, which grows and becomes a cell wall separating the daughter cells.

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Study Notes

  • Cell division, also known as M-phase, results in one stem cell dividing into two daughter cells.
  • It is a short process.
  • During interphase, DNA replicates, forming chromatin filaments and creating two copies of the mother cell's information.
  • For example, a cell with 2n=4 will undergo DNA replication before mitosis begins.

Definition of Mitosis

  • Mitosis is the phase of the cell cycle where the nucleus divides.
  • It requires the spindle apparatus and centrosomes (centrioles).
  • Most eukaryotic cells (except some protozoa and fungi) exhibit "open mitosis," where the nuclear membrane disintegrates.

Prophase

  • Chromatin condenses into chromosomes.
  • Nucleolus disappears.
  • Diplosome (two centrioles) duplicates during the G2 phase.
  • Each diplosome moves to opposite poles of the cell.
  • Microtubule fibers extend from the diplosomes, creating the spindle apparatus or mitotic spindles.
  • Nuclear membrane breaks down

Metaphase

  • Spindle apparatus attaches to the kinetochores on the centromeres via kinetochore fibers.
  • Chromosomes align at the cell's center on the metaphase or equatorial plate.
  • Chromosomes reach maximum condensation, appearing as X-shaped structures.

Anaphase

  • Spindle fibers shorten as the centromeres divide. Sister chromatids detach and move towards opposite poles.
  • Each sister chromatid becomes an independent chromosome. (duplicated in S-phase)
  • These new chromosomes, now separated, are V-shaped

Telophase

  • Chromosome migration completes and spindle fibers disappear.
  • Nuclear membranes reform around each set of chromosomes.
  • Chromosomes unwind, reverting to chromatin filaments.
  • Nucleolus reappears.

Cytokinesis Definition

  • Cytokinesis is the division of the cytoplasm and the equal distribution of cell organelles.
  • It takes place at the end of the telophase.

Cytokinesis in Animal Cells

  • Occurs in cells without cell walls.
  • A contractile ring of actin and myosin filaments forms around the cell's equator.
  • The contractile ring shrinks, producing a cleavage furrow.
  • Cytoplasm strangulation leads to the separation of the cell into two daughter cells.

Cytokinesis in Plant Cells

  • Occurs in cells with cell walls.
  • Small vesicles from the Golgi apparatus containing cell wall and cell membrane components accumulate at the cell's equator.
  • Vesicles fuse to form a cell plate called the phragmoplast.
  • The phragmoplast grows and forms a new cell wall between the two daughter cells.
  • This leads to the separation of the cell into two daughter cells.

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