7.9
Mitosis And Cytokinesis
In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome d…
Mitosis is a form of cell division where a cell's genetic material is partitioned between two daughter cells.
First, during prophase, nucleic chromatin condenses into x-shaped chromosomes composed of sister chromatid pairs attached at centromere junctions.
Concurrently, the centrosomes migrate to opposite cell sides. As they do so, microtubule rods begin to grow from each, forming a web-like spindle apparatus.
Next, the nuclear envelope dissolves during prometaphase and the protein structures, termed kinetochores, appear on both sides of the centromeres, one for every chromatin.
Once these kinetochores form, extending interior microtubules fasten to them, with each sister chromatid being tethered to a different cell pole.
In metaphase, the spindle apparatus rearranges the chromosomes so that they are oriented in a fixed row along the cell's equator.
With anaphase, kinetochore afixed microtubules shorten and sister chromatids are dragged apart. These and other microtubule dynamics also elongate the cell.
During telophase, the spindle apparatus disbands, chromatids loosen, and nuclear envelopes are reformed.
Finally, the cell is cytoplasmically divided by cytokinesis, forming a pair of cells genetically identical to their precursor.
View the full transcript and gain access to JoVE Core videos
Q1: What is the main purpose of mitosis in cell division?
Mitosis ensures that each daughter cell receives an identical copy of the parent cell's genetic material. This process maintains chromosome number and genetic consistency across generations of cells, which is essential for growth, tissue repair, and asexual reproduction in organisms.
Q2: How does cytokinesis differ from mitosis?
Mitosis divides the nucleus and genetic material, while cytokinesis divides the cytoplasm to physically separate the two daughter cells. Cytokinesis occurs simultaneously with late mitosis, completing cell division by forming a cleavage furrow in animal cells or a cell plate in plant cells.
Q3: What happens to chromosomes during anaphase?
During anaphase, sister chromatids separate and move toward opposite poles of the cell. The spindle fibers shorten, pulling the individual chromatids, now chromosomes, to each end, ensuring that genetic material is equally distributed to the future daughter cells during cell division.
Q4: Why is metaphase important for accurate cell division?
During metaphase, chromosomes align at the cell's equator, allowing spindle fibers to attach properly to kinetochores. This precise alignment ensures that when sister chromatids separate, each daughter cell receives the correct number and type of chromosomes, preventing genetic errors during division.
Q5: What occurs during telophase to complete mitosis?
Telophase reverses the changes of prophase: chromosomes decondense, nuclear envelopes reform around each set of chromosomes, and spindle fibers disappear. This stage prepares each nucleus for the next cell cycle and sets the stage for cytokinesis to physically divide the cell.
Q6: How do molecular factors affecting cell division regulate mitosis?
Molecular factors affecting cell division, such as cyclins and checkpoint proteins, control progression through mitotic stages. These regulatory molecules ensure cells divide only when appropriate and halt division if chromosomes are misaligned or DNA is damaged, maintaining cellular integrity and preventing errors.
Q7: What is the relationship between the cell cycle control system and mitosis?
The cell cycle control system regulates when cells enter and progress through mitosis. This system monitors cellular conditions and DNA integrity, ensuring mitosis occurs only at appropriate times and preventing uncontrolled division that could lead to cellular dysfunction or disease.