What Must Happen Before A Cell Can Begin Mitosis?
A frog, the yeast in bread dough, and an intestinal cell all have cells that undergo mitosis. Each cell comprises a set of duplicated chromosomes, and mitosis ensures that each daughter cell has identical genetic information.
Before a cell can begin mitosis, several events must happen. They are called prophase, metaphase, anaphase, and telophase.
Prophase
Your intestines, yeast in bread dough, and a developing frog all have cells that carry out mitosis, the process of dividing to produce two genetically identical cells. This division ensures that each daughter cell gets a full set of chromosomes, so it can grow and develop properly.
Before a cell can begin mitosis, several things must happen. First, the nucleus must be replicated. This means that the genome, organelles (such as the centrosome), and other essential components of the cell must be replicated.
Second, chromatin fibers must condense into chromosomes that can be seen under the microscope. Chromosomes look like X-shaped molecules. Each chromosome is a pair of sister chromatids joined at a special centromere.
Then, a specialized protein structure called a kinetochore form at each centromere, where it attracts and binds microtubules. These microtubules help chromosomes move and separate.
Third, the centrosomes begin to move toward opposite poles of the cell. This movement of the chromosomes is called anaphase, and it occurs over a few minutes as the microtubules attached to the kinetochores shorten and pull the sister chromatids apart.
The spindle fibers moving the chromosomes out of the cell break up, and a new nuclear membrane forms at the ends of each daughter cell. These components will assemble the cytoskeleton for each of the two new cells. Once the cytoskeleton is assembled, each daughter cell will start to divide.
Metaphase
Before a cell can begin mitosis, the number of chromosomes in the parent cell must double. This is done so that the parent and daughter cells are identical to one another and that they have the same chromosome composition (number of genes) as the original cell.
The chromosomes in the nucleus are long, coiled molecules of DNA that contain proteins. They are organized into chromosomes, which comprise two sister chromatids (two halves of a chromosome).
Once the number of chromosomes in a parent cell has doubled, mitosis can begin. In this stage, a cell is lined up on a plane called the metaphase plate, where all the chromosomes are ready to divide.
During this phase, the chromosomes are under tension from the mitotic spindle and are captured by microtubules that extend from opposite mitotic spindle poles. They are oriented on the metaphase plate, also known as the equatorial plane of the cell.
While in metaphase, chromosomes are connected to the microtubules by proteins called cohesins. These proteins are attached to the kinetochores, which extend from the opposite side of each centrosome.
A protein called an anaphase-promoting complex is activated to help the chromosomes align correctly at the equatorial plane of the metaphase plate and to ensure that all of the microtubules are in the correct position. This is a crucial checkpoint that must be met before the cohesins can tear the chromosomes apart and the chromosomes can be separated into their separate chromatids.
The sister chromatids are then separated, and the non-kinetochore microtubules slide against each other at the metaphase plate, creating a visible cell elongation. The cell then condenses and splits into two identical daughter cells, each with its nucleus and cytoplasm.
Anaphase
Anaphase is the phase in which chromosomes are separated and moved to opposite ends of the cell. This allows a complete set of duplicate chromosomes to be located at each pole, which means two daughter cells can be made.
Before a cell can begin mitosis, there must be copies of each DNA strand in the nucleus. This is necessary so that each daughter cell can have the same number and kind of chromosomes as the parent cell.
In metaphase, chromatids line up along the center of the cell and are held together by a protein “glue.” This glue breaks down during anaphase, allowing the sister chromatids to separate. They are then pulled apart by the mitotic spindle to opposite ends of the cell.
The movement of the chromosomes in anaphase depends on motor proteins that walk along microtubules. These microtubules are not attached to the chromosomes but to the centrosome.
When the chromatids separate, the microtubules not attached to the chromosomes elongate and push the chromosomes away from the centrosome. These microtubules are called kinetochore microtubules.
These microtubules create a central force that pulls the chromosomes to opposite poles of the cell (anaphase A). This is facilitated by minus-end-directed motor proteins interacting with the astral microtubules and the cell’s cortex.
This process is also mediated by motor proteins at the centromere that moves the chromosomes to opposite poles. These motor proteins use a bundle of antiparallel overlap microtubules to push the chromosomes toward the poles.
The two chromatids at each pole are joined by a special string of DNA known as the chiasma. This chromosome shape changes during anaphase to a Y-like or a V-like shape.
Telophase
Before a cell can begin mitosis, certain events must happen. First, each chromosome must be duplicated or synthesized. This process involves a complex set of chemical reactions within the cell to produce two identical sets of chromosomes joined by a specific DNA sequence called a centromere (see Figure 3-14G).
Second, those duplicated chromatids must be pulled away from each other and reach opposite poles, known as polar regions. This is important because the cells will then be divided into two daughter cells, each with a complete set of chromosomes.
Third, a nuclear membrane must form around each set of chromosomes to separate the nucleus from the cytoplasm, and a cleavage furrow must start to develop along the cell membrane to mark where two new daughter cells will pinch off from the parent cell. This pinching is a process called cytokinesis and occurs in animal and plant cells.
Fourth, the chromosomes must be decondensed from their extended, crowded form and become more diffuse. Chromatin, the network of proteins that bind to the chromosomes during DNA synthesis, must undergo a series of chemical reactions to uncoil and return to a more uniform, homogeneous appearance.
Finally, the spindle fiber microtubules must dissolve, and the nuclear envelopes that formed during anaphase must re-form, which will contain the duplicated chromosomes and help separate them into daughter cells.
Once these steps are completed, the cell is ready to divide again. The sister chromatids are then pulled to opposite poles, the nuclear membranes form around them, and the nucleoli reappear in each of the two daughter cells. The process is called cytokinesis and begins a short resting period before the cell enters a new phase of mitosis, known as interphase.
Cytokinesis
The cell must undergo a series of preparatory steps before it can begin mitosis. One of these is called cytokinesis, or “cell motion.” This process involves physically separating the cellular components into two daughter cells.
During cytokinesis, the parent cell divides to produce identical daughter cells that contain a full complement of genetic information. This is essential for an organism to grow and develop properly.
In animal cells, cytokinesis is contractile. The membrane pinches at the equator, forming a cleavage furrow that will eventually pinch off the cell to form two daughter cells. The cleavage furrow is formed by the actin filaments of the cytoskeleton.
Plant cells, on the other hand, cannot be divided this way because their cell walls are too stiff. Instead, a structure called a cell plate forms down the middle of the cell. This new cell wall grows out from vesicles of a protein called polysaccharides and glycoproteins.
This early cell plate is controlled by the phragmoplast, which contains the remains of the mitotic spindle that transports these vesicles to the center of the cytoskeleton. This phragmoplast then controls the growth of this cell plate until it reaches the point determined by a cytoskeleton band called the preprophase band.
As the cell grows, the preprophase band disappears, and a new cytoskeleton, known as a chromosomal coat, forms. This chromosomal coat is important because it determines the position of the cell plate.
The chromosomes are pulled apart, and each copy is assigned to a different daughter cell. This is vital to the process of asexual reproduction, as well as for the replacement of damaged and worn-out cells. If the chromosomes are not distributed to the correct daughter cells, the result can be cell death or cancer.
What Must Happen Before A Cell Can Begin Mitosis? Guide To Know
Before a cell can begin mitosis, it must undergo several preparatory stages. These stages are collectively referred to as interphase and are divided into three distinct sub-phases: G1, S, and G2.
During the G1 phase, the cell grows in size, synthesizes RNA and protein, and prepares to replicate its DNA. This phase is also characterized by the synthesis of new organelles, such as ribosomes, and the production of energy through aerobic respiration or fermentation.
During the S phase, DNA replication takes place. The cell’s DNA helix unwinds, and enzymes move along the strands, building new complementary strands using the existing ones as templates. As a result of DNA replication, each chromosome in the cell is duplicated and consists of two identical sister chromatids held together by a centromere.
During the G2 phase, the cell continues to grow and prepare for mitosis. The cell synthesizes additional proteins and organelles and checks its DNA for errors that might have occurred during replication. This phase is also characterized by initiating the assembly of the spindle fibers, which are responsible for separating the sister chromatids during mitosis.
Once a cell has completed the interphase stages, it is ready to begin mitosis. During mitosis, the duplicated chromosomes condense and become visible as distinct structures under a microscope. The spindle fibers attach to the kinetochores of the chromosomes and begin to pull them apart, separating the sister chromatids and ensuring that each daughter cell receives an exact copy of the genetic material.
Finally, cytokinesis occurs, dividing the cell’s cytoplasm and creating two new daughter cells, each with its nucleus containing a complete set of chromosomes.
FAQ’s
What must happen before mitosis can begin ?
What must occur before a cell can start the mitotic process? There needs to be chromosomal duplication. The chromosomes, or genetic material, must be copied during interphase for mitosis to start.
What happens before the first stage of mitosis?
Prophase, the first stage of mitosis, sees the recruitment of condensin and the start of the condensation process that lasts until metaphase. In the majority of species, prophase allows the resolution of the individual sister chromatids by mainly removing cohesin from the arms of the sister chromatids.
What must happen before mitosis and meiosis begins?
Cells must pass through interphase before dividing, either through mitosis or meiosis. During interphase, a cell’s contents double. The organelles are duplicated together with all of the chromosomes.
What must happen before meiosis can begin?
Each chromosome’s DNA is copied before meiosis has started. The two identical copies of DNA that are produced as a result of this replication are known as “sister chromatids,” and they are connected to one another by a section of the chromosome known as the centromere.
What process occurs before and after mitosis?
Nuclear division occurs during mitosis, a process in which duplicated chromosomes are separated and distributed among daughter nuclei. After mitosis, a process known as cytokinesis, in which the cytoplasm is divided and two daughter cells are created, usually occurs, the cell will divide.
