Cell Biology - Biology

There are many ways that mitosis and meiosis differ, in this question we are primed to look at the differences in the end products of each type of cell division.

Mitosis creates two new cells that are identical to the parent cell (diploid). Meiosis creates 4 new cells with half the genetic information (haploid) in each cell, and the cells are nonidentical to the parent cell and to their sister cells.

Prophase- spindles forming, chromosomes condense, and the nuclear membrane begins to break down

Prometaphase- microtubules grow

Metaphase- chromatids are lined up in the center of the cell on the equatorial plate

Anaphase- the two chromatids of the chromosome are pulled apart at the centromere

Telophase- new nuclear membranes form around each set of chromosomes, the spindles break down, and chromosomes decondense

Prophase- spindles forming, chromosomes condense, and the nuclear membrane begins to break down

Prometaphase- microtubules grow

Metaphase- chromatids are lined up in the center of the cell on the equatorial plate

Anaphase- the two chromatids of the chromosome are pulled apart at the centromere

Telophase- new nuclear membranes form around each set of chromosomes, the spindles break down, and chromosomes decondense

Prophase- spindles forming, chromosomes condense, and the nuclear membrane begins to break down

Prometaphase- microtubules grow

Metaphase- chromatids are lined up in the center of the cell on the equatorial plate

Anaphase- the two chromatids of the chromosome are pulled apart at the centromere

Telophase- new nuclear membranes form around each set of chromosomes, the spindles break down, and chromosomes decondense

It is important to remember that interphase is not actually a part of mitosis, but rather is the preparation phase, setting the stage for mitosis to occur. Cells spend most of their time in this phase. During interphase the cells make copies of its structures and duplicates its chromosomes during DNA synthesis. The G1, S phase, and G2 phase all make up interphase, (if you remember from the previous question).

Prophase is the first stage of mitosis. The cell cytoplasm and nucleus undergo several changes. At this point the mitotic spindle is forming but the nucleus is still intact. In this phase the chromosomes become tightly packed and the nucleoli disappear. Each chromosome is paired with its sister chromatid joined in the middle at the centromere.

During premetaphase the nuclear envelop has broken down and this allows the spindle, or the microtubules, begin to attach to the chromosomes at the kinetochore. The microtubules begin to put force on the chromosomes to begin moving them to the middle of the cell.

The condensed chromosomes are aligned on the metaphase plate (an imaginary line in the middle of the cell). They align this way because of the microtubules that are pulling them to the opposite sides.

Anaphase is where the duplicated chromosomes split, disconnected at the centromere, and each sister chromatid is moved towards opposite sides of the cells.

Important indications that the cell is in telophase are that the chromosomes have been moved towards the opposite sides of the cell. The nuclear envelope does begin to form around the new respective nucleus of each daughter cell and the cell itself begins the stages of cytokinesis, or this splitting of the cell into two daughter cells.

Cytokinesis is the division of the cell into two respective daughter cells. Cytokinesis can start as early as anaphase and moves through with telophase. The most important thing in this part of the process is to make sure that there is one nucleus in each new cell being formed. A protein filament ring, called the contractile ring, causes the middle of the cell to shrink and pinch off to form the two separate daughter cells.

The cell in the picture about is in the prometphase stage. Key indicators of this phase are the breakdown of the nuclear envelope around the genetic material and the spindle beginning to interact with the chromosomes.

The cell pictured above is in prophase. Key indicators that the cell is in this stage are that the nuclear envelope is still intact and chromosomes have become condensed and paired up with sister chromatids.

Interphase would be first as this is the part of the cycle cycle that the cell prepares to enter Mitosis. The key indicators of prophase are that the nuclear envelope is still intact and the chromosomes are beginning to pair up sister chromatids. The mitotic spindle is also beginning to form. Premetaphase, the next phase, is when the spindle has attached itself to the respective chromosomes and they begin to migrate to the center of the cell. In Metaphase the chromosomes have lined up on the mitotic plate and beginning to separate. In anaphase each sister chromatid moves to its respective side of the cell, as it is being pulled there by the mitotic spindle. The last phase of mitosis is telophase, which is indicated by the beginning of the cell splitting into two, called cytokinesis.

Mitosis has only one round of chromosome separation and creates all cells, other than sex cells. For example skin cells. This process ends with two diploid cells that are genetically identical to the parent cell.

Meiosis is the process that generates the cells that occur in sexual reproduction cells, otherwise known as gametes. This process, since it has two rounds of chromosome separation, will end with 4 haploid cells, or half the genetic information of the parent cell.

The correct order to the phases is: prophase, metaphase, anaphase, telophase.

During prophase, the nuclear membrane dissolves and the DNA condenses into chromosomes. The chromosomes travel to the center of the cell during metaphase and align, allowing spindle fibers to bind to the center of each chromosome. The spindle fibers contract during anaphase, separating the sister chromatids and pulling them to opposite poles of the cell. During telophase, the nuclear membrane begins to re-form and a ring of contractile filaments begins to pinch the cytoplasm to create two separate daughter cells (this is known as the cleavage furrow). Following telophase, the daughter cells completely separate; the division of the cytoplasm is called cytokinesis and is often considered a separate event from mitosis.

The process of mitosis involves separating the already duplicated chromosomes (sister chromatids). The parent cell doubled its DNA during the S phase of interphase so that it now has four copies of each gene (two copies of each allele). In humans this is equivalent to two copies of all 23 chromosomes from the mother, and two copies of all 23 chromosomes from the father, sometimes called 2x2n or 4n depending on the textbook.

During division, each chromosome is divided into its component chromatids. The result is a single copy of each chromosome (two copies of each gene, one from the mother and one from the father) in each daughter cell. Because there are two copies of each gene in the daughter cells, they are considered diploid. Sister chromatids are identical genetic copies; separating sister chromatids will result in identical daughter cells.

In contrast, the final product of meiosis is four nonidentical haploid cells. Each daughter cell at the end of meiosis carries only one copy of each gene (haploid) and is nonidentical to the other three daughter cells due to the phenomenon of independent assortment.

Spindle fibers are specialized microtubule structures that guide the movement of chromosomes and chromatids during mitosis. During mitosis, the spindle fibers will bind to a protein complex (known as the kinetochore) at the center of the chromosome. The kinetochore serves as an anchor, allowing the spindle fibers to retract and separate the sister chromatids. Centrioles serve as the opposite anchor point, keeping the other end of the spindle fiber attached to the pole of the cell.

Viscles are small membrane-bound sacs that can be used to transport proteins and other molecules either within the cell, or between the cell and the extracellular matrix. Microfiliments are another component of the cytoskeleton and are frequently associated with motility; the protein actin is a microfiliment.

Recall PMAT mnemonic for remembering the steps in mitosis: prophase, metaphase, anaphase, telophase. Mitosis involves the separation of the (already-duplicated) chromosomes. The chromosomes condense, the mitotic spindle begins to form, and the nuclear envelope begins to break down during prophase. During metaphase, the chromosomes line up on the metaphase plate. In anaphase, the sister chromosomes begin getting pulled to opposite ends of the cell. Telophase is the opposite of prophase, and the cell undergoes cytokinesis.

When a primary oogonium undergoes meiosis, it will only result in one viable germ cell, or egg. The other smaller cells are called polar bodies and typically disappear following division. Spermatogenesis will result in four separate sperm cells, each capable of producing offspring.

Both eggs and sperm are haploid, and both processes can involve crossing over during meiosis.