Why interphase is the most frequently observed phase

For this reason, it should be borne in mind that the phases of mitosis are arbitrary designations and serve only as a tool for studying and describing the entire process of cell division. Interphase - Between mitotic divisions, a normal resting or actively growing cell exists in a state known as interphase , in which the chromatin forms a highly diffuse, fibrous network that is being continuously transcribed by enzymes within the nucleus Figure 1 a.

Before the cell enters the mitosis sequence, it first undergoes a DNA synthesis or S phase where each chromosome is duplicated to produce an identical pair of sister chromatids joined together by a specific DNA sequence known as a centromere. Centromeres are crucial to segregation of the daughter chromatids during mitosis.

Prophase - The first stage of mitosis is known as prophase , where the nuclear chromatin starts to become organized and condenses into thick strands that eventually become chromosomes observable in the optical microscope Figure 1 b. The nucleoli, primarily responsible for the production of ribosomal RNA, begin to disappear as the chromosomes condense. During prophase, major changes also occur in the cytoplasm, including disassembly of the cytoskeleton components based on tubulin cytoplasmic microtubules.

The tubulin monomers are dynamically redirected by the dividing cell to form the main component of the mitotic apparatus, the mitotic spindle , which is bounded by the centrosomes and begins to appear along the periphery of the nuclear membrane.

Prometaphase - Late prophase, or prometaphase , begins with the disruption of the nuclear envelope, which is broken down into small membrane vesicles that closely resemble the endoplasmic reticulum and tend to remain visible around the mitotic spindle.

During this period the chromosomes continue to condense and gradually shorten and thicken until they have completely formed the units that will undergo mitosis. The nucleolus, which may still be present in some cells, also completely disappears in prometaphase.

In the absence of the nuclear membrane, the mitotic spindle microtubules are now free to enter the nuclear region, and formation of specialized protein complexes called kinetochores begins on each centromere.

These complexes become attached to some of the spindle microtubules, which are then termed kinetochore microtubules. Other microtubules in the spindle not attached to centromeres are termed polar microtubules and these help form and maintain the spindle structure along with astral microtubules, which remain outside the spindle.

Metaphase - Perhaps the most recognizable phase of mitosis is termed metaphase , a stage where the chromosomes, attached to the kinetochore microtubules, begin to align in a single plane known as the metaphase plate midway between the spindle poles see Figure 1 c.

The kinetochore microtubules exert tension on the chromosomes, which move back and forth in rapid erratic motion as a result, and the entire spindle-chromosome complex is now ready for the next event, separation of the daughter chromatids. Metaphase, one of the most critical stages in mitosis, occupies a substantial portion of the division cycle.

The primary reason for this extended interval is that dividing cells pause until all of their chromosomes are completely aligned at the metaphase plate. During interphase, the Golgi apparatus accumulates enzymes, structural proteins, and glucose molecules prior to breaking into vesicles and dispersing throughout the dividing cell. During telophase, these Golgi vesicles are transported on microtubules to form a phragmoplast a vesicular structure at the metaphase plate.

There, the vesicles fuse and coalesce from the center toward the cell walls; this structure is called a cell plate. As more vesicles fuse, the cell plate enlarges until it merges with the cell walls at the periphery of the cell. Enzymes use the glucose that has accumulated between the membrane layers to build a new cell wall. The Golgi membranes become parts of the plasma membrane on either side of the new cell wall Figure 4. Figure 5 shows approximately how long a cell spends in each stage of the cell cycle:.

Figure 5. The cell cycle consists of interphase and the mitotic phase. During interphase, the cell grows and the nuclear DNA is duplicated. Interphase is followed by the mitotic phase. During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei.

The cytoplasm is usually divided as well, resulting in two daughter cells. This video reviews all the steps of mitosis; seeing it all together is a great review at this stage. Answer the question s below to see how well you understand the topics covered in the previous section.

This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times. Use this quiz to check your understanding and decide whether to 1 study the previous section further or 2 move on to the next section. Privacy Policy.

Skip to main content. The kinetics of isthmal cells in mouse antrum were examined in three ways: the duration of cell cycle and DNA-synthesizing S stage was measured by the 'fraction of labelled mitoses' method; the duration of interphase and mitotic phases was determined from how frequently they occurred; and mice were killed at various intervals after an intravenous injection of 3H-thymidine to time the acquisition of label by the various phases of mitosis.

The duration of the isthmal cell cycle was found to be Estimates for the duration of the G1 and G2 stages were 6. This last stage is all about prepping the cell for mitosis or meiosis. During G2, the cell has to grow some more and produce any molecules it still needs to divide. Interphase was formerly called the resting phase. One reason why the interphase is most important is that it takes up ninety percent of the cell cycle, its parts are G1, DNA synthesis and G2, without interphase, no part of the cell cycle can be possible.

Interphase is the most frequently observed stage, because most cells are not actively dividing at any given moment. The synthesis phase of interphase takes the longest because of the complexity of the genetic material being duplicated. Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In anaphase, the shortest stage of mitosis, the sister chromatids break apart, and the chromosomes begin moving to opposite ends of the cell.

By the end of anaphase, the 2 halves of the cell have an equivalent collection of chromosomes. Interphase is the longest part of the cell cycle. This is when the cell grows and copies its DNA before moving into mitosis. During mitosis, chromosomes will align, separate, and move into new daughter cells. The prefix inter- means between, so interphase takes place between one mitotic M phase and the next.