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8.1.1. Interphase


The interphase is the longest stage of the cell cycle, and is the period of time that elapses between two successive mitoses. Although the cell is not dividing, there is great metabolic activity, the cell grows and duplicates its genetic material, preparing for cell division. It consists of three phases:  

  • Phase G1. After the cell has divided, the G 1 phase  is a stage of cell growth and duplication of organelles and cytoplasmic structures.

In the G1 phase, as in the rest of the interphasefacetranscription and translation (protein synthesis) take place. It is the most variable period of the cell cycle. DNA synthesis does not occur.  

In the G1 phase, the cell has intense biochemical activity, increases its size and duplicates its enzymesribosomesmitochondria and other molecules and cytoplasmic structures. The organelles and membranous structures such as the Golgi apparatuskaryothecalysosomes, ... come from the endoplasmic reticulum. Others, such as mitochondria and plastids, will be created from other pre-existing ones.

During the G1 phase, some cells become blocked, stop dividing and enter the G0 phase, in which they undergo a series of transformations that lead to cell differentiation. The cell specializes and expresses the genes that allow it to develop its activity in a tissue. Cells that are in the G0 phase for their entire lives are in a state of rest or quiescence. In some cases, such as neurons and red blood cells, they are so specialized that they have lost their ability to divide cells.

There is a restriction point (R point) or point of no return, at the end of G1, in which the cell that has reached this point, has to follow the S, G2 and M phases .

  • If the cell is of adequate size, has nutrients and reproduction is necessary, it will go into the S phase.
  • If nutrients are lacking or contact inhibition occurs, the cell does not divide and will not enter the S phase.

Sometimes a cell escapes the normal controls of cell division and death. When that cell begins to proliferate, reproducing in an uncontrolled way, the pathology of cancer begins. This overgrowth can lead to the formation of a mass of cells called a tumor.

If a cancer cell can stay in G0 phase, without further dividing, it will have achieved a great triumph against cancer.

  • S phase  (S of DNA synthesis). After the cell has increased in size by G1, the cell has to continue preparing for cell division. In this phase, it duplicates its genetic material, so that each daughter cell has an identical copy of the cell's chromosomes (sister chromatids linked by a centromere). In addition to DNA replication, the synthesis of histone proteins and other chromosomal proteins also occurs, which bind to the newly formed DNA. 

In the S phase, the two centrioles also double. The two centrioles separate and a child centriole grows perpendicular to it.

During the synthesis phase, the number of chromosomes does not increase. DNA replicates (duplicates) and each chromosome has two identical chromatids (sister chromatids) so that the chromosomes are double, but the number does not change.

  • Phase G2It begins when DNA synthesis ends (S Phase) and ends when DNA condenses and chromosomes appear. The RNA necessary to synthesize the proteins involved in mitosis, such as mitotic spindle tubulin, is transcribed and translated.

In this phase, the cell finishes preparing for mitosis. It has twice as much DNA as G1, so it is ready to divide. If the cell has correctly replicated DNA and the cell size is adequate, the cell will go into M phase.

As cells that are in the G1 phase have half the DNA of those in the G2 phase, we can know what phase the cell is in, just by knowing the amount of DNA.

When the interphaseface is over, the M stage will begin, where the cells will divide and divide their genetic (mitosis) and cytoplasmic (cytokinesis) material between the two daughter cells. Then phase G1 would begin again.

During the G0, G1, S and G2 phases, the cell nucleus is called the interphasephase nucleus, but during the M phase the nucleus disintegrates, and the chromosomes become visible.

The number of divisions of a cell is limited, since it is necessary for the correct functioning of the organism. This is called apoptosis or programmed cell death. When it takes about 50 divisions, the cell enters the G0 phase, in a state of senescence. Later, programmed cell death or apoptosis will arrive.

The senescence and apoptosis are necessary for the body to function properly.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Aragon. June 2007, option A. Question 3 .- (2 points).

Answer the following questions: What is a chromosome? How is it related to chromatin? What is the reason for talking about "sister" chromatids? When do sister chromatids form? Is there a situation where sister chromatids can be different?

Castilla y León, July 2018, option B, question 2.

In relation to the cell cycle:

a) At what stage of the cell cycle does the G2 phase take place? What is the fundamental process that occurs in the G2 phase? What is the DNA content for a diploid cell in G2 phase? (0.75)

b) Indicate the differences between the different types of chromatin that can be found in interphase. (0.5)

c) In what phase of meiosis does chiasm formation and gene recombination take place? State the difference between anaphase I and II of meiosis. (0.5)

Madrid, June 2016, option B, question 3.

Regarding the cell cycle in an animal cell:

a) Explain the variation in the amount of DNA in a somatic cell throughout the cell cycle (1 point).
b) Define haploid and diploid cells (0.5 points).
c) Explain what the G0 phase of the cell cycle consists of (0.5 points).

Valencian Community, July 2019, option B, block 3, question 6

A cell in interphase (G1 period) has a total content of nuclear DNA of 4 x 10 -6 g, distributed in 6 chromatids:

a) What will be the DNA content in the G2 stage of its cycle? Reason for the answer;

b) How many chromatids will it have in stage G2? Give reasons for the answer (2 marks).

Navarra, June 2020, option A, option A, question 4

A cell spends most of its time in interphase.

a) Explain the three stages that can be distinguished in this phase.

b) Explain what happens if the cell enters phase G0 .

Fundamental ideas about the interphace

The interphace

  • It is the longest stage of the cell cycle.
  • It has three phases:
    • Phase G1.
      • Cell growth.
      • Organelle duplication.
      • Some enter phase G0:
        • State of rest or quiescence.
        • Cell differentiation.
        • It does not follow the cell cycle.
    • S phase.
    • Phase G2.
      • The cell prepares for cell division.
      • DNA is transcribed and the proteins necessary to form the mitotic spindle and for cell division are formed.
      • The amount of DNA is 4n.