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By the end of this section, you will be able to:
  • Describe the three stages of interphase
  • Discuss the behavior of chromosomes during mitosis and how the cytoplasmic content divides during cytokinesis
  • Define the quiescent G 0 phase
  • Explain how the three internal control checkpoints occur at the end of G 1 , at the G 2 –M transition, and during metaphase

The cell cycle    is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produce two genetically identical cells. The cell cycle has two major phases: interphase and the mitotic phase ( [link] ). During interphase    , the cell grows and DNA is replicated. During the mitotic phase , the replicated DNA and cytoplasmic contents are separated and the cell divides. Watch this video about the cell cycle: (External Link)

This illustration shows the cell cycle, which consists of interphase and the mitotic phase. Interphase is subdivided into G1, S, and G2 phases. Cell growth occurs during G1 and G2, and DNA synthesis occurs during S. The mitotic phase consists of mitosis, in which the nuclear chromatin is divided, and cytokinesis, in which the cytoplasm is divided resulting in two daughter cells.
A cell moves through a series of phases in an orderly manner. During interphase, G 1 involves cell growth and protein synthesis, the S phase involves DNA replication and the replication of the centrosome, and G 2 involves further growth and protein synthesis. The mitotic phase follows interphase. Mitosis is nuclear division during which duplicated chromosomes are segregated and distributed into daughter nuclei. Usually the cell will divide after mitosis in a process called cytokinesis in which the cytoplasm is divided and two daughter cells are formed.

Interphase

During interphase, the cell undergoes normal processes while also preparing for cell division. For a cell to move from interphase to the mitotic phase, many internal and external conditions must be met. The three stages of interphase are called G 1 , S, and G 2 .

G 1 Phase

The first stage of interphase is called the G 1 phase    , or first gap, because little change is visible. However, during the G 1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins, as well as accumulating enough energy reserves to complete the task of replicating each chromosome in the nucleus.

S phase

Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In the S phase    (synthesis phase), DNA replication results in the formation of two identical copies of each chromosome—sister chromatids—that are firmly attached at the centromere region. At this stage, each chromosome is made of two sister chromatids and is a duplicated chromosome. The centrosome is duplicated during the S phase. The two centrosomes will give rise to the mitotic spindle , the apparatus that orchestrates the movement of chromosomes during mitosis. The centrosome consists of a pair of rod-like centrioles at right angles to each other. Centrioles help organize cell division. Centrioles are not present in the centrosomes of many eukaryotic species, such as plants and most fungi.

G 2 Phase

In the G 2 phase    , or second gap, the cell replenishes its energy stores and synthesizes the proteins necessary for chromosome manipulation. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic spindle. There may be additional cell growth during G 2 . The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis.

Questions & Answers

a perfect square v²+2v+_
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algebra 2 Inequalities:If equation 2 = 0 it is an open set?
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or infinite solutions?
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y=10×
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Kristine 2*2*2=8
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Differences Between Laspeyres and Paasche Indices
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J, combine like terms 7x-4y
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f(n)= 2n + 1
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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Source:  OpenStax, Ucd bis2a intro to biology v1.2. OpenStax CNX. Sep 22, 2015 Download for free at https://legacy.cnx.org/content/col11890/1.1
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