From Regina Bailey,
Your Guide to Biology.
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• Overview
  
• Mitosis Image Gallery
  
• Glossary of Terms
  
• Quiz

Before a dividing cell enters mitosis, it undergoes a period of growth called interphase. Some 90 percent of a cell's time in the normal cellular cycle may be spent in interphase.

View image of a cell in interphase.

Stages of Interphase

• G1 phase: The period prior to the synthesis of DNA. In this phase, the cell increases in mass in preparation for cell division. Note that the G in G1 represents gap and the 1 represents first, so the G1 phase is the first gap phase.


• S phase: The period during which DNA is synthesized. In most cells, there is a narrow window of time during which DNA is synthesized. Note that the S represents synthesis.


• G2 phase: The period after DNA synthesis has occurred but prior to the start of prophase. The cell synthesizes proteins and continues to increase in size. Note that the G in G2 represents gap and the 2 represents second, so the G2 phase is the second gap phase.


• In the latter part of interphase, the cell still has nucleoli present.


• The nucleus is bounded by a nuclear envelope and the cell's chromosomes have duplicated but are in the form of chromatin.


• In animal cells, two pair of centrioles formed from the replication of one pair are located outside of the nucleus.