As expected, we found that G1 showed the most variability among cell types, ranging from 2.1 h in H9 to 7.9 h in RPE. In contrast, the durations of S (7.6–10.1 h), G2 (3.4–4.0 h), and M (~ 0.5 h) were relatively consistent (Fig 1B).

The G1 phase stands for gap 1 and is when organelles replicate and the cell grows. The S phase stands for synthesis and is when DNA is replicated. The G2 phase stands for gap 2 and is when DNA is proofread and DNA damage is repaired.

The DNA is copied. The chromosome now consists of two sister chromatids, which are connected by proteins called cohesins. The chromosome condenses. It is still made up of two sister chromatids, but they are now short and compact rather than long and stringy.

Interphase is the longest part of the cell cycle. This is when the cell grows and copies its DNA before moving into mitosis.

The stage most variable in duration is G1. In less favorable growth conditions when the cell cycle duration increases this is the stage that is mostly affected, probably due to the time it takes until some regulatory size checkpoint is reached.

Cells typically spend far more time in interphase than they do in mitosis. Of the four phases, G1 is most variable in terms of duration, although it is often the longest portion of the cell cycle (Figure 1).

Chapter 5 - The Cell Introduction. All living things are composed of small units of life called cells. Cells are complex active and reproducing units of life. The concept that cells are the basic unit of life is known as the cell theory. There are two basic groups of cells.