# Confusion about the duration of different phases of the cell cycle such as G1, G2 & S

We all know that normally most of our cells (which are alive and have nuclei - except for cells such as "stem cells", "red blood cells", etc) spend most of their lives in interphase.

But the Interphase itself is also composed of other parts, other stages, including G1, S, and G2.

Is the staying duration of the most human cells in each stage(G1,G2 & S) is comparable to the other stage?

For example, is it true to say that:

"Most human cells, which have the ability to divide(passing the cell cycle), spend most of their lives on stage G1 than S phase or vice versa."?

Usually, which stage is the longest or shortest?

It is quite clear that the G1 is normally longer that G2 and as far as I know the G2 is the shortest stage in interphase, but what about G1 and S?

Is stage S usually longer than G1?

Is there any information?

It depends on the conditions, cell type or state of the cell.

I don't think anyone here can do better justice to the question for a beginner than this web page.

To show you why your answer is not answerable, by way of example: some cells exit the cell cycle and enter a stage called G0. This can be a permanent state for some cells, or, for instance, others may return to the cycle if they receive (external) signals.

Here is a very loose approximation, circles are to scale with respect to cycle time. Notice, for instance, the human circle is for an immortalized cell line under laboratory conditions, rather than for cells in your body. A neuron (brain) or an enterocyte (gut) have vastly different cell cycle states, so it's impossible to give you a single straight answer without misleading you totally.

Bonus food for thought: notice that the fraction of time cells spend on G1, S, G2 and mitosis is also different between different cell types.

Bonus food for thought #2: In fruit fly embryos (pictured bottom right in the above picture), you have an extreme example of unconventional (non-textbook) cycling. Rather than synthesizing new cytoplasmic materials, the size of the developing embryo is constant except for the replication of the genetic material. This happens in the growing larva for ~10 cell divisions, in thousands of cells. One of these cycles takes about 8 minutes to complete fully. That's an impressive time to copy a genome; most* bacteria can't do it this quickly!

(*any that I am aware of)

• Is it true to say "Most human cells, which have the ability to divide(passing the cell cycle), spend most of their lives on stage G1 than S phase or vice versa."? Is there any information?
– a.RR
Jan 21 '19 at 17:56
• I don't think this is known definitively. We can only guess. Most cells are in interphase (i.e. not mitosis+cytokinesis). There is an important cell-cycle checkpoint at the end of G1 which, when passed, means that the cell is preparing for eventual division (S or synthesis phase means it's duplicating its genome). I would hazard to guess most cells in the body, by sheer number, are in G1 or have entered (semi)permanently into the G0 phase. Even some adult stem cells await signals to enter the cell cycle again and divide, and these are the most proliferative cells. Don't quote me on this.
– S Pr
Jan 22 '19 at 14:20
• I wonder whether entering the G0 is only done through G1. Is it possible for the cell to go from stage S or G2 to step G0?
– a.RR
Jan 25 '19 at 9:42
• By definition G0 is prior to S phase. Cells can remain for a long time in G2 but if they are not 'actively readying for division', they are either in G1 or out of the cell cycle entirely, in G0.
– S Pr
Jan 25 '19 at 13:08
• @AmirhoseinRiazi also have a look at biology.stackexchange.com/q/13703/3340 Feb 5 '19 at 15:31

A typical eukaryotic cell cycle is illustrated by human cells in culture. These cells divide once in approximately every 24 hours (Figure 10.1). However, this duration of cell cycle can vary from organism to organism and also from cell type to cell type. Yeast for example, can progress through the cell cycle in only about 90 minutes. The cell cycle is divided into two basic phases: Interphase M Phase (Mitosis phase) The M Phase represents the phase when the actual cell division or mitosis occurs and the interphase represents the phase between two successive M phases. It is significant to note that in the 24 hour average duration of cell cycle of a human cell, cell division proper lasts for only about an hour. The interphase lasts more than 95% of the duration of cell cycle. The M Phase starts with the nuclear division, corresponding to the separation of daughter chromosomes (karyokinesis) and usually ends with division of cytoplasm (cytokinesis). The interphase, though called the resting phase, is the time during which the cell is preparing for division by undergoing both cell growth and DNA replication in an orderly manner.

The interphase is divided into three further phases: G1 phase (Gap 1) S phase (Synthesis) G2 phase (Gap 2)

G1 phase corresponds to the interval between mitosis and initiationof DNA replication. During G1 phase the cell is metabolically active and continuously grows but does not replicate its DNA. S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. However, there is no increase in the chromosome number; if the cell had diploid or 2n number of chromosomes at G1, even after S phase the number of chromosomes remains the same, i.e., 2n.

In animal cells, during the S phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase, proteins are synthesised in preparation for mitosis while cell growth continues.