InterphaseThe part of the cycle between divisions. It is made of G1, S and G2. In it the cell grows and prepares to divide.
G1 phase (first gap)Little change is visible, but the cell is busy. It gathers the building blocks for DNA and the energy reserves it needs to copy its chromosomes.
S phase (synthesis)DNA is replicated, making identical pairs of sister chromatids. They are joined at the centromere. The centrosome is duplicated too.
G2 phase (second gap)The cell restores its energy. It makes the proteins it needs to move chromosomes, and finishes its preparations for mitosis.
M phase (mitotic phase)Division itself, giving two identical daughter cells. Mitosis divides the nucleus, then cytokinesis usually divides the cytoplasm.
Mitosis (karyokinesis)Division of the nucleus. The phases are prophase, prometaphase, metaphase, anaphase and telophase.
CytokinesisDivision of the cytoplasm into two daughter cells, usually right after mitosis.
NucleusHolds the DNA. In interphase it is whole, its chromatin spread out.
The cycle: 9 2
G0 phase (resting)A resting state outside the cycle. Cells in it are not preparing to divide. Some enter it for a while. Mature heart muscle and nerve cells stay in it.
CheckpointsPoints where the cycle can be halted until conditions are right. They come near the end of G1 (DNA checked), at G2/M (copying checked) and in metaphase (spindle attachment checked).
A cell in interphase: 6 5
Cell membraneThe boundary of the cell, round the cytoplasm.
CytoplasmEverything inside the cell membrane apart from the nucleus. Cytokinesis divides it in two.
NucleolusA dense body inside the nucleus. It disperses when mitosis begins.
ChromatinDNA and its proteins. Through interphase it stays semi-condensed, so no separate chromosomes are visible yet.
Centrosome (with centrioles)Organizes the spindle for division. In animal cells it holds two centrioles at right angles; it is duplicated in S phase.
How this list was compiled: Read 2026-09-26. OpenStax Biology 2e, section 10.2 The Cell Cycle, https://openstax.org/books/biology-2e/pages/10-2-the-cell-cycle : interphase followed by the mitotic phase; the three stages G1 (first gap), S (synthesis of DNA) and G2 (second gap) and what happens in each; semi-condensed chromatin through interphase; sister chromatids attached at the centromeric region; the centrosome duplicated in S phase and, in animal cells, its pair of centrioles at right angles; karyokinesis (mitosis) in five phases and cytokinesis dividing the cytoplasm; the nucleolus dispersing in prophase; the quiescent G0 phase, entered temporarily or, by mature cardiac muscle and nerve cells, permanently. Section 10.3 Control of the Cell Cycle, https://openstax.org/books/biology-2e/pages/10-3-control-of-the-cell-cycle : the three internal checkpoints near the end of G1, at the G2/M transition and during metaphase, and what each assesses. The slice sizes are schematic, not measured lengths. Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
An interphase cell diagram beside the whole cell cycle: label the phases of the cell cycle on the wheel, then the parts of a cell in interphase. Start with the 8 main parts.
Read the full guide
Reading the wheel
Go clockwise from the top: G1, S and G2 make up interphase, then mitosis and cytokinesis make up the M phase. G0 sits outside the wheel, and the three dark bars are the checkpoints.
What an interphase cell looks like
The nucleus is whole and its chromatin stays loose and semi-condensed, so no separate chromosomes show. The nucleolus is visible, and in S phase the centrosome is copied ready for division.
Remember the order with the letters: Gap, Synthesis, Gap, then Mitosis.
Questions and answers
What are the three stages of interphase?
G1, the first gap, when the cell grows and gathers resources; S, when the DNA is copied; and G2, the second gap, when it prepares for mitosis.
What is the G0 phase?
A resting state outside the cycle, where a cell is not preparing to divide. Some cells enter it for a while; mature heart muscle and nerve cells stay in it.
Where are the cell cycle checkpoints?
Near the end of G1, where the DNA is checked; at the G2/M transition, where the copying is checked; and during metaphase, where the spindle attachment is checked.