Cell Division
Cell division is the process of a single cell turning into two nearly identical copies of itself. To do this, the original cell needs to make copies of all its cellular components, including its DNA. Divvying up other cellular components (like organelles and cytoplasm) between the daughter cells happens at random, but a fair and equal splitting of the genetic material is critical. This is why eukaryotes evolved very complex machinery to ensure that the DNA is split equally between the daughter cells. Here, you will take a journey through the major stages of cell division to explore how a cell is able to accomplish this fundamental task.
Written by Noah Green, HHMI's Janelia Research Campus
Background Image by Dylan T. Burnette; Vanderbilt University; Tennessee, USA
Interphase
Interphase is the “daily life” phase of the cell cycle. Most cells spend most of their time in interphase and only move out of it when cell division (mitosis or meiosis) begins. This phase is also called the metabolic phase because it is when the cell obtains nutrients, grows, and performs all other “normal” functions. Interphase is split into three subphases:
- The G1 phase, when the cell is carrying out all its normal cellular tasks.
- The S phase, when the DNA replicates in preparation for cell division.
- The G2 phase, when the rest of the cell is preparing for the start of cell division.
This video shows a HeLa cell in G1 interphase. The movement you can see of orange fibers is the dynamic processes of the protein actin – a key component of the cytoskeleton. Actin performs many essential functions during interphase and cell division.
Once the cell moves out of interphase and begins the process of cell division, it has entered M phase, which includes all the stages of cell division explored below.
Video by Andy Moore, HHMI's Janelia Research Campus
Prophase
The first stage the cell enters upon progressing from interphase is prophase. Prophase is the stage of cell division when the DNA (orange) begins to condense and the centrosomes (organelles that organize and regulate microtubules during cell division) move to opposite ends of the nucleus.
Image by Andy Moore, HHMI's Janelia Research Campus
Prometaphase
After prophase comes an intermediate but essential step called prometaphase. Prometaphase is the stage of cell division when the DNA (orange) is packed into condensed chromosomes and attached to microtubules (white). The nuclear envelope is disassembled, and the chromosomes can begin moving within the cytoplasm.
Image by Andy Moore, HHMI's Janelia Research Campus
Metaphase
The next step is metaphase. During metaphase, the DNA lines up in the middle of the cell, creating a line of chromosomes in the middle of the cell called the metaphase plate (seen here in orange) and prepares to be pulled apart to opposite ends of the cell along microtubules.
Image by Andy Moore, HHMI's Janelia Research Campus
Anaphase
Once the chromosomes are ready, anaphase begins. During anaphase, equal parts of DNA, in the form of condensed chromatids (a chromatid is one of two identical halves of the replicated chromosome – seen here in orange), are transported to opposite sides of the dividing cell.
Image by Andy Moore, HHMI's Janelia Research Campus
Telophase
Once the DNA (orange) reaches either end of the cell, it enters telophase. During telophase, the nuclear envelope (the membrane of the nucleus) begins to form around the DNA. The DNA begins to unpack from its condensed form and the two cells start to split. Telophase is complete once the cell has completely split, undergoing a process called cytokinesis.
Image by Andy Moore, HHMI's Janelia Research Campus
Cytokinesis
Above, you learned that actin filaments are involved in many cellular processes, including cell division. This is especially true of the process of cytokinesis. Cytokinesis is the process by which the parent cell actually splits into two daughter cells. During cytokinesis, actin filaments form a ring around the center of the dividing cell. Once the DNA has been pulled to each end of the cell, this ring contracts until it pinches off the cell membrane, separating the two daughter cells. In this video, you can see the actin protein labeled in orange. Notice how actin becomes more concentrated (brighter orange) at the point when the two cells split toward the end of the video.
Video by Andy Moore, HHMI's Janelia Research Campus
The full cycle of cell division
This video shows a cell going through the whole process of cell division. The actin protein is depth-coded for color, meaning the actin filaments that are close to the viewer are in warm colors like pink and red, and the actin filaments that are farther from the viewer are in cool colors like green and blue. The DNA packed into the chromosomes can be seen as dark patches lining up at the center of the dividing cell and then moving to each daughter cell.
Cell division is one of the most fundamental processes in all of biology. Single-celled organisms use cell division to reproduce and spread, while multicellular organisms like humans use cell division to grow, heal, and much more. Without this intricate and precise process, life as we know it could not exist.
Video by Dylan Burnette, Vanderbilt University
For suggestions on how to incorporate this journey into your teaching, see our “Implementation Suggestions.”