Cytokinesis - Online Tutor, Practice Problems & Exam Prep

Cytokinesis

In this video, we're going to begin our introduction to cytokinesis. Recall from our previous lesson videos that the M phase of the cell cycle consists of both mitosis and cytokinesis. Already in our previous lesson videos, we've covered the 5 phases of mitosis. Recall that mitosis ends up dividing the nucleus and at the end of mitosis, you still technically have a single cell with 2 nuclei. This means that mitosis needs to be followed up by another process called cytokinesis. Cytokinesis is technically the process that's going to produce 2 identical daughter cells by separating the two nuclei. Cytokinesis can be defined as the division of the cytoplasm, essentially separating one cell into two cells. It turns out that animal and plant cell cytokinesis actually differ in their mechanism. Moving forward, we're going to talk about animal cytokinesis and plant cytokinesis in their own separate videos. I'll see you all in our next video to talk about animal cell cytokinesis.

Animal Cell Cytokinesis

In this video, we're going to introduce animal cell cytokinesis. In animal cells, cytokinesis is characterized by the formation of what's known as a cleavage furrow. A cleavage furrow is really just a small indentation of actin filaments mainly, and some myosin filaments as well, at the center of a dividing cell. This cleavage furrow ultimately results in the pinching of the cytoplasm and the separation of the two cells.

If we take a look at our image down below, on the left-hand side notice, we're showing you a cell right after mitosis, and recall that mitosis technically ends with a single cell that has two nuclei. Notice that we still have a single cell here; this is a cell that is still a single cell because the cytoplasm is still connected here, and notice that there are two nuclei here. What you'll notice is that mitosis technically does not end with two cells. Mitosis needs to be followed by the process of cytokinesis, which is what's going to separate the cytoplasm, essentially separating this single cell to form two cells.

During animal cell cytokinesis, a structure referred to as the cleavage furrow is going to form. The cleavage furrow is just this indentation that you can see forming from the result of these contractile actin microfilaments and myosin filaments that form in the middle, or in the center of the dividing cell. Ultimately, this cleavage furrow is going to continue to pinch off the cytoplasm until the cytoplasm has been divided and the two cells have their own cytoplasm and their own nucleus. These would represent the daughter cells that result.

Technically, telophase, which is the final phase of mitosis, and cytokinesis are going to occur simultaneously, which is why mitosis is so highly linked to creating two daughter cells. But technically, it's the process of mitosis and cytokinesis that leads to the two daughter cells.

This here concludes our introduction to animal cell cytokinesis and how it's characterized by the formation of the cleavage furrow. This is going to be different when we look at plant cell cytokinesis in our next video. So, I'll see you all there.

Cytokinesis Example 1

Alright, so here we have an example problem that's asking why cytokinesis is an important part of cell division. After reading through each of these four answer options down below, there are a few that we can eliminate right off the bat. Taking a look at option D below, it says that cytokinesis is responsible for the growth and production of new organelles and other cytoplasmic contents. However, this is not the role of cytokinesis; option D is actually describing the role of interphase. Interphase and cytokinesis are not the same thing, so we can cross off answer option D.

Answer option C states that cytokinesis is responsible for the linking of two sister chromatids, but of course, that is not the case at all - it's not what we've discussed in our previous lesson videos. Now we are between answer options A and B. Notice answer option A claims that cytokinesis is responsible for the proper separation of genetic information. However, it is technically mitosis that is separating the genetic information - the DNA - and splitting the single nucleus to form two nuclei. Therefore, mitosis, not cytokinesis, is responsible for the proper separation of genetic information. Option A is linked more closely to mitosis.

Of course, this leaves answer option B as the correct answer. Cytokinesis is an important part of cell division because it is responsible for the proper separation of cytoplasmic contents, which is exactly how cytokinesis is defined: the division of the cytoplasm. Thus, answer option B is the correct answer for this example problem. That concludes this example, so I'll see you all in our next video.

In animal cell cytokinesis, a cleavage furrow is ________.

• A. A ring of vesicles forming a cell wall.
• B. The equatorial line which chromosomes align along during mitosis.
• C. A groove in the plasma membrane between daughter nuclei.
• D. The space that is created between two chromatids during anaphase.

Plant Cell Cytokinesis

In this video, we're going to introduce plant cell cytokinesis. Plant cell cytokinesis is different from animal cell cytokinesis because, in plant cell cytokinesis, there is no cleavage furrow. It's important to recall from our previous lessons that, unlike animal cells, plant cells are surrounded by a cell wall. In our image below, the cell wall is color-coordinated to this dark green color. It's important to note that in plant cell cytokinesis, no cleavage furrow forms. Instead, vesicles from the Golgi apparatus carry materials to generate what's known as a cell plate. The cell plate is ultimately responsible for helping to separate each of the daughter cells. So instead of a cleavage furrow forming, as happens in animal cells, a cell plate forms in plant cells.

The cell plate is essentially the precursor structure to a fully developed cell wall. The cell plate forms first and eventually develops into a mature cell wall. Looking at our image below, on the far left-hand side, you can see a plant cell with a cell wall undergoing mitosis, specifically in anaphase, where the sister chromatids are being pulled apart. Instead of a cleavage furrow forming in the middle of the cell, Golgi vesicles or vesicles from the Golgi apparatus start to accumulate and form in the middle of the cell. These vesicles carry the materials needed to generate a cell plate. As mitosis continues, a structure referred to as the cell plate forms in the middle of the cell. This cell plate will continue to develop over time into a fully mature cell wall, which we're labeling here.

Once the mature cell wall has formed, the plant cell has successfully undergone a complete cell division. The key takeaway here is that in animal cells, a cleavage furrow forms, but in plant cells, it's the cell plate that forms and eventually develops into a cell wall. This concludes our introduction to plant cell cytokinesis, and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Which of the following are primarily responsible for cytokinesis in plant cells?

• A. Kinetochores.
• B. Golgi-derived vesicles.
• C. Actin and myosin.
• D. Metaphase plate.
• E. Centrosomes.

FtsZ is a bacterial cytoskeletal protein that forms a contractile ring involved in binary fission. Its function is analogous to ________.

• A. the cleavage furrow of eukaryotic animal cells.
• B. the cell plate of eukaryotic plant cells.
• C. the mitotic spindle of eukaryotic cells.
• D. the microtubule-organizing center of eukaryotic cells.