Interphase - Online Tutor, Practice Problems & Exam Prep

Interphase is the longest phase of the cell cycle, consisting of four subphases: G1, S, G2, and G0. In G1, cells grow and perform normal functions. The S phase involves DNA replication, producing replicated chromosomes and centrosomes, essential for mitosis. G2 continues cell growth and prepares for division. The G0 phase is a non-dividing state where cells may remain temporarily or permanently. Centrosomes organize the mitotic spindle, crucial for chromosome separation during mitosis, highlighting the importance of these structures in cellular division.

Interphase

So now that we briefly introduced the cell cycle in our previous lesson videos, in this video, we're going to begin to discuss the first major phase of the cell cycle, which is interphase. Recall from our previous lesson videos that interphase is a non-dividing stage where the cell is not going to be dividing. Instead, interphase is a stage of cell growth and organelle and enzyme production in preparation for cell division. Interphase typically makes up the vast majority of the cell cycle, and that's because interphase takes quite a long time with respect to the M phase, which is a relatively short period of time because it's a relatively fast process. The dividing phase occurs relatively quickly in comparison to interphase, which takes a long time.

Once again, in this video, we are focusing mainly on interphase, the phase that makes up the majority of the cell cycle and takes a long time. Recall from our previous lesson videos that within interphase there are smaller subphases. The subphases of interphase include four subphases. These four subphases are based on specific events that occur inside the cell. The very first subphase here we have is G₁.

In G₁, the 'G' stands for growth. This is because, in the G₁ subphase of interphase, the cell is going to be performing its normal functions. If it's a heart cell, it's going to be doing whatever a heart cell does. If it's a liver cell, it's going to be doing whatever a liver cell does, and so on. In the G₁ subphase of interphase, the cell is going to be performing its normal functions. In addition, it's also going to be growing and producing organelles, enzymes, and proteins.

Then, note that after the G₁ phase, we're actually going to skip over the G₀ phase for now, and we're going to transition straight from the G₁ to the S phase. The 'S' is symbolic for the 'S' in synthesis. This represents DNA synthesis or DNA replication, and that's exactly what the S phase is characterized by. The DNA is going to be synthesized or replicated, producing a replicated chromosome with two sister chromatids. Also, a cytoplasmic protein called the centrosome, not to be confused with the centromere or the waist position of a replicated chromosome, will be replicated during the S phase as well. So it's also replicated during the S phase, in addition to the DNA. You can see, in this image of the S phase, it's characterized mainly by DNA replication, but in addition to DNA replication, a structure called the centrosome is also going to be replicated.

Then, what follows the S phase is the G₂ phase. G₂ also stands for growth. Really, it's just a continuation of G₁ in a way because the cell is going to continue to grow and produce new proteins. And, because G₂ is the last phase just before the M phase, G₂ is also going to be preparing for the M phase. So, it's going to be creating new proteins that are required for the M phase, essentially prepping and preparing itself for the phase that follows. What you'll notice here in this image is that, at the end of the G₂ phase or in the G₂ phase, the cell is going to continue to grow, so it's characterized by cell growth. And also, preparation for the division, essentially preparing itself for the M phase.

The only phase that we have not yet talked about is this G₀ phase, which is a non-dividing phase where the cell is not dividing. Essentially, a cell would go from initially starting in the G₁ phase, but it would only transition into the S phase, DNA replication, if the cell is going to commit to dividing. But if the cell does not want to commit to dividing, then it will not go into the S phase. Instead, if the cell does not want to commit to dividing, then the cell would go into the G₀ phase. G₀ is a non-dividing phase where cells are not going to replicate their DNA nor are they going to prepare for cell division. G₀ is basically a phase where cells will not divide. It will not continue through the cell cycle as normal. Some cells will be in the G₀ phase for a permanent period of time, whereas other cells will enter the G₀ phase for a temporary period of time and then they can also return back to the G₁ phase and then continue to divide.

This concludes our introduction to interphase and the subphases of interphase, and we'll be able to get practice applying these concepts and breaking down this image here as we move forward in our course. So, I'll see you all in our next video.

Cells spend the majority of their time in which one of the following phases of the cell cycle?

• A. Interphase.
• B. Prometaphase.
• C. Metaphase.
• D. Anaphase.

The first phase in the cell cycle (G1) corresponds to ___________.

• A. The phase between DNA replication and the M phase.
• B. The beginning of mitosis.
• C. The phase in which DNA is being replicated.
• D. Normal growth and cell function.

Which pair includes a phase of the cell cycle and a cellular process that occurs during that phase?

• A. G1 phase, DNA replication.
• B. G2 phase, preparation for mitosis.
• C. S phase, cell division.
• D. M phase, cell growth.

Centrosomes & Mitotic Spindles

In this video, we're going to briefly introduce centrosomes and mitotic spindles. Recall from our last lesson video that during the S subphase of interphase, it's characterized by DNA synthesis where the cell's going to replicate their DNA, but they also replicate another structure called the centrosome. The centrosome is not to be confused with the centromere, which again is the waist position of a replicated chromosome where the two sister chromatids come together. The centrosome is different than the centromere. The centrosome is a cytoplasmic protein complex that forms or organizes what are known as the mitotic spindle.

And the mitotic spindle is very very important for mitosis, which occurs, of course during the M phase of the cell cycle. The mitotic spindle is really just microtubule proteins of the cytoskeleton that coordinates division of the chromosomes, essentially dividing the DNA into the two daughter cells. Here what we're seeing is that in our example image is that the centrosome is going to be replicated in the S phase and the centrosome is ultimately going to be responsible for forming the mitotic spindle during mitosis. Over here in this image down below, notice over here on the left we're showing you a single cell that has only one centrosome. Notice that a single centrosome actually consists of these two smaller proteins here, and so we have one single centrosome right here.

And, we have the nucleus of the cell and within the nucleus we have these unreplicated chromosomes. Notice that, after the S phase, remember the S phase is the subphase of interphase where DNA synthesis is going to occur, DNA replication. But in addition to DNA replication, the centrosome is also going to be replicated. Notice that the centrosome is replicated. Now there are two centrosomes. There was one over here and now there's a second centrosome over here. We have these centrosomes here, but also in addition to the centrosomes being replicated, of course, the DNA is going to also be replicated. So we convert the unreplicated chromosomes here into replicated chromosomes. Notice they each, we have this, these X-shaped chromosomes here indicating that they are replicated, whereas over here they are not X-shaped, they are more linear like what you see here. And so really that is the main point here, and, ultimately these centrosomes, again, are going to be very important during mitosis because during mitosis, they are going to form what are known as the mitotic spindle.

Here you can see the mitotic spindle are these structures that are projecting off of the centrosome and they are forming these microtubules that are going to be important for ultimately moving the DNA around and splitting the division of the chromosomes, dividing the chromosomes. Again, this will make, the centrosomes and the mitotic spindle are going to be more relevant once we start talking about mitosis a little bit later in our course. So this is a little bit of foreshadowing here for what you are going to see as we move forward. This here concludes our brief introduction to centrosomes and the mitotic spindles, and we'll be able to get some practice as we move forward in our course. So I'll see you all in our next video.

What is the name of the microtubule-organizing center found in animal cells as an identifiable structure present during all phases of the cell cycle?

• A. Spindle.
• B. Centromere.
• C. Centrosome.
• D. Kinetochore.

What is the role of the spindle fibers during mitosis?

• A. They separate the chromosomes.
• B. They break down the nuclear envelope.
• C. They replicate the DNA.
• D. They condense the chromosomes.

Here’s what students ask on this topic:

What is interphase and why is it important in the cell cycle?

Interphase is the longest phase of the cell cycle, during which the cell grows, performs its normal functions, and prepares for division. It consists of four subphases: G1, S, G2, and G0. In G1, the cell grows and produces organelles and proteins. The S phase involves DNA replication, producing replicated chromosomes and centrosomes. G2 continues cell growth and prepares for mitosis. The G0 phase is a non-dividing state where cells may remain temporarily or permanently. Interphase is crucial because it ensures that the cell is adequately prepared for division, with all necessary components duplicated and ready for mitosis.

What happens during the G1 phase of interphase?

During the G1 phase of interphase, the cell grows and performs its normal functions. This phase is characterized by the production of organelles, enzymes, and proteins necessary for the cell's activities. If the cell is a heart cell, it will perform functions specific to heart cells; if it is a liver cell, it will perform liver-specific functions. Additionally, the cell increases in size and prepares for DNA replication, which occurs in the subsequent S phase. The G1 phase is essential for ensuring that the cell is ready for the next steps in the cell cycle.

What is the significance of the S phase in interphase?

The S phase, or synthesis phase, is crucial in interphase because it is when DNA replication occurs. During this phase, the cell's DNA is duplicated, resulting in replicated chromosomes with two sister chromatids. Additionally, the centrosome, a cytoplasmic protein complex, is also replicated. The centrosome is essential for forming the mitotic spindle during mitosis, which helps in the accurate separation of chromosomes into daughter cells. The S phase ensures that each daughter cell will receive an identical set of chromosomes, which is vital for maintaining genetic consistency.

What is the role of the G2 phase in interphase?

The G2 phase is the final subphase of interphase, where the cell continues to grow and prepares for mitosis. During this phase, the cell produces proteins and other components necessary for cell division. It also checks for any DNA damage that may have occurred during the S phase and ensures that all DNA has been accurately replicated. The G2 phase is essential for ensuring that the cell is fully prepared for the M phase, where mitosis and cytokinesis occur, leading to the formation of two daughter cells.

What is the G0 phase, and how does it differ from other phases of interphase?

The G0 phase is a non-dividing state where cells exit the cell cycle and do not prepare for division. Cells in the G0 phase do not replicate their DNA or produce components necessary for mitosis. Some cells enter the G0 phase temporarily and can return to the G1 phase to resume the cell cycle, while others remain in G0 permanently. This phase is significant for cells that do not need to divide frequently, such as nerve cells and muscle cells. The G0 phase allows cells to perform their specialized functions without the need for division.