Phases of Mitosis: Videos & Practice Problems

Mitosis is a crucial asexual process involving the division of a diploid somatic cell's nucleus, resulting in two genetically identical diploid daughter cells. It consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase. Key events include chromatin condensation, nuclear envelope breakdown, chromosome alignment at the metaphase plate, sister chromatid separation, and reformation of the nuclear envelope. Understanding these phases is essential for grasping cellular reproduction and genetic continuity.

Phases of Mitosis

Mitosis is a crucial asexual process that involves the division of a single parent cell, specifically a somatic cell, which is a body cell that does not contribute to the genetic material passed to the next generation. This process begins with one diploid cell, which contains two copies of each chromosome, and results in two genetically identical diploid cells. The key characteristic of mitosis is that it maintains the diploid state throughout the process, distinguishing it from meiosis, which will be covered later.

Mitosis consists of five distinct phases: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase, the chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down. In prometaphase, the nuclear envelope is completely gone, and spindle fibers attach to the chromosomes. Metaphase is characterized by the alignment of chromosomes along the metaphase plate. Anaphase follows, where sister chromatids are pulled apart to opposite poles of the cell. Finally, telophase sees the reformation of the nuclear envelope around the separated sets of chromosomes, resulting in two nuclei within a single cell.

It is important to note that mitosis is defined as the division of the nucleus and the genetic material, culminating in a cell that still appears connected but contains two nuclei. This division is subsequently followed by cytokinesis, the process that divides the cytoplasm, ultimately leading to the formation of two separate daughter cells, each with its own nucleus.

Understanding these phases and their significance is essential for grasping the overall process of cell division and its role in growth, repair, and asexual reproduction in multicellular organisms.

How to Remember the Order of the Phases of Mitosis

Mitosis is a crucial process of cell division that consists of five distinct phases: prophase, prometaphase, metaphase, anaphase, and telophase. To effectively remember the order of these phases, a mnemonic strategy can be employed.

Start with metaphase, which is the central phase of mitosis. The letter M in metaphase can be associated with the word middle, indicating its position in the sequence. Since there are five phases in total, metaphase is flanked by two phases before it and two phases after it.

The phases preceding metaphase are prometaphase and prophase. The prefix pro in both terms signifies before, helping to establish their order. Prophase is the initial phase of mitosis, occurring first, while prometaphase follows prophase and comes just before metaphase.

After metaphase, the next phase is anaphase. The letter A in anaphase can be linked to the word after, indicating that it occurs right after metaphase.

Finally, the last phase is telophase, which can be remembered by the letter T representing tail end, as it concludes the process of mitosis.

By associating each phase with its respective mnemonic, one can easily recall the order of mitosis: prophase, prometaphase, metaphase, anaphase, and telophase. This understanding will aid in mastering the concepts of cell division as you progress in your studies.

The correct sequence for the phases of mitosis is:

• A. a) Prophase - prometaphase - anaphase - metaphase – telophase.
• B. b) Prophase - prometaphase - metaphase - anaphase – telophase.
• C. c) Prometaphase - prophase - metaphase - anaphase – telophase.
• D. d) Metaphase - anaphase - interphase - prophase – telophase

Answer: (B)

Prophase

The first phase of mitosis is known as prophase, during which several critical events unfold. Initially, the loosely coiled chromatin, which is the form of DNA present during interphase, condenses into distinct chromosomes. Each chromosome consists of two sister chromatids that are connected at a region called the centromere. It is important to differentiate the centromere from the centrosome; the centromere is the constricted area of the chromosome where sister chromatids are linked, while the centrosome is the structure responsible for forming the mitotic spindle.

As prophase progresses, the nucleolus, a key site for ribosome synthesis located within the nucleus, disappears. This disappearance signifies a halt in ribosome production, indicating that the cell is preparing for division. Additionally, the two centrosomes migrate to opposite poles of the cell, initiating the formation of the mitotic spindle. The mitotic spindle is composed of microtubule proteins that play a crucial role in the movement of chromosomes during mitosis.

In summary, during prophase, chromatin condenses into distinct chromosomes, the nucleolus disappears, and the centrosomes move to opposite poles to form the mitotic spindle. These events set the stage for the subsequent phase of mitosis, known as prometaphase, where further preparations for chromosome separation will occur.

Prometaphase

After prophase, the next stage of mitosis is prometaphase, which is sometimes referred to as late prophase in various textbooks. This terminology can lead to some confusion, as some resources may not distinguish prometaphase as a separate phase, instead combining its events with prophase. Understanding this distinction is crucial for clarity in studying mitosis.

During prometaphase, two significant events occur. First, the nuclear envelope degrades, exposing the chromosomes to the cytoplasm. This breakdown is essential as it allows the mitotic spindle, which has been forming, to connect to the chromosomes. The connection occurs through specific proteins known as kinetochore proteins, located at the centromere of each chromosome. The centromere is the constricted region where the two sister chromatids meet, and it plays a vital role in chromosome movement.

As the nuclear envelope disintegrates, the chromosomes become accessible, enabling the microtubules of the mitotic spindle to attach to the kinetochores. This attachment is crucial for the subsequent movement of chromosomes during the next phase of mitosis. The kinetochore proteins serve as anchor points for the spindle fibers, facilitating the proper alignment and separation of chromosomes as the cell prepares to divide.

In summary, prometaphase is characterized by the degradation of the nuclear envelope and the attachment of the mitotic spindle to the chromosomes via kinetochore proteins, setting the stage for the orderly distribution of genetic material in the following metaphase.

The phase of mitosis where chromosomes condense and centrosomes move to opposite poles of the cell is:

• A. Prometaphase
• B. Metaphase
• C. Prophase
• D. Anaphase
• E. Telophase

Answer: (C)

Why does the nuclear envelope break down during prometaphase?

• A. To allow the chromosomes to condense.
• B. To allow the sister chromatids to form
• C. To allow the mitotic spindle to form.
• D. To allow spindle fibers to attach to chromosomes.

Answer: (D)

Metaphase

Metaphase is the third phase of mitosis, characterized by the alignment of chromosomes at the cell's equator, known as the metaphase plate. A helpful mnemonic to remember this phase is the letter "M," which stands for both "metaphase" and "middle." During this stage, mitotic spindles play a crucial role in organizing the chromosomes into a single file line at the center of the cell.

Understanding the arrangement of chromosomes during metaphase is essential, as it differs from the alignment seen in meiosis, where chromosomes may line up in two rows instead of one. This distinction is significant for comprehending the processes of cell division and genetic variation.

As metaphase concludes, the next phase of mitosis is anaphase, where the chromosomes will begin to separate and move toward opposite poles of the cell. This orderly progression through the phases of mitosis ensures accurate distribution of genetic material to the daughter cells.

The mitotic spindle plays a critical role in which of the following processes of cellular division?

• A. Splitting the cytoplasm following mitosis.
• B. Triggering the condensation of chromosomes.
• C. Dissolving the nuclear membrane.
• D. Moving the chromosomes within the cell.

Answer: (D)

Which of the following events characterizes metaphase of mitosis?
I. Movement of chromosomes to the equatorial plane (metaphase plate) of the cell.
II. A spindle fiber attaches to each sister chromatid.
III. Separation of sister chromatids that are being pulled to the poles of the cell.

• A. I.
• B. II.
• C. III.
• D. I and II.
• E. All of these

Answer: (A)

Metaphase is characterized by ________.

• A. Separation of the sister chromatids.
• B. Separation of the cytoplasm.
• C. Alignment of chromosomes along the cell's equator.
• D. Alignment of the mitotic spindle along the cell's equator.

Answer: (C)

Anaphase

The fourth phase of mitosis is known as anaphase, a term that can be easily remembered by associating the letter "a" in anaphase with the word "apart." During this critical stage, sister chromatids are pulled apart towards opposite ends of the cell, ensuring that each daughter cell receives an identical copy of the DNA. This separation is facilitated by the mitotic spindle, which plays a crucial role in the movement of chromatids.

In anaphase, some components of the mitotic spindle shorten, effectively pulling the chromatids apart. Simultaneously, other parts of the spindle lengthen, which stretches the cell and aids in the overall division process. This dual action of the spindle is essential for the proper distribution of genetic material.

To visualize this process, consider the previous phase, metaphase, where replicated chromosomes are aligned at the metaphase plate. As anaphase progresses, these sister chromatids begin to move away from each other, with one chromatid being pulled in one direction and its partner in the opposite direction. This movement is crucial for ensuring that each new cell will have the correct number of chromosomes.

In summary, anaphase is characterized by the separation of sister chromatids, facilitated by the dynamic actions of the mitotic spindle, which both shortens and lengthens to ensure effective cell division. The next phase, telophase, will further elaborate on the concluding steps of mitosis.

In what way do kinetochore microtubules facilitate the process of splitting the sister chromatids?

• A. They use motor proteins to hydrolyze the centromere at specific arginine residues.
• B. They create tension by pulling toward opposite poles.
• C. They slide past each other like actin microfilaments.
• D. They phosphorylate the centromere, thereby changing its conformation.

Answer: (B)

Which of the following is a function of the non-kinetochore microtubules?

• A. Maintaining an appropriate spacing among the moving chromosomes.
• B. Starting the separation of the cytoplasm once the final stage of mitosis is complete.
• C. Providing the ATP needed by the kinetochore microtubules to move the chromosomes.
• D. Pulling the poles of the cell closer together.
• E. Pushing the poles of the cell further apart.

Answer: (E)

Telophase

Telophase is the fifth and final phase of mitosis, often remembered as the "tail end" of the process. This phase is essentially the reverse of prophase and prometaphase, making it easier to understand if you recall those earlier stages. During telophase, the tightly coiled chromosomes begin to unwind back into their loosely coiled chromatin state, marking a significant transition in the cell division process.

In prophase and prometaphase, the mitotic spindle forms to help separate the chromosomes. However, in telophase, this spindle structure degrades, indicating the end of its role in mitosis. Additionally, while the nucleolus and nuclear envelope disappear during the earlier phases, they reappear in telophase. This reformation occurs at each end of the cell, resulting in the creation of two distinct nuclei.

To summarize the key events of telophase: the chromosomes unwind into chromatin, the nucleolus reforms, the nuclear envelope reestablishes itself, and the mitotic spindle breaks down. By the end of telophase, the cell has successfully divided its genetic material, preparing for the final steps of cell division. Understanding these processes is crucial for grasping how cells replicate and maintain genetic integrity.

The nuclear envelopes form and the mitotic spindles disassembles during telophase in preparation for what?

• A. The merging of the two nuclei.
• B. The division of the cell into two daughter cells, each with their own nuclei.
• C. The division of the cell into four daughter cells, each with half a nuclei.
• D. Nothing, the cell now possesses two nuclei and twice the amount of genetic material.

Answer: (B)

The circles labeled A to E each represent the chromosomes within a cell during a single phase of mitosis. Which image is showing one of the newly created nuclei at the end of telophase?

• A. A
• B. B
• C. C
• D. D
• E. E

Answer: (D)

At which phase of the cell cycle do centrosomes begin to move apart in animal cells?

• A. Anaphase
• B. Metaphase
• C. Telophase
• D. Prophase

Answer: (D)

Scientists isolate cells in various phases of the cell cycle. They isolate a group of cells that have 1 1/2 times more DNA than G1 phase cells. What is the most likely part of the cell cycle from which these cells were isolated?

• A. between the G1 and S phases in the cell cycle.
• B. in the G2 phase of the cell cycle.
• C. in the M phase of the cell cycle.
• D. in the S phase of the cell cycle.

Answer: (D)

If there are 40 centromeres in a cell at anaphase of mitosis, how many chromosomes will be found in each daughter cell following cytokinesis?

• A. 10.
• B. 20.
• C. 40.
• D. 80.

Answer: (B)

Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol prevents microtubule depolymerization (breaking down). Thus, Taxol stops mitosis by interfering with which of the following structures or processes?

• A. The mitotic spindle.
• B. Cytokinesis.
• C. DNA replication.
• D. Chromosome condensation.

Answer: (A)

Here’s what students ask on this topic:

What are the phases of mitosis and their key events?

Mitosis consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase. In prophase, chromatin condenses into distinct chromosomes, the nucleolus disappears, and the mitotic spindle begins to form. During prometaphase, the nuclear envelope breaks down, exposing chromosomes to the cytoplasm, and the mitotic spindle attaches to kinetochores. In metaphase, chromosomes align at the cell's equator, forming the metaphase plate. Anaphase involves the separation of sister chromatids to opposite poles of the cell. Finally, in telophase, chromosomes decondense back into chromatin, the nuclear envelope and nucleolus reform, and the mitotic spindle disassembles, resulting in two nuclei.

How can you remember the order of the phases of mitosis?

To remember the order of the phases of mitosis, you can use mnemonic devices. For example, think of the M in metaphase as the M in the word 'middle,' indicating it is the middle phase. Prophase and prometaphase come before metaphase, with 'pro' meaning 'before.' Anaphase follows metaphase, with the A in anaphase representing 'after.' Telophase is the final phase, with the T in telophase standing for 'tail end.' This mnemonic helps recall the sequence: prophase, prometaphase, metaphase, anaphase, and telophase.

What happens during prophase in mitosis?

During prophase, several key events occur: the chromatin condenses into distinct chromosomes, each consisting of sister chromatids joined at the centromere. The nucleolus, responsible for ribosome synthesis, disappears, halting ribosome production. Additionally, the centrosomes, which form the mitotic spindle, migrate to opposite poles of the cell. The mitotic spindle, composed of microtubules, begins to form, preparing to move the chromosomes during subsequent phases of mitosis.

What is the significance of metaphase in mitosis?

Metaphase is significant because it ensures that chromosomes are properly aligned at the cell's equator, forming the metaphase plate. This alignment is crucial for the accurate separation of sister chromatids during anaphase. The mitotic spindle attaches to the kinetochores of the chromosomes, ensuring that each daughter cell will receive an identical set of chromosomes. Proper alignment and attachment prevent errors in chromosome distribution, which could lead to genetic abnormalities in the daughter cells.

How does telophase differ from prophase in mitosis?

Telophase is essentially the reverse of prophase. During prophase, chromatin condenses into tightly coiled chromosomes, the nucleolus disappears, and the mitotic spindle forms. In contrast, during telophase, the tightly coiled chromosomes begin to unwind back into chromatin, the nucleolus reappears, and the nuclear envelope reforms around each set of chromosomes, resulting in two distinct nuclei. Additionally, the mitotic spindle disassembles in telophase, completing the process of nuclear division.