Ch 2 Test: Part C - The Cell Cycle and Stages of Mitosis Flashcards
What is interphase, and how long does the cell spend in this phase?
During interphase, the cell is growing and preparing for cell division, (mitosis.) It spends 90% of its time in this phase.
What are the stages/phases of interphase and what occurs in each of them?
First Growth Phase (G1)
This phase is a period of cell growth. During this phase, the cell also produces (duplicates) new proteins and organelles.
Synthesis Phase (S)
During this phase, the cell makes (synthesizes) an entire copy of each of the DNA within cell. Key proteins that are associated with chromosomes are also produced during this phase.
Second Growth Phase (G2)
Once the DNA has been copied, the cell moves into the second growth phase. During this phase, the cell produces the enzymes needed for cell division. It is the shortest of the interphase phases.
What is mitosis phase (M Phase), how many stages/phases does it have, and what are their names?
Once the cell is ready to divide and make two new identical daughter cells, it enters the mitosis phase. There are four stages/phases in mitosis phase (M Phase): prophase, metaphase, anaphase, telophase.
What occurs in prophase?
During prophase, the chromatin (DNA and proteins) that make up the chromosomes condenses. At this stage, the chromosome is two identical copies called sister chromatids attached together at a centromere.
These sister chromatids will eventually separate and move to opposite sides of the cell. To enable this movement, the nuclear structures and nuclear envelope disintegrate.
Additionally, framework called the mitotic spindle which moves chromatids around the cell forms. Chromatids are attached to the spindle at their centromeres. In animal cells, a pair of organelles called centrioles moves to each end of the cell, forming the poles of the mitotic spindle.
What occurs in metaphase?
As the cell moves into the second stage of mitosis, called metaphase, each chromosome becomes completely condensed. The chromosomes move toward the center of the cell and line up in the middle of the cell. The mitotic spindle is complete and is made of tiny tubes that extend from each pole to the middle of the cell. These tubes connect to the centromere of each chromosome at the two poles.
What occurs in anaphase?
During anaphase, the sister chromatids separate at the centromere (the proteins holding them together are dissolved). Each chromatid is now a complete chromosome, and the separated chromosomes are pulled to the opposite ends of the cell, preparing it for final division.
What occurs in telophase?
The mitotic spindle breaks down, two new nuclei form and the chromosomes lose their distinct shape (they become chromatin once more).
What is the cytokinesis phase & what occurs?
Cytokinesis is the process of splitting the cytoplasm into two separate cells. It occurs within the mitosis (M Phase) and is the last process to occur before the process of cell division is complete.
The cell membrane pinches inward (cleavage furrow) in animal cells.
In plant cells, the cell plate forms the cell wall and inner cell membrane in each new cell, before this happens, the parent cell briefly has two nuclei during telophase.
At the end of cytokinesis, the two new cells return to interphase conditions. Two nuclei form where each pole of the parent cell was.
What are checkpoints?
The cell cycle has three checkpoints (regulations) to ensure the cell is ready to go to the next phase.
What are the three checkpoints in the cell cycle and what occurs?
G1 Checkpoint
Occurs near the end of G1 phase.
→ Checks for correct cell size, a sufficient amount of nutrients, DNA damage, are there growth factors (signals cell to begin DNA replication process)
→ If it does not pass through this checkpoint, it may enter G0 (resting state)
→ Some cells, like adult nerve cells are permanently in a resting state (they never do mitosis)
G2 Checkpoint
→ Occurs at the end of G2 (Gap 2) phase.
→ Checks for correct cell size and if DNA was replicated correctly
Spindle Assembly Checkpoint
→ Occurs near the end of the M (Mitosis) phase, during metaphase.
→ Checks if chromosomes are attached to the spindle correctly
What indicators would tell a cell not to enter mitosis?
The following indicators or checkpoints will tell a cell not to enter mitosis:
- Signals from surrounding cells tell the cell not to divide
- There are not enough nutrients to provide for cell growth
- The DNA within the nucleus has not been replicated
- The DNA is damaged
What happens if the checkpoints aren’t followed and what causes a cell to ignore them?
If checkpoints are not followed, the cell will divide uncontrollably and become cancerous. DNA damage may cause a cell to disregard the checkpoints.
