Cell Cycle Flashcards
Which of the following is the correct order of the cell cycle?
B, G1 → S → G2 → M
G1, the first phase of the cell cycle, is where the cell grows in size to prepare for replication. Next, the cell enters S phase, duplicating its DNA.
After DNA replication, the cell progresses through G2 phase, doubling its organelles in preparation for mitosis. Finally, the cell undergoes mitosis in M phase, creating two identical daughter cells.
Key Takeaway:
The correct order of the cell cycle is G1 → S → G2 → M.
During which of the following phases of the cell cycle is a cell in a resting state, performing normal cellular duties?
G0 phase
Cells will spend a large portion of their lives in the G0 phase. In G0, cells are not actively working towards mitosis. Instead, cells in this phase carry out their normal cellular functions.
Key Takeaway:
G0 is the phase during which a cell is not actively preparing for mitosis and is instead carrying out its cellular duties.
Which of the following describes the amount of genetic material in a cell after S phase?
n = number of chromosomes c = number of chromatids
2n4c
Chromosomes (n) are single molecules of DNA that carry the genetic material of an organism. Chromatids (c) are one-half of a duplicated chromosome.
DNA replication occurs during S phase of the cell cycle. Before DNA replication, a cell contains two sets of chromosomes with one copy of each set (2n2c). After DNA replication the cell will still contain two sets of chromosomes, but now with two copies of each set (2n4c).
Key Takeaway:
After DNA replication, the number of chromosomes remains the same, but the number of chromatids has doubled (2n4c).
p53 and Rb tumor suppressor proteins are most active during which of the following?
G1/S checkpoint
The G1/S checkpoint ensures that DNA is intact prior to entering S phase. This step of the cell cycle has a very high activity of tumor suppressor proteins, including retinoblastoma protein (Rb) and p53.
The G1/S checkpoint is very important as it prevents replication of damaged DNA and proliferation of cancerous cells.
Key Takeaway:
Tumor suppressor proteins are very active during the G1/S checkpoint of the cell cycle.
Which of the following binds to E2F to prevent transcription?
Retinoblastoma protein (Rb)
Retinoblastoma protein (Rb) binds to the transcription factor E2F and prevents it from initiating transcription. If a cell passes the G1/S checkpoint, Rb will become phosphorylated by cyclin-dependent kinases and release E2F. E2F will then be free to initiate transcription and the cell will move forward through the cell cycle.
Key Takeaway:
Retinoblastoma protein binds to E2F, preventing DNA transcription until the cell passes the G1/S checkpoint.
Which of the following activates p53?
p53 is activated in response to damaged DNA
p53 is activated in response to damaged DNA found during the G1/S checkpoint. p53 will activate p21, inhibiting cyclin-dependent kinase 4 (CDK4).
With CDK4 inhibited and unable to phosphorylate retinoblastoma (Rb), Rb will remain bound to the transcription factor E2F. While bound by Rb, E2F is unable to initiate transcription, and the cell will become arrested in G1 until the damaged DNA is repaired.
Key Takeaway:
p53 is activated during the G1/S checkpoint by the presence of damaged DNA.
Which of the following occurs at the G1/S checkpoint if irreparable DNA damage is detected?
Release of cytochrome C
If DNA damage is found during the G1/S checkpoint, the cell will enter cell cycle arrest in the G1 phase. If the damage is reparable, the cell will return to the cell cycle after repairs have been made.
If the damage to DNA is irreparable, apoptosis proteins Bax, Bak, and Bad will be activated, leading to the release of cytochrome C from mitochondria. The release of cytochrome C will lead to apoptosis of the cell.
Key Takeaway:
Irreparable DNA damage at the G1/S checkpoint leads to the release of cytochrome C and eventual apoptosis of the cell.
Which is the best description of the two-hit hypothesis?
The two-hit hypothesis states that both alleles of a tumor suppressor gene must be mutated for cancer to occur. If one allele is mutated, expression of the intact allele will prevent aberrant proliferation.
The following finding is observed during a patient’s physical exam. A defect in which of the following is most likely?
This abnormal red reflex can be seen in retinoblastoma (Rb)
This patient has a normal red reflex in their right eye. However, their left eye exhibits leukocoria (white pupil), which is abnormal and indicates something overlying the retina. This abnormal red reflex can be seen in retinoblastoma (Rb), as the tumor is growing on the retina.
Retinoblastoma is a cancer of the eye that develops from mutations of the Rb gene. Normally, Rb proteins bind to and inhibit the transcription factor E2F. While E2F is inhibited, the cell cannot enter S phase.
Without functional Rb proteins, the E2F transcription factor will be unopposed during the G1/S checkpoint, leading to unregulated cellular proliferation.
Key Takeaway:
Retinoblastoma is caused by mutations in the Rb gene.
Abnormal red reflex is a high yield exam finding in retinoblastoma.
The phase of the cell cycle is when the centrioles finish replication.
G2 phase
At the end of the phase of the cell cycle, centrioles begin to replicate.
G1 phase
The DNA of the cell condenses into chromosomes and is pulled apart by the mitotic spindle during .
Mitosis
During phase of interphase, the cell grows and begins to reorganize its contents in preparation for mitosis.
G2 phase
The eukaryotic cell separates its DNA into two identical sets and divides its cytoplasm during the phase of the cell cycle.
mitotic or mitosis
kinases are regulatory proteins that regulate the transition to the S phase of the cell cycle and whose concentrations remain constant.
Cyclin-dependent kinases or CDKs
