S Phase

Definition

The S phase, or synthesis phase, is the part of the cell cycle where DNA replication occurs, resulting in the duplication of chromosomes. This phase is critical because it ensures that each daughter cell will receive an exact copy of the genetic material during cell division. The S phase follows the G1 phase and precedes the G2 phase, and it is tightly regulated to prevent errors in DNA replication.

5 Must Know Facts For Your Next Test

1. During the S phase, each chromosome is duplicated, resulting in two sister chromatids for each chromosome that are held together at a region called the centromere.
2. The duration of the S phase can vary significantly among different cell types, typically lasting several hours in actively dividing cells.
3. Key proteins called cyclins and cyclin-dependent kinases (CDKs) are crucial for regulating the progression through the S phase, ensuring that DNA replication occurs accurately.
4. Errors in DNA replication during the S phase can lead to mutations or chromosomal abnormalities, highlighting the importance of precise mechanisms in this phase.
5. After the S phase is completed, cells enter the G2 phase, where they prepare for mitosis by further checking DNA for any errors and ensuring all necessary proteins are present.

Review Questions

• How does the S phase contribute to genetic consistency during cell division?
  • The S phase is essential for maintaining genetic consistency because it is when DNA replication occurs. Each chromosome is duplicated so that when a cell divides, both daughter cells receive identical genetic material. This replication ensures that all necessary genetic information is passed on accurately, which is crucial for the proper functioning of cells and organisms.
• Discuss the role of regulatory proteins in ensuring accurate DNA replication during the S phase.
  • Regulatory proteins such as cyclins and cyclin-dependent kinases (CDKs) play a vital role in overseeing DNA replication during the S phase. These proteins help coordinate the timing of replication and ensure that it proceeds without errors. They do this by activating or inhibiting various factors involved in DNA synthesis, thus maintaining fidelity during this critical period of the cell cycle.
• Evaluate how defects in the S phase can lead to long-term consequences for an organism's health.
  • Defects in the S phase can have serious long-term consequences for an organism's health because improper DNA replication can lead to mutations, chromosomal abnormalities, or cancer. If errors occur during this phase and are not corrected, they can be propagated through subsequent generations of cells. This accumulation of mutations can disrupt normal cellular functions and lead to uncontrolled growth or other diseases, underscoring the importance of precise regulation during this part of the cell cycle.

Related terms

Cell Cycle: The series of events that cells go through as they grow and divide, including phases like G1, S, G2, and M.

DNA Replication: The process by which a cell makes an identical copy of its DNA before cell division.

Checkpoint: Regulatory points in the cell cycle that ensure proper progression and integrity of the cell's genetic material before moving on to the next phase.