S Phase

Definition

The S phase, or synthesis phase, is a critical part of the cell cycle where DNA replication occurs, leading to the duplication of chromosomes. This phase ensures that each daughter cell receives an identical set of genetic information during cell division, which is essential for maintaining genetic stability and proper cellular function.

5 Must Know Facts For Your Next Test

1. During the S phase, each chromosome is replicated, resulting in two sister chromatids that are joined at the centromere.
2. The duration of the S phase can vary significantly among different cell types, with some cells completing it quickly while others take longer.
3. DNA repair mechanisms are highly active during the S phase to correct any replication errors and prevent mutations.
4. S phase is tightly regulated by various checkpoints to ensure that DNA replication is completed accurately before the cell proceeds to mitosis.
5. If DNA damage is detected during S phase, the cell can activate repair pathways or trigger apoptosis to prevent the propagation of damaged DNA.

Review Questions

• How does the S phase contribute to genetic stability during cell division?
  • The S phase is crucial for genetic stability because it is when DNA replication occurs, ensuring that each daughter cell receives an identical set of chromosomes. By duplicating the genetic material accurately, it prevents loss or alteration of vital information needed for proper cellular function. This process is tightly controlled to minimize errors, thereby safeguarding against mutations that could lead to diseases.
• Discuss the regulatory mechanisms that control the transition from G1 to S phase and their significance.
  • The transition from G1 to S phase is controlled by various regulatory mechanisms, primarily involving cyclins and cyclin-dependent kinases (CDKs). These proteins ensure that conditions are favorable for DNA replication, such as sufficient nutrients and growth factors. If these conditions are not met, checkpoints can halt the cycle to prevent cells from entering S phase under unfavorable circumstances, thereby protecting against potential DNA damage or replication errors.
• Evaluate the impact of malfunctioning checkpoints during the S phase on cancer development.
  • Malfunctioning checkpoints during the S phase can lead to uncontrolled cell division and contribute to cancer development. When checkpoints fail, cells may replicate damaged or mutated DNA without repair, leading to genomic instability. This can promote oncogenic transformations as cells accumulate mutations over time. Understanding these processes highlights potential therapeutic targets for cancer treatments that aim to restore proper checkpoint function.

Related terms

G1 Phase:

The first gap phase of the cell cycle where the cell grows and prepares for DNA synthesis.

G2 Phase:

The second gap phase that follows the S phase, where the cell continues to grow and prepares for mitosis.

Cyclins:

Regulatory proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinases (CDKs).