Quiescent cells belong to which phase of cell cycle?
Quiescent cells are those that are not actively dividing. I remember that G0 is the phase where cells exit the cell cycle and remain in a resting state. So quiescent cells would be in G0. But wait, sometimes people confuse G0 with G1. Let me make sure. The G1 phase is the first growth phase where the cell grows and prepares for DNA synthesis. If a cell is not going to divide, it can leave G1 and enter G0. So the quiescent state is G0.
Looking at the options, the correct answer should be the option that says G0. Now, the other options might be G1, S, G2, or M. Let's break them down. If an option is G1, that's incorrect because quiescent cells are in G0, not G1. The S phase is where DNA synthesis occurs, so that's not it. G2 is the second growth phase before mitosis, so also not quiescent. M phase is mitosis, definitely not.
The core concept here is understanding the cell cycle phases and the G0 quiescent state. The key is knowing that G0 is the resting phase outside the active cell cycle phases. The clinical pearl would be that G0 is where cells exit the cycle, like in mature neurons or muscle cells, which don't divide. So the answer is G0.
**Core Concept**
Quiescent cells are in the **G0 phase**, a resting state outside the active cell cycle phases (G1, S, G2, M). This phase is characterized by metabolic activity without cell division, often seen in mature differentiated cells.
**Why the Correct Answer is Right**
G0 is the phase where cells exit the cell cycle to maintain a non-proliferative state. This occurs when cells receive signals to halt division (e.g., contact inhibition, nutrient scarcity). Unlike G1 (pre-DNA synthesis growth), G0 cells do not progress to S phase. Examples include post-mitotic cells like neurons and myocytes.
**Why Each Wrong Option is Incorrect**
**Option A:** G1 phase involves active growth and preparation for DNA replication, not quiescence.
**Option B:** S phase is DNA synthesis; quiescent cells do not replicate DNA.
**Option C:** G2 phase occurs after DNA replication and before mitosis, unrelated to quiescence.
**Clinical Pearl / High-Yield Fact**
Mature cells (e.g., neurons) permanently reside in G0, while others may re-enter the cycle under stress or injury. G0 arrest is a key target in cancer therapy to prevent uncontrolled proliferation.
**Correct Answer: D. G0**