Mitosis in Action by Olivia Hardy

Interphase: G1

olivianhardy06 — 2024-12-09 15:32:58 UTC

The G1 phase, also known as the "Gap 1" phase, is the first stage of the cell cycle in eukaryotes, where the cell grows in size, synthesizes proteins and RNA, and prepares for DNA replication by gathering necessary building blocks, essentially getting ready to enter the DNA synthesis (S) phase. Cyclin-dependent kinases (CDKs) trigger the transition from G1 to S phase and from G2 to M phase by phosphorylating distinct sets of substrates.

Interphase: G0

olivianhardy06 — 2024-12-09 16:34:20 UTC

The G0 phase is a stage in the cell cycle where a cell is not actively dividing or preparing to divide, essentially it is considered a resting state where the cell performs its basic functions without undergoing replication; it exits the cell cycle and enters this phase when not needed to divide, and can re-enter the cycle if stimulated by external signals.

Interphase: G1 checkpoint

olivianhardy06 — 2024-12-09 16:38:12 UTC

The G1 checkpoint, also called the restriction point, is a critical stage in the cell cycle that occurs near the end of the G1 phase, where a cell determines whether conditions are suitable to proceed to DNA replication and commits to cell division. During this checkpoint the cell determines if the cell size, nutrient availability, and DNA integrity are up to par; if these conditions are not met, the cell will be paused at this checkpoint and may attempt to repair issues or exit the cell cycle altogether.

Interphase: S

olivianhardy06 — 2024-12-09 16:40:39 UTC

The S phase, which stands for "synthesis phase," is the stage in the cell cycle where a cell replicates its entire DNA, essentially making an exact copy of its genetic material, ensuring that when the cell divides, each new daughter cell receives a complete set of chromosomes.

Prophase

2024-12-11 03:52:57 UTC

The first stage, prophase, begins with the condensation of chromatin into distinct chromosomes, each consisting of two identical sister chromatids joined at the centromere. The nuclear envelope starts to break down, allowing the chromosomes to interact with the cytoplasmic environment. Meanwhile, the mitotic spindle, a structure composed of microtubules, begins to form from the centrosomes, which have migrated to opposite poles of the cell. These spindle fibers will later attach to the chromosomes, ensuring their proper segregation. Prophase also includes the disassembly of the nucleolus, signifying a shift from cellular metabolism to the mechanics of division.

Metaphase

2024-12-11 03:53:52 UTC

Next is metaphase, a phase characterized by the alignment of chromosomes along the metaphase plate, an imaginary plane equidistant from the spindle poles. Each chromosome's kinetochores, specialized protein structures on the centromeres, attach to spindle fibers emanating from opposite poles. This arrangement ensures that sister chromatids will be pulled to opposite ends of the cell during the subsequent phase. The cell undergoes a critical checkpoint, the spindle assembly checkpoint, to confirm that all chromosomes are properly attached to the spindle apparatus. This ensures accurate chromosome segregation and prevents errors.

Anaphase

2024-12-11 03:54:25 UTC

Anaphase follows, marked by the separation of sister chromatids. Cohesin proteins, which hold the chromatids together, are cleaved, allowing the chromatids to be pulled apart by the spindle fibers. The chromatids, now individual chromosomes, are drawn toward opposite poles of the cell as the microtubules shorten. This movement is facilitated by motor proteins and the depolymerization of microtubules. Simultaneously, the spindle poles themselves move farther apart, elongating the cell and setting the stage for division. Anaphase is critical for ensuring that each daughter cell receives an identical set of chromosomes.

Telophase

2024-12-11 03:54:58 UTC

During telophase, the final stage of mitosis, the chromosomes arrive at the spindle poles and begin to decondense, transitioning back into the less compact chromatin state. The nuclear envelope reassembles around each set of chromosomes, forming two distinct nuclei within the cell. The nucleolus also reappears, signaling the resumption of regular cellular functions. Telophase effectively restores the nuclei to their interphase state, completing the segregation of genetic material.

Cytokinesis

2024-12-11 03:55:35 UTC

Finally, cytokinesis divides the cytoplasm, organelles, and cell membrane to create two distinct daughter cells. In animal cells, a contractile ring composed of actin filaments forms at the cell's equator, constricting to create a cleavage furrow that deepens until the cell splits in two. In plant cells, a cell plate forms along the metaphase plate, eventually developing into a new cell wall that separates the daughter cells. Cytokinesis concludes the cell division process, resulting in two genetically identical daughter cells that are ready to enter interphase and resume their specialized roles.

Interphase: G2

2024-12-11 03:58:06 UTC

Finally, the G2 phase is a period of further growth and preparation for mitosis. The cell continues to synthesize proteins, particularly those needed for spindle formation and chromosomal movement. Organelles like mitochondria and the Golgi apparatus may also increase in number to equip the daughter cells with sufficient cellular machinery. During G2, the cell undergoes another checkpoint to verify the integrity of the replicated DNA and ensure all cellular components are ready for division. If any errors are detected, repair mechanisms are activated to correct them before proceeding to the mitotic phase.

Interphase: G2 checkpoint

olivianhardy06 — 2024-12-12 01:46:51 UTC

The G2 checkpoint is a critical control point in the cell cycle that prevents cells with damaged DNA from entering mitosis. It occurs at the end of the G2 phase, just before the cell enters the mitotic phase and begins cell division. The G2 checkpoint's main role is to ensure that all chromosomes have been accurately replicated without mistakes or damage. If the checkpoint detects any issues, the cell can either delay progression or initiate repair mechanisms.