Cell Cycle Overview: Interphase and M Phase
📌 The cell cycle is divided into two main phases: Interphase (preparation) and M Phase (mitosis, the actual division).
⏳ Interphase is the longest phase, lasting about 20 hours, while the M phase (Mitosis) is much shorter, lasting only 1 to 2.5 hours.
🌱 Interphase consists of three sub-phases: G₁ phase, S phase (Synthesis), and G₂ phase.
🧬 Mitosis (M phase) includes Karyokinesis (nuclear division) and Cytokinesis (cytoplasmic division).

Interphase Details (G₁, S, G₂)
⏱️ The G₁ phase involves an increase in cell size and synthesis of RNA and proteins, typically lasting 8 hours.
🧬 The S phase is dedicated to DNA replication (duplication) and the duplication of the centrioles, also lasting about 8 hours.
🛠️ The G₂ phase lasts about 4 hours and involves the synthesis of more RNA, proteins, and crucial proteins like tubulin needed for the mitotic spindle.
📈 The duration of G₁ phase varies significantly depending on the cell type; highly proliferative cells (e.g., bone marrow stem cells) have a short G₁, while specialized cells like nerve or heart cells may enter a prolonged G₀/G₁ state.

Mitosis (M Phase) Stages: Karyokinesis
🔬 Karyokinesis, the division of the nucleus, proceeds through four stages summarized by the mnemonic "PMAT": Prophase, Metaphase, Anaphase, and Telophase.
🌀 In Prophase, chromosomes condense (become visible as sister chromatids/diploid chromosomes), the nuclear envelope begins to break down, and centrioles migrate to opposite poles.
📏 In Metaphase, chromosomes align along the equatorial plane (metaphase plate), and the mitotic spindle fibers attach to the kinetochores.
✂️ Anaphase is characterized by the separation of sister chromatids, resulting in 92 single chromatids (now considered individual chromosomes) migrating to opposite poles, 46 moving to each side.
🔙 Telophase involves the chromosomes arriving at the poles, the reformation of the nuclear envelope and nucleoli, and the beginning of cleavage furrow formation.

Mitosis Stages: Cytokinesis
🌊 Cytokinesis follows Karyokinesis, involving the physical division of the cytoplasm.
➰ This is initiated by the formation of a cleavage furrow which deepens due to a contractile ring composed of actin and myosin filaments.
✌️ The result of successful mitosis and cytokinesis is the formation of two genetically identical daughter cells, each with 46 single chromosomes (2n).

Key Points & Insights
➡️ The S phase is critical for duplication; it involves duplicating both the DNA and the centrioles (forming two pairs of centrioles/centrosomes).
➡️ Microtubules are organized into three types during Mitosis: Chromosome (Kinetochore) microtubules that attach to chromosomes, Polar microtubules connecting opposite poles, and Astral microtubules radiating outwards from the centrosomes.
➡️ Cell state is defined by ploidy and DNA content: In G₁ (46 single chromosomes), the cell is 2n (diploid) and 2C DNA content (implied). After S phase (46 double chromosomes), it's still 2n but effectively 4C DNA content until division.
➡️ The Anaphase stage briefly results in a 4n DNA content state momentarily within the single dividing cell structure (92 single chromosomes/chromatids).

📸 Video summarized with SummaryTube.com on Nov 16, 2025, 14:15 UTC