Cell cycle

The cell cycle is the ordered series of phases that a cell goes through to grow and divide into two daughter cells. In eukaryotes, the cell cycle consists of interphase (G1, S, and G2) followed by the mitotic (M) phase (when nuclear division, i.e., mitosis, occurs, and usually cytokinesis, division of the cytoplasm). The cycle ensures that DNA is duplicated during S phase and properly segregated during M phase, with checkpoints along the way to maintain fidelity.

• Main stages to remember: Interphase = G1 + S + G2, where the cell grows and duplicates DNA; M phase = Mitosis (+ Cytokinesis), where the cell actually divides. Sometimes you'll see M phase broken down into prophase, metaphase, etc., but in the context of the cell cycle as a whole, M is the division stage.
• Cells can exit the cycle after mitosis and enter G0 (a resting state) if they are not going to divide again soon. Not all cells are continuously cycling; many adult cells stay in G0 until they get signals to re-enter G1 and divide.
• There are built-in checkpoints: at G1 (ensuring the cell is ready for DNA replication), at G2 (ensuring DNA replicated correctly and cell is ready for mitosis), and during M (the spindle checkpoint in metaphase ensures all chromosomes are properly attached to spindle fibers before anaphase). These checkpoints prevent errors like damaged DNA being passed on or chromosome mis-segregation.
• In an exam context, knowing the chronological order of the cell cycle is fundamental. Also, an integrated understanding: e.g., DNA content changes - it doubles in S and halves after cytokinesis; or that certain proteins (cyclins/Cdks) regulate progression - though detailed biochem of regulation might be beyond premed scope, a basic mention could appear.

• Expect general questions like "What are the phases of the eukaryotic cell cycle?" or "During which phase is DNA replicated, and during which phase do chromosomes segregate?" - You'd answer: DNA is replicated in S (during interphase), chromosomes segregate in M (mitosis).
• Graph-based questions: You might get a plot of DNA content over time or a pie chart of a cell population in different phases. Recognize that the largest fraction of cells is usually in G1 (for a typical actively dividing population), and the DNA content doubles during S, is highest in G2/M, then drops back after division.
• If a question mentions drugs: e.g., "Drug X halts the cell cycle by preventing formation of microtubules." That would block cells in M phase (since microtubules form the spindle). Or a drug that inhibits DNA polymerase would stall cells in S phase. Understanding the cell cycle helps deduce at which phase a cell is stopped by a given treatment.
• Sometimes questions use cell cycle to frame concepts of cancer. Cancer cells often have dysregulated cell cycle checkpoints, leading to uncontrolled division. A question might ask which checkpoint failure could lead to replication of damaged DNA (answer: G1 or G2 checkpoints failing). This ties cell cycle knowledge to pathology.