Cell Cycle and Mitosis Stages

• The cell cycle is a repeating series of growth, DNA replication, and division, resulting in two new cells called "daughter" cells
• The cell cycle in eukaryotes involves several phases: G1, S, G2, and M
• G1, S, and G2 are collectively known as interphase
• Eukaryotic cell cycle is regulated by several checkpoints to ensure proper cell division

Phases of the Cell Cycle

• Interphase includes G1, S, and G2 phases
• During interphase, the cell grows and duplicates its chromosomes in preparation for division
• G1 (Gap 1) phase: The cell grows, synthesizes proteins and organelles
• S (Synthesis) phase: DNA replication occurs, resulting in duplicated chromosomes
• G2 (Gap 2) phase: The cell continues to grow, makes more proteins and organelles, and prepares for mitosis

Mitosis Stages

• Mitosis is the process of nuclear division, followed by cytokinesis
• Mitosis consists of several stages: prophase, prometaphase, metaphase, anaphase, and telophase
• Prophase: Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the mitotic spindle forms
• Prometaphase: The nuclear envelope completely breaks down, and spindle microtubules attach to the chromosomes at the kinetochores
• Metaphase: Chromosomes line up at the metaphase plate, ensuring each daughter cell receives the same number of chromosomes
• Anaphase: Sister chromatids separate and move to opposite poles of the cell
• Telophase: Chromosomes arrive at the poles, the nuclear envelope reforms, and chromosomes decondense
• Cytokinesis typically occurs after telophase, dividing the cytoplasm and forming two separate daughter cells

Regulation of Cell Division

• Cell division is tightly regulated to ensure proper growth and development
• Several factors can influence cell division, including growth factors, cell size, and DNA damage
• Growth factors stimulate cell division by binding to receptors on the cell surface and activating intracellular signaling pathways
• Cell size: Cells often need to reach a certain size before they can divide; this prevents premature division
• DNA damage: The cell cycle can be arrested if DNA damage is detected, allowing time for repair before replication or division

Cell Cycle Checkpoints

• Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division
• There are three major checkpoints: the G1 checkpoint, the G2 checkpoint, and the spindle checkpoint
• G1 checkpoint: Occurs at the end of the G1 phase and determines whether the cell will proceed into S phase
• G1 checkpoint assesses DNA damage, cell size, and the availability of nutrients and growth factors
• If conditions are unfavorable, the cell may enter a resting state called G0 or undergo apoptosis
• G2 checkpoint: Occurs at the end of the G2 phase and ensures that DNA replication is complete and that there is no DNA damage
• If problems are detected, the cell cycle is arrested to allow for repair
• Spindle checkpoint: Occurs during metaphase and ensures that all chromosomes are properly attached to the spindle microtubules
• This prevents premature entry into anaphase and ensures that each daughter cell receives the correct number of chromosomes