Cell Cycle Overview

Cell Cycle

• The cell cycle is a series of events that lead to cell division and duplication. It's a precisely regulated process, ensuring accurate DNA replication and proper chromosome distribution to daughter cells.
• The cell cycle is broadly categorized into interphase and the mitotic (M) phase.
• Interphase, the longest phase, consists of the G1, S, and G2 phases.
  • G1 phase (Gap 1): The cell grows, synthesizes proteins and organelles, and prepares for DNA replication.
  • S phase (Synthesis): DNA replication occurs, creating two identical chromosome copies.
  • G2 phase (Gap 2): The cell continues to grow, synthesizes more proteins and organelles, and checks for DNA replication errors – vital quality control.
• The mitotic (M) phase involves nuclear division (mitosis) followed by cytoplasmic division (cytokinesis).
  • Mitosis: Duplicated chromosomes are separated and distributed into two daughter nuclei. It involves four key stages:
    • Prophase: Chromosomes condense, becoming visible; the nuclear envelope breaks down; the mitotic spindle begins to form.
    • Metaphase: Chromosomes align at the metaphase plate (center of the cell).
    • Anaphase: Sister chromatids separate and move to opposite poles of the cell.
    • Telophase: Chromosomes decondense; nuclear envelopes reform around each chromosome set; the mitotic spindle disappears.
  • Cytokinesis: The cytoplasm divides, creating two separate daughter cells. This process differs between animal and plant cells.
    • Animal cells: A cleavage furrow forms and deepens, eventually pinching the cell in two.
    • Plant cells: A cell plate forms, developing into a new cell wall, separating the two daughter cells.
• Crucial control mechanisms regulate the cell cycle. Checkpoints ensure that DNA replication is complete before mitosis begins, preventing errors.
• Uncontrolled cell growth (cancer) results from compromised cell cycle control mechanisms.

Unit of Life

• A cell serves as the fundamental structural and functional unit of all living organisms.
  • Every organism, whether unicellular or multicellular, is composed of one or more cells.
  • Cells carry out the essential functions of life.
• Types of Cells:
  • Prokaryotic cells lack membrane-bound organelles and a true nucleus. Their DNA is located in a region called the nucleoid. Examples include bacteria and archaea.
  • Eukaryotic cells possess membrane-bound organelles and a distinct nucleus containing the DNA. Examples include animal, plant, fungi and protist cells. Eukaryotic cells are typically larger than prokaryotic cells.
• Key Cellular Structures and their Functions:
  • Cell membrane: A semi-permeable boundary controlling material passage.
  • Nucleus: Houses the genetic material (DNA) and directs cellular activities.
  • Cytoplasm: The region between the nucleus and cell membrane, filled with organelles.
  • Mitochondria: Site of cellular respiration, producing energy.
  • Ribosomes: Involved in protein synthesis.
  • Endoplasmic reticulum (ER): Involved in protein and lipid synthesis. Rough ER (studded with ribosomes) folds and modifies proteins; smooth ER synthesizes lipids and detoxifies substances.
  • Golgi apparatus: Processes, packages, and modifies proteins for secretion or use within the cell.
  • Vacuoles/vesicles: Store substances and facilitate transport. Large central vacuoles are characteristic of plant cells.
  • Chloroplasts (plant cells only): Site of photosynthesis, converting light energy to chemical energy.
  • Cell wall (plant cells only): Provides support and protection to the cell.
• Multicellular Organization: Cells organize into tissues, organs, and organ systems, each with distinct functions.
  • Specialized structures and functions are crucial to individual cells.
  • Coordination and communication between cells are vital for organismal function.