Reproduction at the Cellular Level

Reproduction at the Cellular Level

The Cell Cycle

  • Definition: The ordered sequence of events that a cell passes through between one cell division and the next.

Phases of the Cell Cycle

  1. Interphase

    • Subdivided into three phases:

      • G1 Phase: First gap phase, cell grows and synthesizes proteins.

      • S Phase: Synthesis phase where DNA replication occurs.

      • G2 Phase: Second gap phase, cell prepares for mitosis.

  2. Mitotic Phase: The division of the nucleus and cytoplasm.

  3. Cytokinesis: Division of the cytoplasm following mitosis to form two daughter cells.

  4. G0 Phase: A resting phase where the cell is not actively preparing to divide.

Phases of Mitosis in Order

  1. Prophase: Chromatin condenses into visible chromosomes; nuclear envelope breaks down.

  2. Prometaphase: Nuclear envelope is completely gone; microtubules attach to kinetochores.

  3. Metaphase: Chromosomes align at the cell's equatorial plate; metaphase is a checkpoint for chromosomal abnormalities.

  4. Anaphase: Sister chromatids are separated from each other and pulled towards opposite poles of the cell.

  5. Telophase: Chromatids reach poles, the nuclear envelope re-forms around each set of chromosomes.

Characteristics of Cancer Cells

  • Uncontrolled Growth: Cancer cells proliferate without the normal regulatory signals.

  • Ignoring Apoptosis Signals: Cancer cells evade programmed cell death.

  • Angiogenesis: Formation of new blood vessels to supply the tumor.

  • Metastasis: Spread of cancer cells from the original site to other parts of the body.

  • Genomic Instability: Higher mutation rates compared to normal cells.

Cyclins and Cyclin-Dependent Kinases

  • Nature of Regulators: They are positive regulators of the cell cycle, which promote progression through different phases.

Role of Spindle Apparatus

  • Microtubules Attachment: Microtubules of the spindle apparatus attach to kinetochores, which are protein structures on the chromosome.

DNA Replication Timing

  • S Phase: DNA replication occurs specifically during the S phase of the cell cycle.

Location of DNA in Prokaryotic Cells

  • Nucleoid Region: In prokaryotic cells, DNA is found in the nucleoid region, which is an irregularly-shaped section of the cell where the genetic material is located.

DNA Exchange in Prokaryotic Cells

  • Plasmid DNA: Prokaryotic cells can exchange plasmid DNA, which is a small, circular piece of DNA that is separate from the chromosomal DNA.