DNA Replication, Binary Fission, and Mitosis

Chapter 8: DNA Replication, Binary Fission, and Mitosis

Section 8.1: Cells Divide, and Cells Die

  • Cells undergo a continuous cycle of dying and being replaced.
  • Roles of Cell Division:
    • Reproduction
    • Growth
    • Development
  • Cell division occurs via two mechanisms:
    • Mitosis: Responsible for clonal reproduction.
    • Meiosis: Produces sex cells.

Section 8.1: Mitosis Has Many Roles

  • Functions of Mitotic Cell Division:
    • Facilitates growth and development.
    • Repairs tissues.
    • Regenerates lost body parts.
  • Some organisms reproduce asexually through mitosis.

Section 8.1: Cell Death Is Part of Life

  • Apoptosis: Defined as programmed cell death, critical for maintaining the structure and function of tissues.
    • Is responsible for shaping tissues and eliminating damaged cells.

Section 8.1: Mitosis and Apoptosis Work Together

  • Mitosis and apoptosis function in opposition to maintain tissue homeostasis:
    • Mitosis creates new cells.
    • Apoptosis removes old or damaged cells.

Section 8.1: Mastering Concepts

  • Analyze how mitotic cell division, meiosis, and fertilization interconnect within the human life cycle.

Section 8.2: DNA Replication Precedes Cell Division

  • For daughter cells to inherit identical DNA, the genome must be replicated prior to cell division.
  • Steps of DNA Replication:
    1. Strands unwind and separate.
    2. Each strand serves as a template that binds complementary nucleotides (A-T and G-C pairing).
    3. Results in double-stranded DNA composed of one parental and one daughter strand, termed semiconservative replication.

Section 8.2: Denaturation

  • Denaturation: Process of unwinding DNA, allowing templates to become accessible for replication.

Section 8.2: Enzymes in DNA Replication

  • Helicases: Unwind the DNA double helix.
  • Binding proteins: Stabilize separated strands during unwinding.
  • Primase: Adds a short RNA primer complementary to the template strand.
  • DNA Polymerase: Extends the new DNA strand by adding nucleotides that are complementary to the template strand.

Section 8.2: Directionality of DNA Replication

  • Nucleotides are added at the 3' end of the new DNA strand.
  • Note that DNA polymerase functions in opposite directions on each strand:
    • Leading Strand: Continuously synthesized as DNA unwinds.
    • Lagging Strand: Synthesized discontinuously in fragments known as Okazaki fragments.

Section 8.2: Termination of DNA Synthesis

  • After synthesis, an enzyme replaces the RNA primer with DNA.
  • Ligases: Connect the DNA fragments together by forming covalent bonds.

Section 8.2: Origins of Replication

  • DNA replication initiates simultaneously at multiple Origins of Replication leading to the formation of two identical DNA molecules.

Section 8.3: Prokaryotes Divide by Binary Fission

  • Binary Fission: A method of asexual reproduction in prokaryotes that replicates DNA and distributes it into two daughter cells that are genetically identical to the original.

Section 8.3: Mastering Concepts

  • Outline the sequential events in binary fission.

Section 8.4: Eukaryotic Cells and Mitosis

  • Eukaryotic cell division is facilitated through mitosis, unlike binary fission in prokaryotes.

Section 8.4: Chromosome Condensation Prior to Cell Division

  • Before eukaryotic cell division, the DNA condenses into discernible chromosomes.
  • Naked DNA wraps around nucleosomes, clusters of histone proteins, to form compact structures necessary for division.

Section 8.4: Formation of Chromatin

  • Nucleosomes cluster into chromatin, which is tightly packed by scaffold proteins.
  • The condensation of chromatin into chromosomes occurs to facilitate easier movement during cell division.

Section 8.4: Mastering Concepts

  • Describe the relationship between chromosomes and chromatin.

Section 8.5: The Cell Cycle

  • The cell cycle encompasses the events that transpire during a complete round of cell division.
  • Phases of the Cell Cycle:
    • Interphase: Cell engages in DNA replication (S phase) and normal functions.
    • G1 Phase: Normal growth and function with ongoing protein synthesis.
    • G0 Phase: A resting state where the cell does not divide or replicate DNA.
    • S Phase: DNA replication occurs, resulting in duplicated chromosomes.
    • G2 Phase: Continued growth with preparation for mitosis.
    • Mitosis Phase: Actual division of the nucleus followed by cytokinesis (division of the cytoplasm).

Section 8.5: Stages of Mitosis

  • Mitosis consists of several key stages:
    • Prophase
    • Prometaphase
    • Metaphase
    • Anaphase
    • Telophase

Section 8.5: Cytokinesis

  • In animal cells, cytokinesis is indicated by the formation of a cleavage furrow, which deepens as protein rings contract beneath the cell membrane.

Section 8.5: Mastering Concepts

  • What are the critical events occurring during each stage of mitosis?

Section 8.6: Cancer and the Cell Cycle

  • Cancer arises when cells divide uncontrollably, often bypassing the regulatory checkpoints that monitor the health and status of the cell cycle.

Section 8.6: Checkpoints in the Cell Cycle

  • G1 Checkpoint: Assesses DNA for damage.
  • S Phase Checkpoint: Determines if DNA is replicating correctly.
  • G2 Checkpoint: Checks for complete DNA replication and potential repairs for damaged DNA, along with confirming spindle formation.
  • Metaphase Checkpoint: Verifies spindle formation, chromosome attachment, and alignment.

Section 8.6: Tumor Development

  • Tumors consist of masses of tissue where cells divide uncontrollably, categorized as benign or malignant.
  • Tumors can originate from
    • Overactive proto-oncogenes.
    • Underactive tumor suppressor genes.
  • Risk factors for cancer can be genetic or environmental.
  • Treatment options include surgery, chemotherapy targeting cancer cells, and radiation.

Section 8.7: Apoptosis - Programmed Cell Death

  • Apoptosis is a regulated process that dismantles cells, playing a crucial role in eliminating excess or defective cells while shaping appropriate structures during development.

Section 8.7: Investigating Cancer Treatment

  • Drug classes target tumor vascular supply rather than directly attacking cancer cells.
  • By targeting the blood vessels that supply nutrients to tumors, these drugs can effectively stall tumor growth.
  • Endostatin: Targeted therapy that reduced tumor growth in animal models.
  • Traditional chemotherapy, while effective in delaying cancer, does not fully eradicate it.