Ch.8 DNA Replication and Viruses Flashcards/Notes- Honey Ortiz

Chapter 8: DNA Replication

Semiconservative Model

  • DNA replication is a key cellular process wherein a cell copies its DNA.

  • In this model, each DNA molecule consists of 50% old (parental) DNA and 50% new (daughter) DNA.

  • The two parental strands separate and act as templates for new strand synthesis.

  • The base pairing rule (A-T and G-C) must be followed during this process.

Mechanism of DNA Replication

  • The process involves:

    • Original Template Strands: Each of the original strands of the double helix serves as a template for the new strands.

    • Base Pairing: Nucleotides must adhere to the base pair rules, contributing to accurate replication of the DNA sequence.

    • Directionality: The strands run in an anti-parallel direction, with one strand oriented 5' to 3' and the other 3' to 5'.

Enzymes in DNA Replication

  • DNA Helicase: “Unzips” the DNA helix by breaking hydrogen bonds between base pairs.

    • This unwinding separates the parental strands, preparing them for replication.

  • DNA Polymerase: carries out synthesis of new DNA

    • Synthesizes new DNA strands based on the template strand.

    • Requires a primer (a short strand of nucleotides) to initiate synthesis.

    • Follows the base pairing rule during strand elongation.

    • Proofreads newly synthesized DNA to correct mismatched pairs and errors.

  • The daughter strands that are made are IDENTICAL to the parent strands because its a REPLICATION.

Errors in DNA Replication

  • Potential Mistakes: Can include wrong base addition, missed nucleotides, or extra nucleotides slipping into the sequence.

  • Errors arise partly due to the rapid action of DNA polymerases.

  • Replication errors can exacerbate if DNA has been previously damaged.

DNA Repair Mechanisms

  • Most DNA polymerases have proofreading abilities to correct imperfections.

  • other repair enzymes act by:

    • Detecting and repairing damaged sections of DNA.

    • For instance:

      • UV-induced damage is rectified by excising the damaged region; DNA polymerase then fills in the gaps with the correct nucleotides.

Mutations

  • If errors in replication remain uncorrected, they become mutations
    if DNA polymerase or repair enzyme can’t “fix” the error, they become mutations:

    • Defined as permanent changes in the DNA sequence that can impact gene function.

    • Mutations affect diverse cell types and can be hereditary if they arise during gamete formation.

    • They can lead to harmful consequences, including the initiation of cancers.

    • While many mutations are detrimental, some contribute to genetic variation, acting as a basis for evolution.

Viruses and DNA

  • Viruses can introduce new genetic material into cells. This is achieved when viral RNA or DNA integrates into the host cell's genetic framework.

  • Viruses consist mainly of:

    • Genetic material (either DNA or RNA)

    • A protective protein coat

    • Occasionally, other components.

Types of Viruses

  • Plant Viruses: Target only plant cells.

  • Bacteriophages: Infect bacterial cells.

  • Animal Viruses: Bind to various animal cell types.

Viral Replication Process

  1. Attachment: Virus binds to cell surface receptors.

  2. Penetration: Viral nucleic acid is released inside the host cell.

  3. Synthesis: Host cellular machinery produces viral nucleic acids and proteins.

  4. Assembly: Complete viruses are formed from synthesized components.

  5. Release: New viruses exit the host cell to infect other cells.

Conclusion

  • Understanding DNA replication and repair mechanisms is crucial for comprehending how genetic information is maintained, altered, and propagated across generations, as well as the implications of errors such as mutations in both health and disease contexts.


    part 2:

    Cell Reproduction Notes

    Key Concepts

    • Introduction to the Cell Cycle

    • Mitosis

    • Cytokinesis

    • Cancer

    Cells

    • Origin of Cells: All cells originate from other cells through division. Eukaryotic cell division occurs via mitosis and meiosis.

    • Functions of Cell Division: Essential for growth, maintenance, and repair of tissues in multicellular organisms.

    Cellular Organization of Genetic Material

    • Eukaryotic Chromosomes: Composed of chromatin, which is a combination of DNA and proteins.

    • Chromatin Behavior:

    • In non-dividing cells, chromosomes exist as long, thin chromatin fibers.

    • Upon cell division preparation, chromatin condenses to form discrete chromosomes.

    Understanding Chromosomes

    • Homologous Chromosomes: Chromosome pairs in diploid organisms, with one set inherited from each parent.

    • Somatic Cells:

    • Diploid (2n) cells, contribute to body tissues, not involved in reproduction.

    • Humans possess 46 chromosomes (23 pairs).

    • Gametes:

    • Haploid (n) cells involved in sexual reproduction, containing one set of chromosomes.

    • Includes sex chromosomes (X and Y in humans).

    The Cell Cycle

    • Definition: The cell cycle outlines the life of a cell from its formation to its division into two new cells.

    • Phases of the Cell Cycle:

    • Interphase: Cell growth where DNA is in chromatin form. LONGEST PHASE It consists of three stages:

      • G1 phase (First Gap): Increased cell growth and metabolism.

      • S phase (Synthesis): DNA is replicated (chromosome duplication).

      • G2 phase (Second Gap): Further growth and preparation for mitosis.

    • Mitosis: Nuclear division that includes the following stages:

      1. Prophase: Chromosomes condense; spindle formation begins.

      2. Metaphase: Chromosomes align at the cell's equatorial plane.

      3. Anaphase: Sister chromatids are pulled apart toward opposite poles.

      4. Telophase: Formation of two new nuclei as chromosomes de-condense.

    • Cytokinesis: Division of cytoplasm occurring post-telophase; different in animals (cleavage furrow) and plants (cell plate formation).

    Cytokinesis in Detail

    • Animal Cells:

    • Division through a cleavage furrow that pinches the cell into two.

    • Plant Cells:

    • Formation of a cell plate from Golgi vesicles that eventually forms the new cell wall.

    Cell Cycle Overview

    • During G1, homologous chromosomes are present; in G2, each consists of two DNA molecules (sister chromatids).

    • Mitosis and cytokinesis result in two genetically identical daughter cells.

    Prokaryotic Cell Division

    • Binary Fission: Method of cell division in prokaryotes resulting in two identical daughter cells; faster and less energy-intensive than eukaryotic division.

    Cell Cycle Control System

    • Major checkpoints exist at G1, S, G2, and M phases to ensure proper regulation of cell division.

    • Cells can enter a resting state (G0) for non-dividing circumstances.

    Uncontrolled Cell Cycle

    • If regulation fails, normal cells may transform into cancer cells, leading to uncontrolled division.

    • Cancer Characteristics:

    • Cancer cells often lack specialized functions and consume resources inefficiently.

    • Immune Response: Typically targets these abnormal cells, but cancer cells may evade detection leading to rapid growth.

    Cancer

    • Tumors: Masses of abnormal cells that arise from cancerous transformations.

    • Benign Tumor: Harmless growth that stays localized.

    • Malignant Tumor: Can spread (metastasize) to other body parts, posing greater health threats.

    • Types of Skin Cancer:

    • Basal Cell Carcinoma: Most common, slow growing.

    • Melanoma: Most aggressive, can spread rapidly.

    • Squamous Cell Carcinoma: Second most common, appears as firm, pink growths under the skin.