Chapter8and9

Chapter 8: DNA Replication and Mitosis

Cell Reproduction

• Cell Reproduction: The biological creation of the next generation occurs primarily at the cellular level.

• Importance of Cell Division:

  • Allows growth and reproduction of organisms.

  • Replaces aging or lost cells.

  • Repairs damaged tissue.

Genetic Information

• Genome: Contains all genetic information for an organism.

  • Location: Most genetic information is found in the nucleus of eukaryotic cells.

• Cell Functions:

  • Conduct metabolic activities.

  • Divide during the reproductive phase called mitosis.

The Cell Cycle

• Interphase: Precedes cell division, consisting of three phases:

  • G₁ (gap 1 phase)

  • S (synthesis phase): DNA is copied.

  • G₂ (gap 2 phase).

• Mitosis: Division of the cell.

DNA Replication

• S Phase: DNA replication occurs, using an original DNA molecule as a template to produce two daughter strands.

• Characteristics of DNA Replication:

  • Spreads from specific origin regions.

  • Is bidirectional.

  • Produces two daughter strands via a semiconservative method.

Chromosomes and Chromatin

• Formation: Chromosomes are made up of DNA and histone proteins, which together form chromatin.

  • Active DNA is unwound in interphase; tightly wound during mitosis.

• DNA coiling allows packaging into a tiny nucleus, enabling effective DNA storage.

Sister Chromatids

• Replication: Each chromosome is replicated during the S phase to form sister chromatids.

  • Each daughter cell will receive one of the sister chromatids during mitosis.

Mitosis Overview

• Phases of Mitosis:

  • Prophase: Chromosomes condense and spindle fibers form.

  • Metaphase: Chromosomes align at the cell's equator.

  • Anaphase: Sister chromatids are separated to opposite ends of the cell.

  • Telophase: Nuclei reform and the cell prepares to split.

• Cytokinesis: The final splitting of the cytoplasm, which occurs distinctly in animal (cleavage furrow) and plant cells (cell plate formation).

Cancer Cells

• Cell Cycle Control: The cell cycle regulates development, but cancer can disrupt this through internal and external factors.

  • Can lead to benign or malignant tumors as cells reproduce incorrectly.

• Cancer Treatment: Radiation and chemotherapy target fast-dividing cancer cells but can also affect healthy cells.

• Lifestyle Factors: A healthy lifestyle may reduce cancer risk, emphasizing the importance of check-ups and self-examinations.

Chapter 9: Sexual Reproduction and Meiosis

Types of Reproduction

• Asexual Reproduction: No exchange of genetic material; organisms make copies of themselves.

  • Common in unicellular organisms.

• Sexual Reproduction: Involves genetic material exchange, leading to offspring that are genetically similar but not identical.

  • Fertilization: Combining male and female gametes to produce new organisms.

Meiosis Process**

• Unique Chromosome Sets: Somatic (2n) and reproductive cells (n); humans generally have 46 chromosomes in somatic cells.

• Karyotype: A preparation to determine chromosome number and characteristics.

• Pairing of homologous chromosomes occurs, with specific characteristics in males (XY) and females (XX).

Meiosis I and II

• Meiosis I: Homologous chromosomes pair and separate, preparing for the formation of haploid cells.

• Meiosis II: Sister chromatids separate, resulting in four haploid daughter cells.

Genetic Variation

• Independent Assortment: Chromosome pairs line up independently during meiosis, which increases variability.

• Crossing Over: Chromosomes exchange genetic material during prophase I to form recombinant chromosomes.

• Random Fertilization: Fertilization by one sperm among many creates diversity in genetic combinations.

Errors in Meiosis

• Down Syndrome: Caused by an extra chromosome due to nondisjunction during meiosis.

• Nondisjunction: Failure of chromosome pairs to separate properly during anaphase, leading to abnormal chromosome numbers and potential genetic disorders.