08_Lecture_Presentation

Introduction

• Cancer cells arise from normal cells due to genetic mutations affecting cell division regulation.

• They exhibit uncontrolled division, potentially invading other tissues and disrupting organ function.

• Despite this, normal cell division is crucial for all life forms.

Key Concepts in Cell Division

8.1 Importance of Cell Division

• Cell division is fundamental for reproduction and the continuation of life; cells come from preexisting cells.

• Asexual Reproduction: Offspring are genetic copies of the parent, resulting in identical progeny.

• Sexual Reproduction: Produces offspring with genetic diversity.

8.2 Prokaryotic Reproduction

• Prokaryotes reproduce asexually via binary fission, meaning they divide in half.

• A single circular DNA molecule replicates, copies move apart, and the cell divides.

8.3 Eukaryotic Chromosomes

• Eukaryotic cells contain more genes organized into multiple chromosomes within a nucleus.

• Chromosomes become visible only during cell division and duplicate to form sister chromatids connected at a centromere.

8.4 The Cell Cycle

• The cell cycle is a sequence of events from cell formation to division.

• Consists primarily of Interphase (G1, S, G2) and the M phase (mitosis).

8.5 Mitosis Process

• Mitosis ensures equal distribution of chromosomes into two daughter nuclei, with key processes including the formation of a mitotic spindle.

• Sister chromatids are separated to opposite poles forming two new nuclei.

8.6 Cytokinesis

• Cytokinesis varies in plant and animal cells:

  • Animal cells: form a cleavage furrow.

  • Plant cells: form a cell plate.

8.7 Regulation of Cell Division

• Environmental factors can influence cell division; for example, cells typically only divide when attached to a surface.

• Growth factors play a key role in regulating the cell cycle at checkpoints.

8.8 Cancer and Cell Division

• Cancer cells proliferate uncontrollably forming tumors, and malignant tumors can invade surrounding tissues.

• Treatments such as radiation and chemotherapy target and disrupt cell division.

Meiosis and Genetic Variation

8.11 Chromosome Pairing

• Somatic (body) cells contain homologous pairs of chromosomes; humans have 46 chromosomes (23 pairs).

8.12 Gametes

• Gametes (eggs and sperm) are haploid, containing a single chromosome set.

• Sexual reproduction alternates between haploid and diploid stages.

8.13 Meiosis Process

• Meiosis involves two divisions, producing four genetically unique haploid cells.

• Crossing over occurs during meiosis I, enhancing genetic variation between sister chromatids.

8.14 Similarities and Differences

• Mitosis creates two identical diploid cells; meiosis yields four unique haploid cells.

8.15 Genetic Variation Mechanisms

• Independent assortment during meiosis and random fertilization contribute to genetic diversity among offspring.

8.17 Genetic Recombination

• Crossing over during prophase I of meiosis increases genetic variability among gametes.

Chromosomal Alterations

8.18 Nondisjunction

• Nondisjunction (failure of chromosomes to separate properly) can lead to abnormal chromosome counts, causing disorders like Down syndrome (Trisomy 21).

8.20 Karyotyping

• A karyotype provides a visual inventory of chromosomes, useful for identifying chromosomal abnormalities.

8.21 Sex Chromosome Abnormalities

• Abnormalities in sex chromosomes may or may not affect survival, with some conditions like Klinefelter syndrome requiring medical attention.

8.22 Evolutionary Implications

• Errors in cell division can lead to the emergence of new species, particularly through polyploidy.

8.23 Structural Changes in Chromosomes

• Rearrangements in chromosome structure can cause genetic disorders or cancer due to deletions, duplications, inversions, or translocations.