Untitled Flashcards Set

Cell Division: A Comprehensive Study Guide

🔬 Prokaryotic Cell Division: Binary Fission

Binary Fission: The process of cell division in prokaryotic cells (bacteria and archaea). It's a simpler process than eukaryotic cell division.

Steps of Binary Fission:

1. DNA Replication: The single circular chromosome replicates, starting at the origin of replication.

2. Chromosome Segregation: The two replicated chromosomes move to opposite ends of the elongating cell. This is often facilitated by attachment to the cell membrane.

3. Cytokinesis: The cell membrane pinches inward, dividing the cytoplasm and forming two identical daughter cells, each with a copy of the chromosome.

Advanced Concepts: The precise mechanisms of chromosome segregation in binary fission are still being researched. Factors like the involvement of specific proteins and the role of the cytoskeleton are areas of active investigation.

🧬 Eukaryotic Cell Division: An Overview

Eukaryotic cells divide through more complex processes: mitosis and meiosis. These processes are crucial for growth, repair, and sexual reproduction.

Mitosis: A type of cell division that produces two identical daughter cells from a single parent cell. It's essential for growth and repair in multicellular organisms.

Meiosis: A type of cell division that produces four genetically diverse haploid gametes (sex cells) from a single diploid parent cell. It's the basis of sexual reproduction.

Key Differences between Mitosis and Meiosis:

🔄 The Cell Cycle: Interphase and the Mitotic Phase

The cell cycle is the series of events that take place in a cell leading to its division and duplication. It consists of two main phases:

Interphase: The longest phase of the cell cycle, during which the cell grows, replicates its DNA, and prepares for division. It's subdivided into G1 (gap 1), S (synthesis), and G2 (gap 2) phases.

Mitotic Phase (M phase): The phase of the cell cycle during which cell division occurs. It includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Interphase Details:

• G1 (Gap 1): Cell growth, organelle production, and normal cellular functions. The cell checks for DNA damage before proceeding to the S phase.

• S (Synthesis): DNA replication occurs, creating two identical copies of each chromosome (sister chromatids).

• G2 (Gap 2): Further cell growth, preparation for mitosis, and another checkpoint to ensure DNA replication was successful.

Checkpoints: The cell cycle is regulated by checkpoints that ensure the cell is ready to proceed to the next stage. These checkpoints monitor DNA integrity and cell size.

🔬 Mitosis: Stages and Mechanisms

Mitosis is a continuous process, but it's divided into distinct stages for descriptive purposes:

Prophase: Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the mitotic spindle begins to form.

Prometaphase: The nuclear envelope fragments completely, and microtubules from the spindle attach to the kinetochores of the chromosomes.

Metaphase: Chromosomes align at the metaphase plate (the equator of the cell), ensuring each daughter cell receives one copy of each chromosome.

Anaphase: Sister chromatids separate and move to opposite poles of the cell, pulled by the shortening microtubules.

Telophase: Chromosomes arrive at the poles, the nuclear envelope reforms around each set of chromosomes, and the chromosomes begin to decondense.

Cytokinesis: The cytoplasm divides, resulting in two separate daughter cells, each with a complete set of chromosomes. In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms.

Advanced Concepts: The mitotic spindle is a dynamic structure composed of microtubules and associated proteins. Motor proteins play a crucial role in chromosome movement during anaphase.

🔀 Meiosis: Reductional and Equational Divisions

Meiosis involves two rounds of division: Meiosis I and Meiosis II.

Meiosis I (Reductional Division): This division reduces the chromosome number from diploid (2n) to haploid (n). Homologous chromosomes pair up, and crossing over occurs.

Meiosis II (Equational Division): This division is similar to mitosis, but it starts with haploid cells. Sister chromatids separate, resulting in four haploid daughter cells.

Stages of Meiosis I:

• Prophase I: Homologous chromosomes pair up (forming tetrads), crossing over occurs (exchange of genetic material between non-sister chromatids).

• Metaphase I: Tetrads align at the metaphase plate.

• Anaphase I: Homologous chromosomes separate and move to opposite poles.

• Telophase I & Cytokinesis: Two haploid daughter cells are formed.

Stages of Meiosis II: Similar to mitosis, but with haploid cells. Sister chromatids separate, resulting in four haploid daughter cells.

Advanced Concepts: The mechanisms of crossing over and the regulation of meiosis are complex and involve many genes and proteins. Errors in meiosis can lead to aneuploidy (abnormal chromosome number).

🧬 Genetic Variation in Sexual Reproduction

Sexual reproduction generates genetic variation through several mechanisms:

Independent Assortment: During meiosis I, homologous chromosomes align randomly at the metaphase plate. This leads to different combinations of maternal and paternal chromosomes in the daughter cells.

Crossing Over: The exchange of genetic material between non-sister chromatids during Prophase I of meiosis. This creates recombinant chromosomes with new combinations of alleles.

Random Fertilization: The fusion of two gametes (sperm and egg) during fertilization is a random event. This further increases the genetic diversity of offspring.

Advanced Concepts: The extent of genetic variation generated by sexual reproduction is enormous, contributing to the adaptability of populations. The interplay between these mechanisms creates a vast array of possible genotypes in offspring.

🔬 Errors in Cell Division: Nondisjunction and Chromosomal Aberrations

Errors during cell division can lead to serious consequences:

Nondisjunction: The failure of chromosomes or chromatids to separate properly during meiosis or mitosis. This can result in aneuploidy (abnormal chromosome number) in daughter cells.

Chromosomal Aberrations: Changes in chromosome structure, such as deletions, duplications, inversions, and translocations. These can alter gene expression and function.

Types of Chromosomal Aberrations:

Aberration Description Consequences Deletion Loss of a chromosomal segment Loss of gene function, potentially lethal Duplication Repetition of a chromosomal segment Altered gene dosage, potential developmental effects Inversion Reversal of a chromosomal segment Altered gene order, potential disruption of gene function Translocation Movement of a chromosomal segment to a nonhomologous chromosome Altered gene expression, potential cancer risk

Facts to Memorize:

1. Binary fission is the primary method of cell division in prokaryotes.

2. Mitosis produces two genetically identical diploid daughter cells.

3. Meiosis produces four genetically unique haploid daughter cells.

4. The cell cycle consists of interphase and the mitotic phase.

5. Interphase includes G1, S, and G2 phases.

6. The stages of mitosis are prophase, prometaphase, metaphase, anaphase, and telophase.

7. Cytokinesis is the division of the cytoplasm.

8. Meiosis I is the reductional division, and Meiosis II is the equational division.

9. Crossing over occurs during Prophase I of meiosis.

10. Independent assortment occurs during Metaphase I of meiosis.

11. Random fertilization contributes to genetic variation.

12. Nondisjunction is the failure of chromosomes to separate properly.

13. Aneuploidy is an abnormal chromosome number.

14. Chromosomal aberrations include deletions, duplications, inversions, and translocations.

15. Polyploidy is the condition of having more than two sets of chromosomes.

16. Cell division is regulated by checkpoints that monitor DNA integrity and cell size.

17. Growth factors and anchorage dependence influence cell division in animal cells.

18. Density-dependent inhibition prevents excessive cell growth.

19. Cancer is characterized by uncontrolled cell division.

20. Homologous chromosomes carry the same genes but may have different alleles.