Cell Cycle, Binary Fission, and Mitosis: Study Guide

Study Guide - Smart Notes

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Understanding cell division requires familiarity with several fundamental terms:

Chromosome: A DNA molecule with associated proteins, carrying genetic information.
Chromatin: The complex of DNA and proteins that forms chromosomes within the nucleus.
Centromere: The region of a chromosome where sister chromatids are joined and where spindle fibers attach during mitosis.
Centrosome: The organelle that serves as the main microtubule organizing center; important for spindle formation.
Centrioles: Cylindrical structures within the centrosome, involved in organizing microtubules.
Gene: A segment of DNA that codes for a specific protein or functional RNA.
Allele: Different versions of a gene found at the same locus.
Duplicated chromosome: A chromosome that has undergone DNA replication, consisting of two sister chromatids.
Sister chromatid: Each of the two identical copies of a chromosome, joined at the centromere.
Homologous chromosomes (homologues): Chromosome pairs, one from each parent, that are similar in shape, size, and genetic content.
Diploid: Cells with two sets of chromosomes (2n), typical of somatic cells.
Haploid: Cells with one set of chromosomes (n), typical of gametes.

Growth: Expansion of multicellular organisms.
Replacement/Maintenance: Renewal of tissues and repair of damage.
Asexual Reproduction: Production of genetically identical offspring.
Preparation for Sexual Reproduction: Formation of gametes for genetic diversity.

Binary Fission: Asexual reproduction in prokaryotes; produces genetically identical cells.
Mitosis: Division in eukaryotes for growth, maintenance, and asexual reproduction; produces genetically identical cells.
Meiosis: Division in eukaryotes for sexual reproduction; produces genetically unique gametes.

Binary fission is the primary method of reproduction in prokaryotes, such as bacteria.

Single, Circular Chromosome: Prokaryotes possess one chromosome attached to the plasma membrane.
DNA Replication: The chromosome is duplicated, and each copy attaches to the membrane.
Cell Growth: The cell increases in size, separating the chromosomes.
Membrane and Cell Wall Growth: The plasma membrane and cell wall grow inward between the chromosomes.
Formation of Daughter Cells: Two genetically identical cells are produced.

The cell cycle describes the sequence of events in the life of a cell, culminating in cell division.

Interphase: The period between cell divisions, consisting of:
- G1 Phase: Cell growth and replication of organelles.
- S Phase: DNA synthesis and replication.
- G2 Phase: Continued growth and preparation for division.
- G0 Phase: A resting phase; cells may differentiate and are not preparing for division.
Cell Division: Includes mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Mitosis is the process by which a eukaryotic cell divides its nucleus, ensuring each daughter cell receives an identical set of chromosomes.

Prophase:
- Breakdown of the nuclear envelope.
- Condensation of chromosomes.
- Migration of centrioles and formation of spindle fibers.
- Spindle fibers attach to sister chromatids.
Metaphase:
- Chromosomes are aligned at the cell's midline (metaphase plate).
Anaphase:
- Sister chromatids are separated, becoming daughter chromosomes.
- Daughter chromosomes move toward opposite poles.
Telophase:
- Spindle fibers break down.
- DNA uncondenses.
- Nuclear envelope reforms around each set of chromosomes.

Cytokinesis is the final step in cell division, separating the cytoplasm into two daughter cells.

Animals: Formation of a cleavage furrow that pinches the cell in two.
Plants: Formation of a cell plate that develops into a new cell wall, separating the two cells.

Type	Organisms	Purpose	Genetic Outcome
Binary Fission	Prokaryotes	Asexual reproduction	Identical to parent
Mitosis	Eukaryotes	Growth, maintenance, asexual reproduction	Identical to parent
Meiosis	Eukaryotes	Sexual reproduction	Genetically unique

During binary fission, E. coli duplicates its single chromosome, grows in size, and divides into two identical daughter cells.

Human skin cells undergo mitosis to replace damaged or dead cells, maintaining tissue integrity.

Cell cycle checkpoints (not listed in the outline) regulate progression and ensure fidelity of division.
Errors in mitosis can lead to aneuploidy or cancer.