Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 12.2 The Mitotic Phase Alternates with Interphase in the Cell Cycle
The eukaryotic cell cycle alternates between a growth period called interphase and a division phase called the mitotic (M) phase. Mitosis and cytokinesis produce genetically identical daughter cells.
Overview of the Cell Cycle
The cell cycle includes interphase and the mitotic (M) phase
Interphase makes up ~90% of the cycle and has three stages:
G₁ phase: cell grows and performs normal functions
S phase: DNA is replicated
G₂ phase: preparation for division
M phase: includes mitosis (nuclear division) and cytokinesis (cytoplasm division)
Daughter cells may enter a new cycle or a non-dividing state (G₀)
Stages of Mitosis
Prophase
Chromatin condenses into visible chromosomes
Mitotic spindle begins to form; nucleolus disappears
Prometaphase
Nuclear envelope breaks down
Microtubules attach to kinetochores on chromosomes
Metaphase
Chromosomes align at the metaphase plate
Spindle fibers attach from both poles
Anaphase
Cohesins are cleaved
Sister chromatids separate and move toward opposite poles
Telophase
Two nuclei form; chromosomes decondense
Mitosis ends
Cytokinesis
Animal cells: cleavage furrow forms and pinches cell in two
Plant cells: vesicles form a cell plate that becomes the new cell wall
The Mitotic Spindle
Made of microtubules and proteins; forms from centrosomes
Includes kinetochore microtubules (pull chromatids) and nonkinetochore microtubules (elongate the cell)
Microtubules shorten during anaphase, pulling chromosomes toward poles
Motor proteins aid in movement; mechanisms vary among species
Binary Fission in Bacteria
Bacteria divide via binary fission (no mitosis)
Chromosome replicates from a specific origin
Origins move to opposite ends of the cell
Cell elongates and divides into two genetically identical cells
Process involves actin-like and tubulin-like proteins
Evolution of Mitosis
Mitosis may have evolved from bacterial binary fission
Some unicellular eukaryotes (e.g., dinoflagellates, diatoms) retain intermediate division mechanisms
These variations provide clues to the evolutionary transition from prokaryotic to eukaryotic division
In a Nutshell
The cell cycle alternates between interphase and the mitotic phase, ensuring accurate DNA replication and division. Mitosis distributes chromosomes precisely, while cytokinesis splits the cell. In prokaryotes, binary fission fulfills a similar role without mitosis.