Cell Division in Eukaryotes: Mitosis

Eukaryotic Chromosomes Composed of chromatin: complex of DNA and proteins Chromosome number varies in species Humans have 46 (23 identical pairs) Drosophila has 8 (4 identical pairs)

Eukaryotic Chromosomes Telomere: specialized structure that caps the end of each chromosome Centromere: contains repeated DNA sequences that bind specific proteins; make up the kinetochore where the microtubules bind during cell division Microtubules: composed of the protein tubulin; moves the chromosomes into position for cell division Kinetochore

Eukaryotic Cell Cycle Requires the duplication of the genome, segregation, and division of cellular contents Divided into 5 phases, which can be grouped into two based on functions

Interphase: Preparation for Mitosis Gap Phase 1: (G1) primary growth phase, usually the longest phase “Gap phase” refers to gap between cytokinesis and DNA synthesis Synthesis: (S) cell synthesizes a replica of the genome Gap Phase 2: (G2) secondary growth phase Fills in gap between DNA synthesis and start of mitosis Mitochondria and other organelles replicate while microtubules begin to assemble at a spindle

Interphase Gap Phase 0: (G0) resting state after G1, may remain in this state for days to years Muscle and nerve cells remain in G0 permanently Most of the cells in an animal’s body are in G0 at any given time

Interphase

P (prophase) M (metaphase) A (anaphase) T (telophase) C (cytokinesis) Mitosis: “M Phase” Chromosome Segregation and Division of Cytoplasmic Contents P (prophase) M (metaphase) A (anaphase) T (telophase) C (cytokinesis)

Prophase: chromosomes condense and become visible while the nuclear envelope breaks down; the spindle begins to assemble P

Metaphase: microtubules become organized into a spindle, attach to chromosomes from opposite poles, and move them to the equatorial plane M

Anaphase: initiated by sister chromatids separating – daughter chromosomes move to opposite poles of the cell and spindle poles move apart A

Telophase: chromosomes cluster at opposite poles and decondense while nuclear envelopes re-form around them T

C Cytokinesis: not technically mitosis, but part of the “M phase” Involves cleavage of cell at cleavage furrow into roughly equal halves C (cleavage furrow)

Recap Interphase M Phase G1 G0 S G2 Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Mitosis