How Cells Divide

Bacterial Cell Division Bacteria divide by binary fission. the single, circular bacterial chromosome is replicated Occurs in the NUCLEOID region Clonal- offspring cell is identical to parent cell

Eukaryotic Chromosomes -linear chromsomes -every species has a different number of chromosomes -composed of chromatin – a complex of DNA (40%) and proteins (histones) (60%)

Eukaryotic Chromosomes Karyotype: the particular array of chromosomes of an organism Chromosomes vary in Size Staining properties Location of centromere Length of arms

Eukaryotic Cell Cycle The eukaryotic cell cycle has 5 main phases: 1. G1 (gap phase 1) 2. S (synthesis) 3. G2 (gap phase 2) 4. M (mitosis) 5. C (cytokinesis) G0 (resting phase) The length of a complete cell cycle varies greatly among cell types. Interphase

Time proportions for each cycle

Interphase Interphase is composed of: G1 (gap phase 1) S phase time of cell growth Usually longest phase S phase synthesis of DNA (DNA replication) 2 sister chromatids are produced G2 (gap phase 2) chromosomes condense, growth, organelles replicate, spindle assembles

Mitosis Mitosis is divided into 5 phases: 1. Prophase 2. Prometaphase 4. Anaphase 5. Telophase

Mitosis Prophase: Chromosomes continue to condense and first become visible Centrioles move to each pole of the cell Spindle apparatus is assembled Spindles form between centrioles Nuclear envelope dissolves ER re-absorbs its components

Mitosis Prometaphase: Nondisjunction can occur Chromosomes become attached to the spindle apparatus Sister chromatids are connected to opposite poles of the spindle Microtubules begin to pull each chromosome toward the center of the cell Nondisjunction can occur

Mitosis Metaphase: Karyotyping Microtubules pull the chromosomes to align them at the center of the cell, equidistant from both poles Metaphase plate: imaginary plane through the center of the cell where the chromosomes align Chromosomes are most condensed here Karyotyping

Mitosis Anaphase: Microtubules pull sister chromatids toward the poles In anaphase A, sister chromatids are pulled apart towards poles In anaphase B the poles move apart Cell becomes visibly elongated Shortest phase

Mitosis Telophase: Spindle apparatus disassembles Tubules broken down which will be used to create cytoskeleton of daughter cells Nuclear envelope forms around each set of sister chromatids Chromosomes begin to uncoil Uncoiling permits gene expression Nucleolus reappears in each new nucleus

Cytokinesis Cytokinesis – cleavage of the cell into equal halves In animal cells –cleavage furrow In plant cells –cell plate Organelles go with whatever side of the cell they happen to be on As long as there are a few organelles on either side, the cell can make more