MITOTIC PHASE ALTERNATES WITH INTERPHASE IN THE CELL CYCLE Chapter 12 section 2

TERMS TO KNOW  Chromatid- Each of a pair of identical DNA molecules after DNA replication, joined at the centromere.  Chromatin- Protein/DNA complex making the chromosome.  Chromosomes- Molecules of DNA complex with specific proteins responsible in eukaryotes for storage and transmission of genetic information.  Kinetochore- Structure forming at centromere during Mitosis for binding microtubules.

THE CELL CYCLE

PHASES OF THE CELL CYCLE  The mitotic (M) phase of the cell cycle alternates with the much longer interphase.  The M phase includes mitosis and cytokinesis.  Interphase accounts for 90% of the cell cycle.  During interphase, the cell grows by producing proteins and cytoplasmic organelles, copies its chromosomes, and prepares for cell division.

INTERPHASE!!!  Interphase has three subphases: the G1 phase (“first gap”), the S phase (“synthesis”), and the G2 phase (“second gap”).  During all three subphases, the cell grows by producing proteins and cytoplasmic organelles  However, chromosomes are duplicated only during the S phase.

MITOSIS  Produces two identical daughter cells  Has 5 different stages: Prophase, prometaphase, metaphase, anaphase, and telophase.  Cytokinesis is somewhat a part of mitosis, but differs depending on the type of cell - begins immediately following telophase

BREAKDOWN OF MITOSIS

PROPHASE  In prophase, the chromosomes are tightly coiled, with sister chromatids joined together.  The nucleoli disappear.  The mitotic spindle begins to form.  It is composed of centrosomes and the microtubules that extend from them.  The centrosomes move away from each other, apparently propelled by lengthening microtubules.

PROMETAPHASE AND METAPHASE  Nuclear membrane dissipates  Proteins attach to the centrosomes, creating the kinetochores.  Microtubules attach to kinetochores  Chromosomes begin moving and the spindle fibers align them in the middle.

ANAPHASE  The chromosomes separate at the kinetochores.  They move to opposites side of the cell.  Typically the shortest phase of mitosis

TELOPHASE  Chromatids are at the opposite sides.  New membranes form around the daughter nuclei.  Chromosomes disperse and spindle fibers disperse.  Cytokinesis will start to begin.

CYTOKINESIS  Animal cells: forms a cleavage furrow, which pinches the cell in two. This is caused by a fiber ring composed of a protein called actin around the center of the cell contracts.  Plant cells: a cell plate is synthesized between the two cells, which is produced by vesicles that are from the Golgi apparatus.

ANIMATION  MitosisFlash.html MitosisFlash.html

THE MITOTIC SPINDLE  The major driving force in mitosis.  It is fibers composed of microtubules and associated proteins.  The spindle assembles during prophase  Assembly of the spindle microtubules starts in the centrosome, which organizes the cell’s microtubules.

BINARY FISSION  Prokaryotes reproduce by binary fission.  In binary fission, chromosome replication begins at one point in the circular chromosome, the origin of replication site, producing two origins.  As the chromosome continues to replicate, one origin moves toward each end of the cell.  While the chromosome is replicating, the cell elongates.  When replication is complete, its plasma membrane grows inward to divide the parent cell into two daughter cells, each with a complete genome.

THE EVOLUTION OF MITOSIS (BINARY FISSION?!?!?)  Scientists believe that mitosis had its origins in binary fission.  Some of the proteins involved are in both binary fission and mitosis, which two of them are related to actin and tubulin.  As eukaryotes evolved, the process of binary fission gave rise to mitosis.

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