MITOSIS 11915 Mitosis In eukaryotic cells both the

MITOSIS 11/9/15

Mitosis In eukaryotic cells, both the cytoplasm and the nucleus divide to produce to identical daughter cells. Mitosis occurs in both unicellular and multicellular organisms. Cells have the same number of chromosomes as the original cell. Unicellular = one original cell is transformed into two identical cells. Multicellular = mitosis results in the addition of cells to a tissue or organ. Remember the phases of mitosis: prophase, metaphase, and telophase.

The Cell Cycle The cell cycle is the repeating set of events that make up the life of a cell. Mitosis is one phase of the cycle. The time between cell division is called interphase.

Interphase Cells spend most of their lifetime in interphase. Khan Academy Video There are three phases: 1. G 1 phase – cells grow to mature size. 2. S phase - DNA is copied. 3. G 2 phase – cells prepare for cell division.

G 0 Phase Cells can exit the cell cycle (usually after G 1) and enter G 0 phase. During G 0 phase, cells do not copy their DNA and do not prepare for cell division. Many cells in the human body are in this phase. Example: Cells of the nervous system.

Prophase The first TRUE phase of mitosis. Why? Begins with the formation of chromosomes. The chromatin thickens and coils around proteins. The nuclear membrane and nucleolus disappear, and the centrosomes appear. Spindle fibers appear and form the mitotic spindle.

Centrosomes Centrosomes are a pair of dark spots that appear as the nucleus disappears. In animal cells, each centrosome contains a pair of small, cylinder-shaped bodies called centrioles. In both plants and animals, the centrosomes begin to move to opposite sides (poles) of the cell.

Mitotic Spindle As the centrosomes separate, spindle fibers made of microtubules form the mitotic spindle. The mitotic spindle serves move the chromosomes and equally divide them among the two offspring cells. The spindle attaches to the centrosomes, one on each end.

Types of Spindle Fibers 1. 2. Kinetichore fibers – attach to each chromatid at the centromere (to a protein called the kinetichore) Polar fibers – extend across the dividing cell from centrosome to centrosome.

Chromosome Anatomy The centromere holds the two copies together. Each copy is called a chromatid. As long as the chromatids are attached to a centromere they are regarded as chromosomes.

Metaphase The chromosomes line up single file down the center of the cell. The kinetochore fibers move the chromosomes into position. FYI: karyotypes are typically made from pictures of chromosomes in metaphase.

Anaphase The chromatids separate at the centromere and move slowly toward opposite ends of the cell. At this point, the chromatids become individual chromosomes.

Telophase The spindle fibers disassemble and the chromosomes return to chromatin. A nuclear envelope forms around each set of chromosomes. A nucleolus forms in each new nucleus. Cytokinesis occurs.

Cytokinesis in Animal Cells Cytokinesis is the division of the cytoplasm. It begins with a pinching inward of the cell membrane. Eventually, this area becomes a cleavage furrow that separates the dividing cell into two cells.

Cytokinesis in Plant Cells In plant cells, vesicles formed by the Golgi apparatus fuse at the midline, forming the cell plate. When complete, the cell plate separates the cell in to two cells.

The Result of Mitosis Offspring cells receive: An identical copy of the original cell’s chromosomes. Approximately one-half of the original cell’s cytoplasm and organelles.

Prokaryotes vs. Eukaryotes Remember all cells come from other cells, and cell division is the process by which cells produce offspring cells. Just as the chromosome structure in prokaryotes and eukaryotes differs, cell division differs in prokaryotes and eukaryotes. Prokaryotes divide by binary fission. Eukaryotes divide by mitosis.

Binary Fission Remember, prokaryotic cells have NO NUCLEUS. They have one ring shaped chromosome that attaches to the cell membrane. Binary fission has three stages: 1. 2. 3. DNA is copied. Cell grows to twice its normal size. The cell divides by forming a cell wall between the two chromosomes.

Binary Fission in Prokaryotes