Cell Replication Today we are going to look at how cells replicate. Cell Theory tells us that all cells came from pre-existing cells. Without replication for growth, replacing damaged cells, or for cells that have just died life could not exist. An adult body contains about 100 trillion cells. Some cells rarely replicate (liver, nerve, heart, muscle, brain).

Prokaryotes Most Prokaryotes (single cell without nucleus) reproduce Asexually through a process called Binary Fission. The Prokaryote replicates it’s DNA ring and organelles and just splits in half so that each half gets a complete identical copy of the DNA. Bacteria and many other single cell Protist reproduce this way and huge number of cells can be produced this way quickly.

Bacteria and Organelles

Binary Fission Bacteria

Binary Fission Paramecium and Amoeba

Eukaryotes Cell division is more complicated than in Prokaryotes. For a Eukaryotic cell to divide it must go through the cell cycle: mitosis for somatic cells and meiosis for sex cells.

Cell Cycle Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase G 1 The normal growth time for a cell as it progresses toward DNA replication. S This is the time that DNA is replicated prior to going into mitosis. Once DNA is duplicated growth continues for a short time. G 2 The cell continues to grow and prepare for Mitosis to begin. DNA checked for errors. A process called APOPTOSIS kills the cell if the DNA is not reproduced correctly.

Interphase 85% to 90% of the cells life is spent in interphase. Nerve cells and muscle cells spend their whole life in interphase. Liver cells rarely divide.

Mitosis vs. Meiosis Mitosis uses asexual reproduction to create new somatic cells (body cells) for growth, replacement worn out or damaged cells, and reproduces 2 identical daughter cells. The resulting cell is diploid (46 chromosomes just like the mother cell). Meiosis uses sexual reproduction to create new sex cells (sperm or egg). Used to create 4 haploid ( gametes) sex cells each having 23 chromosomes. This is where genetic variation is introduced.

Mitosis The process where somatic cells actually split and create two “identical daughter cells.” Creating two daughter cells is the total reason for a cell go through mitosis. It has four steps: Prophase, Metaphase, Anaphase, and Telophase. PMAT

Prophase Is the first step of mitosis. 1. The nuclear envelope begins to disappear. 2. Chromosomes begin to condense. 3. Centrioles begin to move to opposite sides of the cell.

Metaphase Is the second step of mitosis. 1.The chromosomes line up at the center of the cell. 2.Spindle fibers form from the centrioles and attach to the chromosomes at the centromere. 3.Most easily recognized stage.

Anaphase Is the third step in mitosis. 1.The centrioles begin to pull the spindle fibers toward the opposite sides of the cell. 2. Chromosomes split ensuring the exact DNA on either side of the cell.

Telophase Is the fourth phase of mitosis. 1.The nuclear envelope begins to reappear. 2.The cell begins to pinch in the center in preparation for separation. 3.Chromosomes begin to unwind in the nucleus.

Mitosis Mitosis ends at the end of Telophase.

Cytokinesis The cells actually divide and begin to function as two completely identical cells beginning the G 1 step of the Cell Cycle. Two identical cells is the result of mitosis.

Cytokinesis In animal cells the cell is basically “pinched in half” where a cell furrow is created by the dividing cytoplasm. In plant cells the cell is separated by growth of a cell plate that separates the dividing cytoplasm.

Cell plate vs Cell Furrow

Plant or Animal Cell?

31 MitosisMeiosis Number of divisions 12 Number of reproduced cells 24 Genetically identical? YesNo Chromosome # Same as parent Half of parent Where Somatic cells Sex cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction Comparison of Divisions

Tumor The uncontrolled division of a somatic cell. This is why cancer is such a hard disease for doctors to cure; Uncontrolled cell division