Cell Growth and Division

Cell division is needed for… 1. Growth – most organisms grow by producing more cells 2. Cell Replacement 3. Reproduction (asexual)

Cell division must occur because.. Cells cannot continue to grow indefinitely. There are two main reasons why they cannot: –1. A larger cell places more demands on its DNA. –2. A cell’s volume increases faster than its surface area. Thus, before the cell becomes too large, it divides.

Cell division is when a cell divides into two new daughter cells. Step one: Mitosis – division of the nucleus Step two: Cytokinesis – division of the cytoplasm

Cell division is controlled by several factors: 1. When cells come in contact with each other, they stop growing. 2. Internal regulators (p53 gene, cyclin) make sure the cell doesn’t divide until chromosomes have doubled. 3. External regulators are growth factors that stimulate or inhibit growth. –These prevent organ systems from interfering with each other during embryonic development.

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Cancer is uncontrolled cell growth. When cells lose control over growth, a tumor forms. There are many cause of cancer: –1. genetics –2. tobacco –3 UV light –4. Viral infection (i.e. HPV)

The Cell Cycle Cell Cycle – the series of events that cells go through as they grow and divide.

Interphase – time in-between cell divisions. –Includes G 1, S, and G 2 –Gap 1 (G 1 ) – normal growth and protein production Synthesis (S) – chromosomes (DNA) are copied Chromosomes double (humans - from 46 to 92). The doubled chromosomes are connected by a centromere. –Gap 2 (G 2 ) – duplicate organelles and molecules needed for cell division are made.

Phases of the Cell Cycle Mitosis – the division of the cell nucleus –Mitosis has 4 phases: ProphaseMetaphaseAnaphaseTelophaseIPMAT –Mitosis results in two genetically identical daughter cells.

Interphase Nucleus is still in tact and the nucleolus is visible. Includes G 1, S, and G 2

Prophase Chromatin condenses into chromosomes. Centrioles separate and spindle fibers form. The nucleus (envelope) and nucleolus break down (no longer visible).

Metaphase Chromosomes line up at the center of cell. Each chromosome is attached to a spindle fiber at the centromere.

Anaphase The sister chromatids are pulled apart (centromere splits) to opposite ends of the cell.

Telophase Nuclear membrane and nucleolus reform. Mitotic spindle disappears. Nuclear division is complete.

Cytokinesis Pinching of the cytoplasm, resulting in two genetically identical cells.