2.3 – The Importance of Cell Division Cells undergo cell division for reproduction, growth, and repair Cell Division for Reproduction Reproduction involves the transfer of genetic information from the parent(s) to the offspring. There are two types of reproduction Sexual reproduction the process of producing offspring by the fusion of two gametes; the production of offspring that have genetic information from each parent Asexual reproduction the process of producing offspring from only one parent; the production of offspring that are genetically identical to the parent

Cell Division for Growth As multicellular organisms grow, their cells duplicate their genetic information and divide. Plant and animal cells need a source of energy, nutrients, water and gases. They also need to excrete carbon dioxide and other waste materials. Chemicals diffuse into, throughout, and out of cells. This process must happen quickly enough for the cell to function properly. This is why the cell divides to form more cells instead of getting larger when it grows Cell Division for Repair When part of an organism is damaged, the remaining cells divide to repair the injury

The Cell Cycle Cells follow a cell cycle that includes growth and preparation for division (interphase) followed by cell division (mitosis and cytokinesis).

Cell Division Cell division occurs in two stages: mitosis (the division of the contents of the nucleus) and cytokinesis (the division of the rest of the cell, such as cytoplasm, organelles, and cell membrane).

Interphase Cells appear inactive but this is the longest period of the cell cycle. The cell continues to carry out growth and cellular respiration. In the Interphase stage: DNA replicates The centrioles divide Proteins are actively produced At the end of interphase, the spindle fibres form Microtubules of the cytoskeleton are responsible for cell shape, motility and attachment to other cells (The building blocks of these microtubules are used to grow the mitotic spindle from the region of the centrosomes.)

Prophase The first stage of mitosis The nucleolus fades Chromatin (replicated DNA and associated proteins) condenses into chromosomes. Each replicated chromosome comprises two chromatids, both with the same genetic information. Microtubules disassemble.

Prophase The chromosomes (containing DNA) become visible. Each chromosome consists of two identical strands called sister chromatids. The sister chromatids are held together by a centromere. The spindle fibres attach to the centromeres of each chromosome. The nuclear membrane dissolves.

Metaphase Tension applied by the spindle fibers aligns all chromosomes in one plane at the center of the cell

Metaphase The chromosomes line up in the middle of the cell. The spindle fibres apply tension to the chromosomes aligning them into the centre of the cell

Anaphase Spindle fibers shorten, the kinetochores separate, and the chromatids (daughter chromosomes) are pulled apart and begin moving to the cell poles.

Anaphase The centromere splits. The sister chromatids separate into daughter chromosomes. The spindles fibres pull each daughter chromosome towards opposite ends of the cell

Telophase The daughter chromosomes arrive at the poles and the spindle fibers that have pulled them apart disappear

Telophase Is the final phase of mitosis The daughter chromosomes (chromatids) stretch out and become invisible. A new nuclear membrane forms around each group of daughter chromosomes. The cell appears to have two nuclei

Cytokinesis The spindle fibers not attached to chromosomes begin breaking down until only that portion of overlap is left. It is in this region that a contractile ring cleaves the cell into two daughter cells. Microtubules then reorganize into a new cytoskeleton for the return to interphase

Cytokinesis Mitosis is followed by cytokinesis, which results in the entire cell dividing into two new daughter cells. Animal cell cytokinesis features the cell pinching off to form two daughter cells. Plant cell cytokinesis features a new cell wall forming to separate the two daughter cells.

Checkpoints in the Cell Cycle specialized proteins monitor cell activities and the cell’s surroundings these proteins send messages to the nucleus which then instructs the cell whether to divide or not A cell should remain in interphase and not divide if signals from surrounding cells tell the cell not to divide there are not enough nutrients to provide for cell growth the DNA within the nucleus has not been replicated the DNA is damaged

Mitosis Mitosis is the division of the nucleus into two identical nuclei. Mitosis has four phases: prophase, metaphase, anaphase, and telophase (PMAT).

Stages of Mitosis http://www.cellsalive.com/mitosis.htm