SNC 2DI THE CELL CYCLE I-PMAT-C

Why is cell division important? 1) Healing and tissue repair  Healing cuts, broken bones, replacing dead cells 2) Growth  Cell division allows an organism to grow bigger (from one cell to two cells to many cells eventually!) 3) Reproduction of organisms  Unicellular organisms like bacteria reproduce by dividing in two. Sexual reproduction in multicellular organisms occurs when sperm and egg cells are made from the division of cells in reproductive organs

If a Cell becomes too large: ◦ Nutrients from outside the cell can’t get to all parts of the cell quickly ◦ Messages from the nucleus take too long to travel to all cell parts ◦ Larger cells have less surface area (SA) than multiple cells of equal volume. Therefore, the larger cells cannot obtain enough nutrients from the surrounding environment

 Environment: sunlight, altitude  Antibiotics: inhibit cell growth and mitosis  DNA mutations – can disrupt apoptosis (the natural death of cells). This happens in Cancerous cells as an example. FACTORS THAT AFFECT CELL DIVISION

Mitosis (M) and Cytokinesis Rapid Cell Growth (G1) DNA Synthesis (S) Growth and Preparation for Cell Division (G2) Interphase Mitosis

Every hour, about one billion (10 9 ) cells die and are replaced in your body. Cells do not constantly divide. They go through periods of growth and preparing for cell division. This sequence of events is called the cell cycle. When cells are not dividing, they are in a stage (that has three sections) called interphase. During the first section this phase, cells go through a period of rapid growth, where they take in nutrients (like sugars) and produce new proteins and organelles. The cell spends 90% of its time in interphase.

Once the cell has grown to a size where its surface area is too small to service the large volume, the cell is unable to absorb enough substances or expel enough waste. At this point it is healthier for the cell to divide into two identical daughter cells. In preparation for the MITOSIS (M-phase), the cell prepares for division by doubling its chromosomes creating two identical copies of DNA called sister chromatids. Chromosomes must be duplicated because they contain very important information about how a cell functions, and each new cell will need a copy of this information. The nucleus divides in a process called mitosis and the cytoplasm and the rest of the cell divide through a process called cytokinesis.

The cell grows and carries out its normal functions. It then prepares for cell division by duplicating its DNA. -cell is in a resting phase -technically not part of mitosis, but it is included in the cell cycle -performing cell functions -DNA replicates (copies) -organelles double in number, to prepare for division

 When a cell is "resting" i.e. not dividing, the chromosomes are organized into an entangled structure called chromatin

In prophase, the chromatin condenses into discrete, double chromosomes.chromatin The nuclear envelope breaks down spindles form at opposite "poles" of the cell (IN ANIMAL CELLS) from the centrioles

The double-stranded chromosomes line up in the middle of the cell

Each chromosome splits. The two strands move away from each other to opposite poles of the cell

The chromosomes reach the opposite poles of the cell and a nuclear membrane begins to form around each set Cytoplasm and its contents are split into two equal parts. Cell membrane pinches to form two daughter cells.

 In this last stage, two distinct daughter cells are formed after the chomatids have migrated to the opposite poles. Cytokinesis is also occurring at this time.

 Cyto =cell  Kinesis=movement  The cell’s cytoplasm divides at the end of telophase  Animals - cell pinches inward  Plants - a new cell wall forms between the new cells

Mitosis results in two new cells that are identical to each other and to the parent cell. New cells enter G1/interphase.