KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

What does this tell us about normal cells? That normal cells are regulated. How do you think? In response to injury, infection, regular growth or development, maintenance.

Let’s bake some Cookies…….no, not really. What do you need to do if you want to easily make two batches of Toll House cookies? You double it! (Double the ingredients from the original recipe) Let’s think cells instead of cookies! What do you need for a successful cell division to take place? Complete set of DNA, organelles, cytoplasm, cell membrane, cell wall (if plant)

Important Word Meanings Synthesis – the combining of parts to make a whole Cycle – a repeating series of events Related to the Latin word cyclus that means circle Phase – means appearance Comes from the Greek word phasis each stage of Mitosis has a distinct appearance Stages – means stand Comes from the Latin word stand Think about stopping points or stands along a journey, or even a non-stop flight where you stop temporarily

The cell cycle has four main stages. The cell cycle is a regular pattern of growth, DNA replication, and cell division. Let’s do the diagram in your Power Notes, first.

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. Get out your Study Guide for this section. Gap 1 (G1): cell growth and size increase cells carry out normal functions cells copy organelles Cell spends most of time here (length varies by cell type) Critical checkpoint before it can move on to synthesis stage (all must be in order: adequate cell size, undamaged DNA, adequate nutrition, signals from other cells in place) Examples: Skeletal muscle cell that contracts to move joints, intestinal cell absorbing nutrients

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. 2. DNA synthesis (S) cells copy or replicate DNA that is in the nucleus (nuclear DNA) Remember the definition of synthesis – combining of parts to make a whole (think about those Toll House cookies) At end of S, the cell nucleus contains two complete sets of DNA

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. 3. Gap 2 (G2) Cells continue to carry out normal functions additional growth of cells occur Second critical checkpoint found here (all must be in order – have DNA and centrosome been copied successfully?)

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. 4. Mitosis (M) Two processes of cell division here: Mitosis - division of cell nucleus and contents Nuclear membrane dissolves, duplicated DNA condenses around proteins, separates and two new nuclei form Cytokinesis - division of cell cytoplasm Result is two daughter cells that are genetically identical to original parent cell Mitosis occurs only if the cell is large enough and the DNA is undamaged.

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Cells divide at different rates. Prokaryotic cells do not contain membrane bound organelles or a cytoskeleton, so they will divide faster or slower than eukaryotic cells? The rate our eukaryotic cells divide depends on our body’s needs. Human cells: S, G2 and M take about 12 hours. G1 length caries from cell type to cell type. Rate of cell division greater in embryos and children than adults Adult intestinal tract cells are replaced regularly because they are frequently used and replaced every few days. Other major organ cells only replace when injury or cell death occurs.

Cells divide at different rates. The rate of cell division varies with the need for those types of cells. Go back to your Power Notes here. Some cells are unlikely to divide (G0). Possibly neuron cells, but this is debated. Lymphocytes also, until an invader binds to a lymphocyte receptor.

Cell size is limited. Volume increases faster than surface area If cells were too small, they could not contain all of the organelles and molecules necessary for life. What would happen to cells with not enough mitochondria? If cells were too large, they could not move enough materials across the membrane surface. Remember, oxygen, nutrients and waste are moved across the cell membrane. To maintain a suitable size, cell growth and division must be coordinated. If a cell more than doubles itself prior to dividing, the daughter cells would be larger than the parent cell and the cell would be too large to survive.

Cell size is limited. Volume increases faster than surface area.

Surface area must allow for adequate exchange of materials. Cell growth is coordinated with division. Cells that must be large have unique shapes.