Cell Division. During interphase, a cell s DNA is in a loose form called. It condenses into tightly coiled structures called chromosomes during.

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1 Cell Division The is a cell s total DNA. Prokaryotes DNA is found mostly in a single called the and also in small circles called. Eukaryotes have several DNA double helices packaged into. During interphase, a cell s DNA is in a loose form called. It condenses into tightly coiled structures called chromosomes during. cells are body cells. Human somatic cells contain chromosomes. This means that if you take a cell from your skin or a cell from your eye or a cell from your muscle, etc., they contain 46 chromosomes. Cell division enables the genome of one somatic cell to be passed onto two cells. Mitosis (M phase) divides the and sister chromatids and is immediately followed by that divides the. Mitosis consists of,,, and. Mitosis / cytokinesis are what enable organisms to and develop. In the case of some organisms like an amoeba mitosis / cytokinesis creates an entire new organism. Mitosis / cytokinesis also allows for renewal. For example, when you your finger, mitosis / cytokinesis allows for the skin to heal over. Chromosome changes during the cell cycle. Chromosomes in somatic cells first make of themselves. So 46 chromosomes become during the phase of interphase. This number then gets reduced back to per cell when the cell divides into 2 new daughter cells in the phase of the cell cycle. The cell cycle describes the sequence of events that occurs during each phase of a cell s life. Cells spend most of their lives in. It is made up of (1 st ), (Synthesis of DNA), and (2 nd ).

2 During the G 1 phase cells: 1) 2) make and organelles. During the S phase cells: 1) grow, 2) make proteins and organelles, and 3) copy their (2 sister chromatids). During the G 2 phase cells 1) grow, 2) make proteins and organelles, and 3) make sure the cell is ready to enter into the phase. After the M phase, the cell cycle can either the cycle again or it can become (G 0 ). The phases of mitosis and the events characteristic of each phase: Early Prophase Chromatin condenses into 2 sister chromatids. disappears. apparatus starts to form (micro ) that extend from the and. Late Prophase / Prometaphase Nuclear breaks down. Microtubules attach to the of each sister chromatid to a protein structure called the. microtubules also form. Metaphase Spindle apparatus is. Sister chromatids line up at the metaphase / equator of the cell. Nonkinetochore microtubules Anaphase The sister chromatids and are now considered Chromosomes move towards poles. Telophase The cell elongates and begins to pinch Nuclear envelope. Nucleolus. Chromosomes start to loosen back into

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4 The spindle apparatus includes: - = Made up of a centriole pair (at a angle) and microtubules in a shape called an aster. Some of the aster s microtubules will elongate by adding more of the protein to them. -Non-kinetochore microtubules = attach to the kinetochores of the sister chromatids. They enable the entire cell to. -Kinetochore microtubules = attach to the kinetochores of the sister chromatids during / metaphase. Then they pull the sisters apart and as they get near the poles. -Centrioles = Found in cells only. They get replicated during. As the chromosomes move toward their respective poles their microtubules on the side to the chromosome. This breaks off pieces of the microtubules into small tubulin subunits. Cytokinesis differs in plants and animals. In animals, cytokinesis occurs by forming a - a groove in the cell near the old metaphase plate created by micro Plant cells build a. eukaryotes like algae, amoeba, paramecium, etc. also do cell division, but with some differences. For example, the membrane does not break down, yet the spindle apparatus forms. This is possibly an intermediate stage to the of mitosis. Only do mitosis. Bacteria / prokaryotes divide by fission. Bacteria their DNA, attach it to the membrane, the cell lengthens, and then the cell divides in two.

5 Chemical are needed to regulate the cell cycle. They act as and tell the cell to go or stop dividing. For example, cells only divide when a wound needs to be repaired. Q: Which cells divide frequently? Which do not divide in an adult? There are major checkpoints in the cell cycle found in G 1, G 2, and M phases. The checkpoint is the most important. It determines if a cell will get the go signal or be switched to an inactive / state. Now let s analyze how the G 2 checkpoint works, taking a cell from G 2 to mitosis. (cyclin-dependent kinases) are. They carry from ATP. G 1 Cdk Cdk + ATP + Being an enzyme, Cdk doesn t get up and it has an site where a specific molecule can bind. In order for Cdk to be it needs a protein called to bind to its active site. Cyclin gets its name because it / fluctuates its concentrations / gets broken down after G 2. G 2 Cdk Cyclin

6 When Cdk comes together with cyclin, this complex together is called (M-phase Promoting Factor). This activates the passage from the checkpoint into the phase. Once in mitosis, the phosphates break off of the MPF complex and are used to other reactions in mitosis like the breaking up of the nuclear. Then cyclin breaks and Cdk can be used over again. We just described the G 2 checkpoint. Be aware that similar checkpoints also exist at the other checkpoints. For example, the M-phase checkpoint is important to make sure that daughter cells each end up with copy of each chromosome. Q: Where in mitosis does the M-phase checkpoint occur? The checkpoints in the cell cycle are examples of factors that influence cell division. factors also tell a cell when to divide. For example, is a protein that some cells secrete externally. GF triggers neighboring cells to divide. is one type of growth factor. It is released from a component of blood called. When platelets release PDGF it causes connective tissue to divide and this allows to heal. Normally, cells exhibit inhibition. This means when cells get they stop dividing. Normal cells also exhibit. This means in order to divide, normal cells must be to something. Q: What is cancer?

7 Cancer cells divide and invade tissues. If and when cancerous cells stop dividing, it is often at points in the cell cycle (not ). In a laboratory situation, cancer cells can become. There is one cancerous cell line that has been dividing in a lab since! Compare this to normal cells that divide between times before they stop dividing, age, and die. Define the following terms: A) Tumor- B) Benign Tumor- C) Malignant Tumor- D) Metastasis- E) Available Treatments-