Lesson Objectives  Contrast cell division in prokaryotes and eukaryotes.  Identify the phases of the eukaryotic cell cycle.  Explain how the cell cycle is controlled.  Define cancer, and relate it to the cell cycle.  Describe chromosomes and their role in mitosis.  Outline the phases of mitosis.

 binary fission  cancer  cell cycle  cell division  cytokinesis  DNA replication  interphase  mitosis  Tumor  somatic  anaphase  centromere  chromatid  chromatin  chromosome  gene  homologous chromosomes  metaphase  prophase  telophase

 How does it differ between eukaryotes and prokaryotes?

 Most prokaryotic cells divide by the process of binary fission. Blue and red lines indicate old and newly- generated bacterial cell walls, respectively. Eventually the parent cell will pinch apart to form two identical daughter cells.

 Step 1: DNA Replication. Just before the cell divides, its DNA is copied. This results in two identical chromosomes instead of just one. This step is necessary so that when the cell divides, each daughter cell will have its own chromosome.  Step 2: Chromosome Segregation. The two chromosomes segregate, or separate, and move to opposite ends (known as poles) of the cell.  Step 3: Cytokinesis. A new plasma membrane starts growing into the center of the cell, and the cytoplasm splits apart, forming two daughter cells. The two daughter cells that result are genetically identical to each other and to the parent cell.

How do little elephants grow up to be BIG elephants?

MITOSIS

 To create two identical daughter cells that are genetically identical to the parent cell

Asexual Reproduction Mitosis Mitosis is the process in which the nucleus divides to form two new nuclei. How does mitosis differ in plants and animals?

 Somatic cells  (all body cells except gamete (sex) cells)

The process of asexual reproduction begins after a sperm fertilizes an egg. It starts with a zygote

Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun. Cell that reproduce by asexual reproduction reproduce constantly.

Animated Cell Cycle Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis Mitosis

Growth Phase 1/G1 phase- (cell growth) Cell increases in size and makes more proteins and organelles Synthesis Phase/S phase- (DNA Replication) number doubles Growth Phase 2/G2 phase- (preparing for cell division) organelles need for cell division

Animal Cell Plant Cell Photographs from:

Genetic material inside the nucleus begins to condense and the duplicated chromosomes are visible in the form of chromatids. Spindle fibers begin to form outside the nucleus between centrioles which move to opposite ends of the cell At the end of prophase, the nucleolous and nuclear membrane disappear

Animal Cell Plant Cell Photographs from: Spindle fibers Centrioles

Chromatids (or pairs of chromosomes) attach to the spindle fibers at the centromeres and line up in the middle of the cell.

Animal Cell Plant Cell Photographs from:

Chromatids separate and begin to move to opposite ends of the cell as individual chromosomes when spindle fibers shorten.

Animal Cell Plant Cell Photographs from:

Chromosomes begin to uncoil and form chromatin Nuclear envelope reforms around each group of chromatin Spindle fibers begin to break apart Animal Cell begins to “pinch” called a cleavage furrow

Animal Cell Plant Cell Photographs from:

Division of the cytoplasm In animal cells the cell membrane moves inward creating a clevage furrow, pinching all the way through, creating two daughter cells – each with its own nucleus with identical genetic code. In plant cells, a cell plate forms along the equator of the parent cell. Then, a new plasma membrane and cell wall form along each side of the cell plate.

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 If the cell cycle occurred without regulation, cells might go from one phase to the next before they were ready.  What controls the cell cycle? How does the cell know when to grow, synthesize DNA, and divide?  The cell cycle is controlled mainly by regulatory proteins, cyclin. These proteins control the cycle by signaling the cell to either start or delay the next phase of the cycle. They ensure that the cell completes the previous phase before moving on. Regulatory proteins control the cell cycle at key checkpoints, which are shown in Figure to the right. There are a number of main checkpoints.

Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

I Interphase P Prophase M Metaphase A Anaphase T Telophase C Cytokinesis IPMATC I Play M ore At T he Carnival

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38 - Cell Division 38

Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell’s DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor (see Figure below). The rapidly dividing cells take up nutrients and space that normal cells need. This can damage tissues and organs and eventually lead to death.below These cells are cancer cells, growing out of control and forming a tumor.

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 Cell division is part of the life cycle of virtually all cells. It is a more complicated process in eukaryotic than prokaryotic cells because eukaryotic cells have multiple chromosomes and a nucleus.  The cell cycle is a repeating series of events that cells go through. It includes growth, DNA synthesis, and cell division. In eukaryotic cells, there are two growth phases, and cell division includes mitosis.  The cell cycle is controlled by regulatory proteins at three key checkpoints in the cycle. The proteins signal the cell to either start or delay the next phase of the cycle.  Cancer is a disease that occurs when the cell cycle is no longer regulated. Cancer cells grow rapidly and may form a mass of abnormal cells called a tumor.