WarmUp Word Bank Ligase Helicase Replication Fork Leading
Warm-Up Word Bank: Ligase, Helicase, Replication Fork, Leading Strand, Lagging Strand, Okazaki Fragments, DNA Polymerase Without looking at your notes, what is… a. b. c. d. e. f. g. e a b d c g g f
Final Stage of Interphase G 2 › Organelle are doubled. › DNA starts to condense into chromosomes Now, before you learn about the process of mitosis, you need to learn about the structure of chromosomes and how DNA is prepared for efficient separation into two daughter cells.
Chromosomes You know that DNA carries genetic information in the form of chromosomes During most of a cell’s life, its chromosomes exist in the nucleus disorganized › This form is called chromatin When a cell is preparing to divide, a special protein called histone packages the chromatin into chromosomes
CHROMATID #2 CHROMATID #1 Structure of the Chromosome Centromere
Recap Define the following terms: › › › Chromosome Chromatin Chromatid Histone Centromere
Objectives: Cell Division & the Cell Cycle Identify and restate what the phases of the eukaryotic cell cycle are. Restate what happens in each stage of the cycle.
Why the Cell Reproduces There are three main reasons cells divide: 1. To help tissues and organs grow. › We continuously add cells as we grow to get bigger. 2. To replace cells. › As old cells die or cells get damaged new cells take their place in order to maintain health. › As the cell ages, it continues to grow. When it gets too big it need to be replaced to limit cell size. 3. To repair broken cells. › When cells get damaged due to trauma they need to be replaced.
The Cell Cycle The cell cycle is a repeating sequence of cellular growth and division during the life of a cell. Interactive Cell http: //www. exploratorium. edu /traits/cell_explorer. html
Eukaryotic Cell Cycle The cell cycle starts with a new cell When the cell is created it starts in interphase. Interphase During interphase, the cell is not dividing. It is living; growing, making proteins, metabolizing sugars and other nutrients, then duplicates its DNA and prepares to divide. Different types of cells spend different amounts of time in interphase dependent upon their roles in the body. Cells that divide often, such as skin cells, spend less time in interphase. › Their job is more for protection & produce a shield, not to produce proteins. Cells that divide seldom, such as nerve cells, spend most of their time in interphase. › Their job is more for relaying information. › Muscle and other tissue cells are in this category.
Eukaryotic Cell Cycle: Recap Interphase is broken down into 3 stages. Interphase First gap phase (G 1) = Gene Expression, a cell grows rapidly as the cell builds more organelles and makes proteins. Synthesis phase (S) = Replication, a cell’s DNA is replicated. For most organisms, this phase occupies the major portion of the cell’s life as the cell performs most “life” functions here (like transcription & translation… gene expression). Chromosomes are not duplicated yet so they appear as single linear molecules (I’s) At the end of the S phase, the cell’s nucleus has twice as much DNA as it did in the G 1 phase. Second gap phase (G 2) = Preparation for division, the cell continues to grow and prepares to divide. DNA starts to condense, organelle, such as mitochondria, are duplicated.
Interphase Cell Only the nucleolus is visible under a microscope. The DNA is all spread out.
Eukaryotic Cell Cycle Cell Division The rest of the cell cycle is dedicated to dividing the cell’s now-duplicated chromosomes and the cytoplasm. The process of dividing the nucleus into two daughter nuclei is called mitosis. The process of separating the organelles and the cytoplasm is called cytokinesis.
Stages of Mitosis Although mitosis, the division of the nucleus, is a continuous process, biologists can see consistent events throughout. Mitosis can be observed in four stages: › › Prophase Metaphase Anaphase Telophase
Stages of Mitosis Stage 1 Prophase 1. Chromosomes condense fully and become visible under a light microscope. 2. The nuclear membrane breaks down, or dissolves. 3. Outside the nucleus, a special structure called the spindle forms.
Prophase: Spindle Fiber › The role of the spindle is to organize the movement of chromosomes during mitosis. The spindle is made up of several protein spindle fibers. Cells have an organelle called the centrosome, which helps assemble the spindle. In animal cells, the centrosome includes a pair of centrioles. Each centriole is made up of nine triplets of microtubules arranged as a short, hollow tube. Before mitosis, the cell’s centrosome is duplicated. During prophase, the centrosomes move to opposite poles of the cell. This gives 4 centrioles C B F E D A
Observe the Structure of this Prophase Cell
Stages of Mitosis, continued Stage 2 Metaphase During metaphase, the chromosomes are packaged into their most condensed form. 1. The nuclear membrane is fully dissolved, and the condensed chromosomes move to the center of the cell and line up along the cell’s equator. 2. Spindle fibers link the centromere of each chromosome to the centrosomes at opposite poles. A cell is metaphase is easy to identify as the chromosomes are all in the middle.
Stages of Mitosis, continued Stage 3 Anaphase Once all of the chromosomes are lined up, 1. the spindle fibers shorten. The spindle fibers shorten by breaking down the microtubules bit by bit. 2. Sister chromatids are pulled toward opposite poles as the spindle fibers that are attached continue to shorten. Anaphase cells are also easy to identify as the chromatids are clearly moving away from each other.
Stages of Mitosis, continued Stage 4 Telophase 1. A nuclear envelope forms around the chromosomes at each pole of the cell. 2. Chromosomes, now at opposite poles, uncoil and change back to their original chromatin form. 3. The spindle dissolves and the spindle fibers break down and disappear. Mitosis is complete.
Cytokinesis As mitosis ends, cytokinesis begins. During cytokinesis, the cell membrane grows into the center of the cell and divides it into two daughter cells of equal size. Each daughter cell has about half of the parent’s cytoplasm and organelles. The end result of mitosis and cytokinesis is two genetically identical cells in place of the original cell.
Cytokinesis: Animal v Plant Cells Separating the Cytoplasm In animal cells ( and other cells that lack cell walls ), the cell is pinched in half by a belt of protein threads. In plant cells and other cells that have rigid cell walls, the cytoplasm is divided in a different way. In plants, cell division is accomplished by vesicles creating a large, membrane-bound cell wall called the cell plate.
Cytokinesis Continuing the Cell Cycle After cytokinesis is complete, each new daughter cell enters the G 1 stage of interphase. The daughter cells are about equal in size—about half the size of the original cell. The activity of each cell continues because each has its own DNA and organelles. A new cell cycle then begins for each new cell.
Overview of Cell Features in the Stages
Interphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm
Prophase Animal Cell Plant Cell Spindle fibers Centrioles Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm
Metaphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm
Anaphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm
Telophase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm
Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis
Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis
Cell Cycle 35
Pay attention to the colors of the chromosomes. The different colors represent the chromosomes that come form mom and dad. Notice how they get separated at the centromeres. Mitosis
Summary The life of a eukaryotic cell cycles through phases of growth, DNA replication, preparation for cell division, and division of the nucleus and cytoplasm. Mitosis is a continuous process that can be observed in four stages: prophase, metaphase, and telophase. During cytokinesis, the cell membrane grows into the center of the cell and divides it into two daughter cells of equal size. Each daughter cell has about half of the parent’s cytoplasm and organelles.
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