Cell Cycle: Cell Growth & Cell Division (PDF)

# The Cell Cycle: Cell Growth & Cell Division ## Biology is the only subject in which multiplication is the same thing as division. * The image shows a cell dividing into two daughter cells. * The process of cell division is essential for growth, repair and reproduction. ## The Cell Cycle - The c...

# The Cell Cycle: Cell Growth & Cell Division ## Biology is the only subject in which multiplication is the same thing as division. * The image shows a cell dividing into two daughter cells. * The process of cell division is essential for growth, repair and reproduction. ## The Cell Cycle - The cell cycle is a series of events that takes place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells. - The cell cycle consists of 3 main stages : * Interphase * The cell grows and copies its chromosomes. * This is the longest stage in the cell cycle. * Mitosis * The cell's nucleus divides. * The cell prepares for division. * Cytokinesis * The cell's cytoplasm divides. * The cell's organelles are separated. ## Where it all began... - You started as a cell smaller than a period at the end of a sentence. ## And now look at you... - How did you get from there to here? ## Getting from there to here... - Going from egg to baby... the original fertilized egg has to divide... and divide... and divide... and divide... * An image shows the stages of an egg dividing into smaller cells. ## Why do cells divide? - For reproduction - Asexual reproduction - one-celled organisms - For growth - From fertilized egg to multi-celled organism - For repair & renewal - Replace cells that die from normal wear & tear or from injury * Images are shown of mitosis and cytokinesis in plant cells. * Images are shown of a starfish, amoeba and a lizard. ## 1) Reproduction - There are two types of cellular reproduction: * 1) Asexual reproduction - The process of producing offspring from only one parent. - Offspring are genetically identical to the parent. - Offspring are called clones, meaning that each is an exact copy of the original organism. - Examples: bacteria. * 2) Sexual reproduction - The process of producing offspring by the fusion of two gametes. - Gametes are sex cells that contain half of the DNA found in regular body cells. - Gametes for fertilization usually come from separate parents. - Female - produces an egg. - Male - produces sperm. - To produce gametes, cells must undergo *meiosis*, which results in haploid sex cells (half the number of *chromosomes*). * The image shows a sperm cell and an egg cell. ## 2) Growth - Multicellular organisms grow by increasing the number of cells. - In order for a cell to function properly, it cannot be too big as communication and movement within the cell would not be efficient. - Transporting substances in and out of the cell are necessary for cell growth, and are carried out by *diffusion* and *osmosis*. - *Diffusion* - Movement of substances into and out of a cell from an area of high concentration to an area of low concentration. - *Osmosis* - Diffusion of water across the cell membrane. * The image shows a cell membrane with molecules diffusing across. ## 3) Repair - When part of an organism is damaged, remaining cells divide to *repair* the injury. - Damaged cells will be replaced by new cells produced through cell division (*Mitosis*). * An image shows a lizard with a regrowing tail after autotomy. ## New organelle: Centrioles - The primary function of centrioles is in cell division. - In animal cells, a pair of centrioles organize spindle fibers to guide chromosomes during mitosis. * The image shows a pair of centrioles in a cell. ## Organizing DNA - DNA is organized in chromosomes. - Double helix DNA molecule wrapped/coiled around *histone* proteins. - *Chromatin* is a DNA-protein complex organized into long, thin fibers. - Condensed further during mitosis to become a chromosome. * An image shows the structure of DNA. The image shows the DNA molecule, histones, chromatin, and the double-stranded chromosome which is duplicated during mitosis. ## Chromosome structure: Folding of DNA - DNA double helix is wrapped around proteins. - The image shows a chromosome with the DNA double helix wrapped around histones. ## Overview of Mitosis - I.P.M.A.T.C. (Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis) - The image visually shows the stages of mitosis. ## Stages of the Cell Cycle - 3 main stages of cell cycle: - Interphase - Cell carries out normal functions, grows and makes copies of its genetic material. - Mitosis - Cell's nucleus and genetic material divide. - Cytokinesis - Begins near the end of *Mitosis*, involves division of cell cytoplasm and creation of a new cell. - All *somatic* cells (body cells/non-sex cells) undergo the cell cycle. ## The Cell Cycle - *Interphase* - S phase: *DNA* synthesis and replication. - G1 phase: rapid growth and cell activity. - G2 phase: cell prepares for division. - *Mitosis* and *cytokinesis*. * The image shows a pie chart illustrating the stages of the cell cycle. ## Interphase - Divided into 3 phases: G1, S, and G2 - G1 or Growth 1 - Major period of growth for a cell. - The cell is synthesizing new molecules to prepare for the next phase. * The image shows a pie chart highlighting the stages of interphase. ## Interphase - S or Synthesis - Cellular *DNA* is replicated. - *DNA* exists as uncondensed fibers called *chromatin*. - G2 or Growth 2 - Cell synthesizes more molecules prior to mitosis and cell division. - What it looks like: - Nucleus well-defined, *DNA* loosely packed in long *chromatin* fibers. * The image shows a cell in the G2 phase of interphase. ## Interphase - 90% of cell life cycle. - Cell doing its "everyday job". - Produces proteins and enzymes. - Prepares for duplication if triggered. * The image shows a pie chart with a cell labeled "I'm working here!" and another labeled "Time to divide & multiply!" ## Mitotic Chromosome - Duplicated chromosome - 2 sister chromatids. - Narrow at *centromeres*. - Contains identical copies of original *DNA*. * The image shows a duplicated chromosome with sister chromatids. * The image is divided into 3 sections: - Single-stranded homologous chromosomes - Double-stranded homologous chromosomes (sister chromatids). - Homologous chromosomes. ## Mitotic Human Chromosomes * The image shows a picture of double-stranded mitotic human chromosomes. The image is in black and white, with the chromosomes appearing as light gray shapes against a black background. ## Mitosis - Dividing cell’s *DNA* between 2 *daughter nuclei*. - "Dance of the chromosomes". - 4 phases: - Prophase - Metaphase - Anaphase - Telophase * The image features a cell in the telophase phase of mitosis. ## Prophase - *Chromatin* condenses - visible chromosomes. - Centrioles move to opposite poles of the cell. - *Spindle* fibers cross the cell to coordinate the movement of chromosomes. - Nucleolus disappears. - Nuclear envelope/membrane breaks down. * The image shows a cell in the prophase phase of mitosis. ## Metaphase - Spindle fibers attach to the *centromere* of each chromosome to guide them. - Chromosomes align along the middle of the cell, called the *equator* or *metaphase* plate. * The image shows a cell in the metaphase phase of mitosis. ## Anaphase - Chromosomes separate at the *centromere*. - Pulled and move to opposite poles by the *spindle* fibers. - Poles move farther apart. * The image shows a cell in the anaphase phase of mitosis. ## Telophase - Chromosomes arrive at opposite poles. - Daughter nuclei form. - Chromosomes unravel - no longer visible under a light microscope. - *Cytokinesis* begins - cell division. * The image shows a cell in the telophase phase of mitosis. ## Cytokinesis - Animals - Constriction belt around the *equator*. - *Cytoplasm* & organelles separate into roughly equal parts. - *Cleavage furrow* forms. - Splits the cell in two. - Like tightening a drawstring. * Animal cell cytokinesis: The cell divides into daughter cells when the *cleavage furrow* pinches off. * Plant cell cytokinesis: The cell divides into daughter cells when the *cell plate* forms. * The image shows a cell during cytokinesis. ## Mitosis in whitefish blastula * The image shows a series of six pictures of a whitefish blastula. The cell division process is shown in each image, with the cell going through the stages: - Interphase - Prophase - Metaphase - Anaphase - Early telophase - Late telophase ## Mitosis in animal cells * The image shows six pictures of a cell in different stages of mitosis in an animal cell: - G2 Interphase - Prophase - Prometaphase - Metaphase - Anaphase - Telophase ## Cytokinesis in Plants - Plants - *Cell plate* forms. - New cell wall laid down between membranes. - New cell wall fuses with existing cell wall. * The image shows a cell during cytokinesis in a plant cell. ## Cytokinesis in plant cell * The image shows a cell during cytokinesis in a plant cell. ## Onion root tip * The image shows an onion root tip undergoing mitosis. Many cells are shown in different stages of the cell cycle. * The image is of a microscope slide viewed at a high magnification.