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Chapter 7: Cell Structure and Function

b. Life Is Cellular c. The Discovery of the Cell d. Early Microscopes Around the mid-1600s, scientists began to use microscopes to observe living things. In 1665, Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material. He saw that it was made of thousands of tiny, empty chambers. He called those chambers cells because they reminded him of a monasterys tiny rooms, which are called cells. In Holland around the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things. The microscope revealed tiny living organisms that seemed to be everywhere. e. The Cell Theory Cells - collection of living matter enclosed by a barrier that separates the cell from its surroundings; basic unit of all forms of life The cell theory states: All living things are composed of cells. Cells are the basic units of structure and function in living things. New cells are produced from existing cells. f. Exploring the Cell g. A History of the Cell 1665 - Hooke publishes his book, Micrographia. 1674 - Leeuwenhoek observes tiny living organisms in drops of pond water through his simple microscope. 1838 - Schleiden concluded that all plants are made up of cells. 1839 - Schwann concluded that all animals are made up of cells. 1855 - Virchow proposes that all cells come from existing cells, completing the cell theory. h. Prokaryotes and Eukaryotes i. Prokaryotes Prokaryotic cells have genetic material that is not contained in a nucleus. j. Eukaryotes Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell. k. Eukaryotic Cell Structure

l. Comparing the Cell to a Factory Organelles - specialized structure that performs important cellular functions within a eukaryotic cell. Cytoplasm - portion of the cell outside the nucleus m. Nucleus The nucleus contains nearly all the cells DNA and with it the coded instructions for making proteins and other important molecules. Chromatin - granular material you can see in the nucleus. Chromosomes - contains genetic information that is passed from one generation of cells to another. Nucleolus - a small, dense region in the nuclei. n. Ribosomes Ribosomes are small particles of RNA and protein found throughout the cytoplasm. Proteins are assembled on ribosomes. o. Endoplasmic Reticulum The internal membrane system in eukaryotic cells are endoplasmic reticulum. The endoplasmic reticulum is the site where lipid components of the cell membrane are assembled, along with proteins and other materials that export from the cell. p. Golgi Apparatus Proteins produced in the rough ER move next into an organelle call the Golgi apparatus. The functions of the Golgi apparatus is to modify, sort, and package protiens and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell. q. Lysosomes Lysosomes are small organelles filled with enzymes. They are involved in breaking down organelles that have outlived their usefulness. They perform the vital function of removing junk that might otherwise accumulate and clutter up the cell r. Vacuoles Some kind of cells contain saclike structures called vacuoles, the store materials such as water, salts, proteins, and carbohydrates. In many plants cells there is a single, large central vacuole filled with liquid. The pressure of the central vacuole in these cells makes it possible for plants to support heavy structures such as leaves and flowers. Vacuoles can be found in some single-celled organisms and in some animals.

s. Mitochondria and Chloroplasts t. Mitochondria Mitochondria are organelles that convert the chemical energy stored in food into compounds that are more convenient for the cell to use. It is enclosed by two membranes - an outer membrane and an inner membrane. The inner membrane is folded up inside the organelle. One of the most interesting aspects of mitochondria is the way in which they are inherited. In humans, all or nearly all of our mitochondria come from the cytoplasm of the ovum, or egg cell. u. Chloroplasts Chloroplasts are organelles that capture energy from sunlight and convert it into chemical energy in a process call photosynthesis. Plants and some other organisms contain chloroplasts. It is the biological equivalents of solar power plants. Like mitochondria, it is surround by two membranes. Inside the organelle are large stacks of other membranes, which contain the green pigment chlorophyll. v. Organelle DNA Unlike other organelles that contain no DNA, chloroplasts and mitochondria contain their own genetic information in the form of small DNA molecules. Lynn Margulis, an American biologist, has suggested that the both are actually descendents of ancient prokaryotes. This idea was called the end symbiotic theory. w. Cytoskeleton Eukaryotic cells have a structure - the cytoskeleton - that helps support the cell. The cytoskeleton is a network of protein filaments that helps the cell to maintain its shape. The cytoskeleton is also involved in movement. Microfilaments and microtubules are two of the principal protein filaments that make up the cytoskeleton. x. Microfilaments Are threadlike structures made of protein called actin. They form extensive networks in some cells and produce a tough, flexible framework that supports the cell. It can also help the cell move. y. Microtubules Are hollow structures made of protein known as

tubulins. In many cells, they play critical roles in maintaining cell shape. It is also important in cell division, where they form a structure known as the mitotic spindle, which helps to separate chromosomes. Centrioles are located near the nucleus and help to organize cell division. (Not found in plant cells.)