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Biology Chapter 7: Cell Structure and Function I. 7-1 Life Is Cellular a. The Discovery of the Cell i. Because there were no instruments to make cells visible, the existence of cells was unknown for most of human history. ii. This changed with the invention of the microscope b. Early Microscopes i. In 1665, Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material. ii. Cork looked like thousands of tiny, empty chambers. iii. Hooke called these chambers “cells.” iv. Cells are the basic units of life. v. At the same time, Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things. vi. The microscope revealed a world of tiny living organisms c. What is the cell theory? Hooke’s Drawing of Cork Cells i. The Cell Theory: 1. In 1838 Matthias Schleiden concluded that all plants were made of cells. 2. In 1839, Theodor Schwann stated that all animals were made of cells 3. In 1855, Rudolph Virchow concluded that new cells were created only from division of existing cells. 4. These discoveries led to the cell theory. ii. The cell theory states: 1. All living things are composed of cells. 2. Cells are the basic units of structure and function in living things 3. New cells are produced from existing cells. d. Exploring the cell i. New technologies allow researchers to study the structure and movement of living cells in great detail. ii. Electron Microscopes 1. Electron microscopes reveal details 1000 times smaller than those visible in light microscopes. 2. Electron microscopy can be used to visualize only nonliving, preserved cells and tissues. iii. Transmission electron microscopes (TEMs) 1. Used to study cell structures and large protein molecules 2. Specimens must be cut into ultra-thin slices 1. iv. Scanning electron microscopes (SEMs) 1. Produce three-dimensional images of cells 2. Specimens do not have to be cut into thin slices v. Confocal Light microscopes 1. Confocal light microscopes scan cells with a laser beam. 2. This makes it possible to build threedimensional images of cells and their parts vi. Scanning Probe Microscopes 1. Scanning probe microscopes allow us to observe single atoms 2. Images are produced by tracing surfaces of samples with a fine probe e. Prokaryotes and Eukaryotes i. Cells come in a variety of shapes and sizes ii. All Cells: 1. are surrounded by a barrier called a cell membrane 2. at some point contain DNA iii. Cells are classified into two categories, depending on whether they contain a nucleus iv. The nucleus is a large membrane-enclosed structure that contains the cell’s genetic material in the form of DNA v. The nucleus controls many of the cell’s activities vi. Eukaryotes are cells that contain nuclei vii. Prokaryotes are cells that do not contain nuclei f. What are the characteristics of prokaryotes and Eukaryotes? i. Prokaryotes 1. Prokaryotic cells have genetic material that is not contained in a nucleus 2. Prokaryotes do not have membrane-bound organelles 3. Prokaryotic cells are generally smaller and simpler than eukaryotic cells. 4. Bacteria are prokaryotes. ii. Eukaryotes 1. Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell 2. Eukaryotic cells are generally larger and more complex than prokaryotic cells. 3. Eukaryotic cells generally contain dozens of structures and internal membranes 4. Many eukaryotic cells are highly specialized 5. Plants, animals, fungi, and protists are eukaryotes 2. 3. 4. 5. Biology II. 7-2 Eukaryotic Cell Structure: Comparing the Cell to a Factory a. Eukaryotic Cell Structures i. Structures within a eukaryotic cell that perform important cellular functions are known as organelles ii. Cell biologists divide the eukaryotic cell into two major parts: the nucleus and the cytoplasm iii. The cytoplasm is the portion of the cell outside the nucleus iv. Plant Cell 1. nucleolus 2. nucleus 3. smooth endoplasmic reticulum 4. rough endoplasmic reticulum 5. cell wall 6. cell membrane 7. chloroplast 8. vacuole 9. mitrochondrion 10. golgi apparatus 11. ribosome (attached) 12. ribosome (free) 13. nuclear envelope v. Animal cell 1. nucleolus 2. nucleus 3. nuclear envelope 4. rough endoplasmic reticulum 5. centrioles 6. mitrochondrion 7. golgi apparatus 8. ribosome (attached) 9. cell membrane 10. ribosome (free) 11. smooth endoplasmic reticulum b. What is the function of the nucleus? i. The nucleus is the control center of the cell ii. The nucleus contains nearly all the cell’s DNA and with it the coded instructions for making proteins and other important molecules iii. The nucleus is surrounded by a nuclear envelope composed of two membranes iv. The envelope is dotted with nuclear pores, which allow material to move in and out of the nucleus v. The granular material in the nucleus is called chromatin vi. Chromatin consists of DNA bound to protein vii. When a cell divides, chromatic condenses to form chromosomes c. d. e. f. viii. Chromosomes contain the genetic information that is passed on from one generation of cells to the next. ix. Most nuclei also contain a nucleolus 1. The nucleolus is where the assembly of ribosomes begins What is the function of the ribosomes? i. Ribosomes 1. One of the most important jobs carried out in the cell is making proteins 2. Proteins are assembled on ribosomes 3. Ribsomes are small particles of RNA and protein found throughout the cytoplasm 4. Ribosomes produce proteins by following coded instructions that come from the nucleus 5. Cells that are active in protein synthesis are often packed with ribosomes What is the function of then endoplasmic reticulum? i. Endoplasmic Reticulum 1. Eukaryotic cells contain an internal membrane system called the endoplasmic reticulum, or ER 2. The endoplasmic reticulum is where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell. 3. There are two types of ER – rough and smooth 4. The portion of the ER involved in protein synthesis is called rough endoplasmic reticulum, or rough ER 5. Ribosomes are found on the surface of rough ER 6. Rough ER is abundant in cells that produce large amounts of protein for export. 7. Smooth ER does not have ribosomes on its surface 8. Smooth ER contains collections of enzymes that perform specialized tasks, such as synthesis of membrane lipids and detoxification of drugs What is the function of the Golgi apparatus? i. Golgi Apparatus 1. Proteins produced in the rough ER move into the Golgi apparatus 2. The Golgi apparatus appears as a stack of closely apposed membranes 3. The Golgi apparatus modifies, sorts and packages proteins and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell 4. From the Golgi apparatus, proteins are then “shipped” to their final destinations throughout the cell or outside of the cell What is the function of Lysosomes? i. Lysosomes 1. Lysosomes are small organelles filled with enzymes g. h. i. j. 2. Lysosomes break down lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell 3. Lysosomes also break down organelles that have outlived their usefulness What is the function of vacuoles:? i. Vacuoles 1. Some cells contain saclike structures called vacuoles that store materials such as water, salts, proteins, and carbohydrates 2. In many plant cells there is a single, large central vacuole filled with liquid 3. The pressure of the central vacuole allows plants to support heavy structures such as leaves and flowers 4. Vacuoles are also found in some unicellular organisms and in some animals 5. The paramecium contains a contractile vacuole that pumps excess water out of the cell What is the function of the mitochondria? i. Nearly all eukaryotic cells contain mitochondria ii. Mitochondria convert the chemical energy stored in food into compounds that are more convenient for the cell to use. iii. Mitochondria are enclosed by two membranes – an outer membrane and an inner membrane iv. The inner membrane is folded up inside the organelle What is the function of chloroplasts? i. Plants and some other organisms contain chloroplasts ii. Chloroplasts capture energy from sunlight and convert it into chemical energy in a process called photosynthesis. iii. Chloroplasts are surrounded by two membranes iv. Chloroplasts contain the green pigment chlorophyll What are the functions of the cytoskeleton? i. Cytoskeleton 1. Eukaryotic cells are given their shape and internal organization by the cytoskeleton. 2. The cytoskeleton is a network of protein filaments that helps the cell to maintain its shape. The cytoskeleton is also involved in movement. 3. The cytoskeleton is make up of: a. Microfilaments i. Are threadlike structures made up of the protein actin ii. Form extensive networks in some cells iii. Produce a tough, flexible framework that supports the cell iv. Help some cells move b. Microtubules 1. 2. i. Microtubules are hollow structures made up of proteins known as tubulins. Microtubules: ii. Maintain cell shape iii. Are important in cell division iv. Build projections from the cell surface-cilia and flagella-that enable some cells to swim rapidly through liquids 4. In animals cells, structures known as centrioles are formed from tubulin. 5. Centrioles are located near the nucleus and help to organize cell division 3. 4. 5. In the nucleus of a cell, the DNA is usually visible as • a dense region called the nucleolus. • the nuclear envelope. • granular material called chromatin. • condensed bodies called chloroplasts. Two functions of vacuoles are storing materials and helping to • break down organelles. • assemble proteins. • maintain homeostasis. • make new organelles. Chloroplasts are found in the cells of • plants only. • plants and some other organisms. • all eukaryotes. • most prokaryotes. Which of the following is NOT a function of the Golgi apparatus? • synthesize proteins • modify proteins • sort proteins • package proteins Which of the following is a function of the cytoskeleton? • manufactures new cell organelles • assists in movement of some cells from one place to another • releases energy in cells • modifies, sorts, and packages proteins