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Chapter 4 A View of the Cell Cell History • The microscope was invented in the 17th century • Using a microscope, Robert Hooke discovered cells in 1665 • All living things are made of cells (cell theory) Cell Theory • All cells come from preexisting cells • The cell is the basic unit of organization of organisms. • All organisms are made up of one or more cells. • The light microscope enables us to see the overall shape and structure of a cell Image seen by viewer Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source • Electron microscopes were invented in the 1950s • They use a beam of electrons instead of light • The greater resolving power of electron microscopes – allows greater magnification – reveals cellular details • Scanning electron microscope (SEM) • Scanning electron micrograph of cilia • Transmission electron microscope (TEM) • Transmission electron micrograph of cilia Cell sizes vary with their function • Below is a list of the most common units of length biologists use (metric) • Cell size and shape relate to function Cell Types • There are two kinds of cells: prokaryotic and eukaryotic • Prokaryotic cells are small, relatively simple cells – They do not have a nucleus • A prokaryotic cell is enclosed by a plasma membrane and is usually encased in a rigid cell wall – The cell wall may be covered by a sticky capsule Prokaryotic flagella Ribosomes Capsule Cell wall – Inside the cell are its DNA and other parts Plasma membrane Pili Nucleoid region (DNA) Eukaryotic cells are partitioned into functional compartments • All other life forms are made up of one or more eukaryotic cells • These are larger and more complex than prokaryotic cells • Eukaryotes are distinguished by the presence of a true nucleus • An animal cell Smooth endoplasmic reticulum Nucleus Rough endoplasmic reticulum Flagellum Not in most plant cells Lysosome Centriole Ribosomes Peroxisome Microtubule Cytoskeleton Intermediate filament Microfilament Golgi apparatus Plasma membrane Mitochondrion • The plasma membrane controls the cell’s contact with the environment • The cytoplasm contains organelles • Many organelles have membranes as boundaries – These compartmentalize the interior of the cell – This allows the cell to carry out a variety of activities simultaneously • A plant cell has some structures that an animal cell lacks: – Chloroplasts – A rigid cell wall Nucleus Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum Golgi apparatus Microtubule Not in animal cells Central vacuole Intermediate filament Chloroplast Microfilament Cell wall Mitochondrion Peroxisome Plasma membrane Cytoskeleton The nucleus is the cell’s genetic control center • The largest organelle is usually the nucleus • The nucleus is separated from the cytoplasm by the nuclear envelope • The nucleus is the cellular control center – It contains the DNA that directs the cell’s activities NUCLEUS Chromatin Nucleolus Two membranes of nuclear envelope Pore ROUGH ENDOPLASMIC RETICULUM Ribosomes •The endomembrane system is a collection of membranous organelles –These organelles manufacture and distribute cell products –The endomembrane system divides the cell into compartments –Endoplasmic reticulum (ER) is part of the endomembrane system Rough endoplasmic reticulum makes membrane and proteins • The rough ER manufactures membranes • Ribosomes on its surface produce proteins Transport vesicle buds off 4 Ribosome Sugar chain 1 Polypeptide 3 Secretory (glyco-) protein inside transport vesicle Glycoprotein 2 ROUGH ER • Smooth ER synthesizes lipids • In some cells, it regulates carbohydrate metabolism and breaks down toxins and drugs SMOOTH ER ROUGH ER Nuclear envelope Ribosomes SMOOTH ER ROUGH ER •The Golgi apparatus consists of stacks of membranous sacs –These receive and modify ER products, then send them on to other organelles or to the cell membrane • The Golgi apparatus Golgi apparatus Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming “Shipping” side of Golgi apparatus Transport vesicle from the Golgi Lysosomes digest the cell’s food and wastes LYSOSOME • Lysosomes are sacs of digestive enzymes budded off the Golgi Nucleus • Lysosomal enzymes – digest food – destroy bacteria – recycle damaged organelles – function in embryonic development in animals Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus Engulfment of particle Lysosome engulfing damaged organelle “Food” LYSOSOMES Food vacuole Digestion • Plant cells contain a large central vacuole – The vacuole has lysosomal and storage functions Central vacuole Nucleus • Protists may have contractile vacuoles – These pump out excess water Nucleus Contractile vacuoles ENERGY-CONVERTING ORGANELLES • Chloroplasts are found in plants and some protists • Chloroplasts convert solar energy to chemical energy in sugars Chloroplast Stroma Inner and outer membranes Granum Intermembrane space •Mitochondria carry out cellular respiration MITOCHONDRION –This process uses the chemical energy in food to make ATP for cellular work Outer membrane Intermembrane space Inner membrane Cristae Matrix THE CYTOSKELETON AND RELATED STRUCTURES The cell’s internal skeleton helps organize its structure and activities • A network of protein fibers makes up the cytoskeleton • Microfilaments of actin enable cells to change shape and move • Intermediate filaments reinforce the cell and anchor certain organelles • Microtubules – give the cell rigidity – provide anchors for organelles – act as tracks for organelle movement