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Chapter 4 A Tour of the Cell PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Art of Looking at Cells • Artists have long found inspiration in the visual richness of the living world • Conversely, scientists use art to illuminate their findings – Micrographs show structures as scientists see them – Drawings can emphasize details Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings INTRODUCTION TO THE CELL 4.1 Microscopes provide windows to the world of the cell • A light microscope (LM) enables us to see the overall shape and structure of a cell – Passes visible light through a specimen – Can study living cells and cells and tissues that have been stained – Can magnify only about 1,000 times Video: Euglena Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-1a Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source • Magnification is the increase in the apparent size of an object; for example, 1,000X Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Resolution is a measure of the clarity of an image – A light microscope can resolve objects as small as 2 m Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The electron microscope (EM) allows greater magnification than LM and reveals cellular details – Uses a beam of electrons rather than light – Has much greater resolution than LM (2 nm) – Can magnify up to 100,000 times – Cannot be used with living specimens Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Scanning electron microscope (SEM) studies detailed architecture of cell surfaces Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Transmission electron microscope (TEM) studies the details of internal cell structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Modifications to LM use different techniques to enhance contrast and selectively highlight cellular components Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4.2 Most cells are microscopic • Cells vary in size and shape – Minimum is determined by the total size of all the molecules required for cellular activity – Maximum is limited by the need for sufficient surface area to carry out functions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-2a Human height Length of some nerve and muscle cells Chicken egg Frog egg Most plant and animal cells Nucleus Most bacteria Mitochondrion Mycoplasmas (smallest bacteria) Viruses Ribosome Proteins Lipids Small molecules Atoms • A small cell has a greater ratio of surface area to volume than a large cell of the same shape • The microscopic size of most cells ensures a sufficient surface area across which nutrients and wastes can move to service the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-2b 10 m 30 m 30 m Surface area of one large cube = 5,400 m2 10 m Total surface area of 27 small cubes = 16,200 m2 4.3 Prokaryotic cells are structurally simpler than eukaryotic cells • There are two kinds of cells – Prokaryotic (bacteria, archaea) – Eukaryotic (protists, plants, fungi, animals) • All cells share some common features – Plasma membrane – DNA – ribosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-3a Prokaryotic cell Nucleoid region Nucleus Organelles Eukaryotic cell • Prokaryotic cells – Usually relatively small, relatively simple cells • Do not have a membrane-bound nucleus • DNA is coiled into a nucleoid region in the cytoplasm • Cytoplasm includes ribosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Other prokaryotic structures – Plasma membrane – Complex cell wall – Capsule, pili, prokaryotic flagella in some forms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-3b Prokaryotic flagella Ribosomes Capsule Cell wall Plasma membrane Nucleoid region (DNA) Pili 4.4 Eukaryotic cells are partitioned into functional compartments • Eukaryotic cells are usually larger than prokaryotic cells (10-100 (m diameter) – Distinguished by a true nucleus – Contain both membranous and nonmembranous organelles • Compartmentalize metabolism • Increase membrane surface area for reactions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Animal cells – Are bounded by the plasma membrane alone – Lack a cell wall – Contain centrioles and lysosomes – Often have flagella Video: Cytoplasmic Streaming Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-4a Rough endoplasmic reticulum Smooth endoplasmic reticulum Nucleus Flagellum Not in most plant cells Lycosome Centriole Ribosomes Peroxisome Microtubule Cytoskeleton Intermediate filament Microfilament Golgi apparatus Plasma membrane Mitochondrion • Plant cells – Are bounded by both a plasma membrane and a rigid cellulose cell wall – Have a central vacuole and chloroplasts – Usually lack centrioles, lysosomes, and flagella Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-4b Nucleus Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum Golgi apparatus Microtubule Central vacuole Not in animal Chloroplast cells Cell wall Mitochondrion Peroxisome Plasma membrane Intermediate filament Microfilament Cytoskeleton ORGANELLES OF THE ENDOMEMBRANE SYSTEM 4.5 The nucleus is the cell's genetic control center • The nucleus contains the cell's DNA – Controls cellular activities by directing protein synthesis – Forms long fibers of chromatin that make up chromosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The nucleus is separated from the cytoplasm by the nuclear envelope – Pores in the envelope control flow of materials in and out – Ribosomes are synthesized in the nucleolus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-5 Nucleus Chromatin Nucleolus Two membranes of nuclear envelope Pore Rough endoplasmic reticulum Ribosomes 4.6 Overview: Many cell organelles are connected through the endomembrane system • The endomembrane system is a collection of membranous organelles – Divide the cell into compartments – Work together in the synthesis, storage, and export of molecules • Prime example: Endoplasmic reticulum (ER) – A continuous network of flattened sacs and tubes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4.7 Smooth endoplasmic reticulum has a variety of functions • Smooth endoplasmic reticulum (smooth ER) lacks attached ribosomes – Synthesizes lipids – Processes materials such as toxins and drugs in liver cells – Stores and releases calcium ions in muscle cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-7 Smooth ER Rough ER Nuclear envelope Ribosomes Rough ER TEM 45,000 Smooth ER 4.8 Rough endoplasmic reticulum makes membrane and proteins • Rough endoplasmic reticulum (rough ER) is studded with ribosomes – Manufactures membranes – Modifies and packages proteins that will be • Transported to other organelles • Secreted by the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-8 Transport vesicle buds off Secretary (glyco-) protein inside transport vesicle Ribosome Sugar chain Glycoprotein Polypeptide Rough ER 4.9 The Golgi apparatus finishes, sorts, and ships cell products • The Golgi apparatus consists of stacks of flattened membranous sacs – Receives and modifies substances manufactured by ER – Ships modified products to other organelles or the cell surface Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-9 Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming “Shipping” side of Golgi apparatus Transport vesicle from the Golgi Golgi apparatus 4.10 Lysosomes are digestive compartments within a cell • Lysosomes are sacs of enzymes that form from the Golgi apparatus – Function in digestion within a cell – Destroy bacteria that have been ingested into white blood cells – Recycle damaged organelles Animation: Lysosome Formation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-10a Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus Engulfment of particle Lysosome engulfing damaged organelle “Food” Lysosomes Food vacuole Digestion LE 4-10b Lysosome TEM 8,500 Nucleus LE 4-10c Mitochondrion fragment Peroxisome fragment TEM 42,500 Lysosome containing two damaged organelles CONNECTION 4.11 Abnormal lysosomes can cause fatal diseases • Lysosomal storage diseases – Result from an inherited lack of one or more lysosomal enzymes – Seriously interfere with various cellular functions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4.12 Vacuoles function in the general maintenance of the cell • Plant cells contain a large central vacuole – Has lysosomal and storage functions • Some protists have contractile vacuoles – Pump excess water out of cell Video: Paramecium Vacuole Video: Chlamydomonas Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-12a Nucleus Colorized TEM 8,700 Chloroplast Central vacuole LE 4-12b Contractile vacuoles LM 650 Nucleus 4.13 A review of the endomembrane system • The various organelles of the endomembrane system are interconnected structurally and functionally Animation: Endomembrane System Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-13 Rough ER Transport vesicle from ER to Golgi Transport vesicle from Golgi to plasma membrane Plasma membrane Nucleus Vacuole Lysosome Smooth ER Nuclear envelope Golgi apparatus ENERGY-CONVERTING ORGANELLES 4.14 Chloroplasts convert solar energy to chemical energy • Chloroplasts are found in plants and some protists – Are the site of photosynthesis – Have a complex membranous structure for capturing and converting light energy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-14 Stroma Chloroplast Granum Intermembrane space TEM 9,750 Inner and outer membranes 4.15 Mitochondria harvest chemical energy from food • Mitochondria are found in nearly all eukaryotic cells – Divided into two membranous compartments • Intermembrane space • Second compartment enclosed by inner membrane – Contains fluid mitochondrial matrix – Membrane folded into cristae Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Carry out cellular respiration • Convert the chemical energy in food to ATP for cellular work Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-15 Mitochondrion Outer membrane Intermembrane space Cristae Matrix TEM 44,880 Inner membrane THE CYTOSKELETON AND RELATED STRUCTURES 4.16 The cell's internal skeleton helps organize its structure and activities • The cytoskeleton is network of three types of protein fibers – Microfilaments • Rods of globular proteins • Enable cells to change shape and move Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Intermediate filaments • Ropes of fibrous proteins • Reinforce the cell and anchor certain organelles – Microtubules • Hollow tubes of globular proteins • Give the cell rigidity • Anchor organelles and act as tracks for organelle movement Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-16 Tubulin subunit Actin subunit Fibrous subunit 25 nm 7 nm Microfilament 10 nm Intermediate filament Microtubule 4.17 Cilia and flagella move when microtubules bend • Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells – Move whole cells or materials across the cell surface Video: Paramecium Cilia Animation: Cilia and Flagella Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The structure and mechanism of cilia and flagella are similar – Microtubules wrapped in an extension of the plasma membrane • 9 + 2 arrangement • Extend into basal bodies • Movement of dynein arms produces microtubule bending Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-17c Flagellum Electron micrographs of cross sections: TEM 206,500 Outer microtubule doublet Central microtubules Radial spoke Dynein arms Flagellum Basal body (structurally identical to centriole) TEM 206,500 Plasma membrane Basal body CELL SURFACES AND JUNCTIONS 4.18 Cell surfaces protect, support, and join cells • Cells interact with their environments and each other via their surfaces • Many cells are protected by more than the plasma membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Plant cell walls – Made largely of cellulose – Provide protection and support – Connect by plasmodesmata, channels through the wall Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-18a Walls of two adjacent plant cells Vacuole Plasmodesmata Layers of one plant cell wall Cytoplasm Plasma membrane • Animal cells – Embedded in an extracellular matrix that binds cells together in tissues – Connect by cell junctions • Tight junctions bind cells into leakproof sheets • Anchoring junctions link cells into strong tissues • Gap junctions allow substances to flow from cell to cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 4-18b Tight junctions Anchoring junction Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells Animation: Tight Junctions Animation: Desmosomes Animation: Gap Junctions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings FUNCTIONAL CATEGORIES OF ORGANELLES 4.19 Eukaryotic organelles comprise four functional categories • Eukaryotic organelles fall into four functional categories that work together to produce the cell's emergent properties – Manufacturing – Breakdown – Energy processing – Support, movement, and communication between cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings