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Chapter 4 Cell Structure and Function Including some materials from lectures by Gregory Ahearn University of North Florida Ammended by John Crocker Copyright © 2009 Pearson Education, Inc.. What Is the Cell Theory? Tenets of Modern Cell Theory • Every living organism is made of one or more cells • The smallest organisms are made of single cells while multicellular organisms are made of many cells • All cells arise from pre-existing cells Copyright © 2009 Pearson Education Inc. 4.1 What Features Are Shared By All Cells? Cells are the smallest unit of life. Cells are enclosed by a plasma membrane. Cells use DNA as a hereditary blueprint. Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region. Cells obtain energy and nutrients from their environment. Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. 4.1 What Features Are Shared By All Cells? Cell function limits cell size. • Most cells are small (1 to 100 um in diameter) • Cells need to exchange nutrients and wastes with the environment • No part of the cell can be far away from the external environment. • Diffusion of molecules across cell membranes limits the diameter of cells. • As cells get bigger, their nutrient and waste elimination needs grow faster than the membrane area to accommodate them. Copyright © 2009 Pearson Education Inc. 4.1 What Features Are Shared By All Cells? The volume of cytoplasm grows faster than the plasma membrane area. Fig. 4-2 Copyright © 2009 Pearson Education Inc. tallest trees 10 m 1m 10 cm 1 cm adult human visible with unaided human eye Relative sizes Diameter 100 m chicken egg frog embryo 100 m 10 m 1 m Units of measurement: 1 meter (m) = 39.37 inches 1 centimeter (cm) = 1/100 m 1 millimeter (mm) = 1/1,000 m 1 micrometer (m) = 1/1,000,000 m 1 nanometer (nm) = 1/1,000,000,000 m 10 nm 1 nm 0.1 nm visible with special electron microscopes 100 nm most eukaryotic cells visible with conventional electron microscope visible with light microscope 1 mm mitochondrion most bacteria virus proteins diameter of DNA double helix atoms Fig. 4-1 Copyright © 2009 Pearson Education Inc. All Cells Share Common Features A plasma membrane encloses all cells and regulates material flow Cytoplasm is the fluid interior where a cell’s metabolic reactions occur • May contain organelles • Fluid portion (cytosol) contains water, salts, and organic molecules Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. All Cells Share Common Features All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint All cells use RNA (ribonucleic acid) to copy DNA to make proteins All cells obtain energy and nutrients from the environment All cells use common building blocks to build the molecules of life Copyright © 2009 Pearson Education Inc. Some Cell Types Have Cell Walls Cell walls are stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists • • Composed of polysaccharides like cellulose or chitin Support and protect fragile cells and are usually porous Copyright © 2009 Pearson Education Inc. Cell Walls Cell walls in plants may have multiple layers • • • Primary cell walls in plants are outermost Secondary cell walls are innermost Cell walls of adjacent cells joined by middle lamellae Copyright © 2009 Pearson Education Inc. 4.2 How Do Prokaryotic And Eukaryotic Cells Differ? There are two kinds of cells. • Prokaryotic cells • Are found only in two groups of single-celled organisms—the bacteria and archaea • Eukaryotic cells • Are structurally more complex cells • Possess a membrane-enclosed nucleus • Probably arose from prokaryotic cells Copyright © 2009 Pearson Education Inc. There Are Two Basic Cell Types Prokaryotic • Before nucleus Copyright © 2009 Pearson Education Inc. 4.7 What Are The Features Of Prokaryotic Cells? Prokaryotic cells are much smaller than eukaryotic cells (< 5 µm long) Are very reproductively successful and so are more abundant Have a simple internal structure Surrounded by a stiff cell wall, which provides shape and protection Can take the shape of rods, spheres, or helices Copyright © 2009 Pearson Education Inc. Prokaryotic Cells No nuclear membrane or membrane-bound organelles are present Some have internal membranes used to capture light Cytoplasm contains ribosomes used for protein synthesis Cytoplasm may contain food granules Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Prokaryotic Cells Single, circular chromosome of DNA • Chromosome found coiled in an area called the nucleoid Small rings of DNA (plasmids) are located in the cytoplasm Copyright © 2009 Pearson Education Inc. Prokaryotic Cells Some bacteria are propelled by flagella Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces Pili and fimbriae are protein projections in some bacteria that further enhance adhesion Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. There Are Two Basic Cell Types Eukaryotic • True nucleus • Includes Protist, Fungi, Plant, and Animal cells Copyright © 2009 Pearson Education Inc. 4.3 What Are The Main Features Of Eukaryotic Cells? Eukaryotic cells are > 10 µm long The cytoskeleton provides shape and organization A variety of membrane-enclosed organelles perform specific functions Copyright © 2009 Pearson Education Inc. Major Features Nucleus: contains DNA Mitochondria: produce energy Endoplasmic reticulum: synthesizes membrane components and lipids Golgi apparatus: molecule sorting center Lysosomes: digest cellular membranes or defective organelles Microtubules: make up the cytoskeleton Copyright © 2009 Pearson Education Inc. Major Features A generalized animal cell flagellum cytoplasm rough endoplasmic reticulum ribosome lysosome nuclear pore chromatin (DNA) nucleus nucleolus nuclear envelope centriole intermediate filaments plasma membrane Golgi apparatus vesicle microtubules free ribosome smooth endoplasmic reticulum Copyright © 2009 Pearson Education Inc. vesicle mitochondrion Fig. 4-3 Major Features Animal and plant cells differ with regards to cell walls, chloroplasts, plastids, central vacuoles, and centrioles Copyright © 2009 Pearson Education Inc. Major Features A generalized plant cell microtubules (part of cytoskeleton) mitochondrion chloroplast central vacuole Golgi apparatus plasmodesma smooth endoplasmic reticulum vesicle cell wall rough endoplasmic reticulum plasma membrane nucleolus nuclear pore chromatin nuclear envelope intermediate filaments nucleus ribosomes free ribosome Fig. 4-4 Copyright © 2009 Pearson Education Inc. 4.4 What Role Does The Nucleus Play? The nucleus is the largest organelle in the cell. • It is bounded by a nuclear envelope. • It contains granular-looking chromatin. • It contains the nucleolus. Copyright © 2009 Pearson Education Inc. The Nucleus The nuclear envelope separates chromosomes from cytoplasm • Envelope is a double membrane with nuclear pores for transport • Some smaller materials can move through the pores, while others, such as DNA, are excluded. • Outer membrane is studded with ribosomes Copyright © 2009 Pearson Education Inc. The Nucleus The nucleus nuclear envelope nucleolus nuclear pores nucleus nuclear pores chromatin (a) Structure of the nucleus (b) Yeast cell Fig. 4-5 Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. The Nucleus The nucleus contains DNA in various configurations • Compacted chromosomes (during cell division) • Diffuse chromatin (as DNA directs reactions through an RNA intermediate by coding for proteins) Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. The Nucleus Darker area within the nucleus called the nucleolus • Functions as the site of ribosome synthesis • Ribosomes synthesize proteins • Ribosomes are composed of RNA and proteins Copyright © 2009 Pearson Education Inc. The Nucleus Ribosome components are made at the nucleolus. • The nucleolus contains DNA, RNA, proteins, and ribosomes in various stages of construction. • This is the site where components of ribosomes are constructed. • Ribosome components leave the nucleus and are assembled in the cytoplasm. Copyright © 2009 Pearson Education Inc. 4.5 What Roles Do Membranes Play In Eukaryotic Cells? The plasma membrane isolates the cell, and alternately, helps it interact with its environment. • The phospholipid bilayer contains globular proteins that regulate the transport of molecules into and out of the cell. • Plant, fungi, and some protist cells also have a cell wall outside the plasma membrane, which acts as a protective coating. Copyright © 2009 Pearson Education Inc. System of Membranes The endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell • There are two forms of ER: • Rough endoplasmic reticulum: is studded with ribosomes • Smooth endoplasmic reticulum: has no ribosomes Copyright © 2009 Pearson Education Inc. System of Membranes Smooth ER has no ribosomes • Contains enzymes that detoxify drugs (in liver cells) • Synthesizes phospholipids and cholesterol. • Together with rough ER are the sites of new membrane synthesis for the cell. Copyright © 2009 Pearson Education Inc. System of Membranes Rough ER is studded with ribosomes on outside • Produces proteins and phospholipids destined for other membranes or for secretion (export) • Together with rough ER are the sites of new membrane synthesis for the cell. Copyright © 2009 Pearson Education Inc. System of Membranes Vesicles are membranous sacs that transport substances among the separate regions of the membrane system Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. System of Membranes The Golgi Apparatus is a set of stacked flattened sacs • Receive proteins from ER (via transport vesicles) and sorts them by destination • Modify some molecules (e.g. proteins to glycoproteins) • Package material into vesicles for transport Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. System of Membranes Three fates of substances made in the membrane system: 1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane – The following figure illustrates this process for antibodies – Antibodies are proteins produced by white blood cells to inactivate foreign diseasecausing agents Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. System of Membranes 2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell • Lysosomes fuse with food vacuoles and digest food into basic nutrients • In the cytoplasm, they digest defective organelles or pieces of membrane into component parts that can be recycled. Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. System of Membranes 3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Vacuoles Mitochondria Chloroplasts Plastids Cytoskeleton Cilia and flagella Copyright © 2009 Pearson Education Inc. Vacuoles Fluid-filled sacs with a single membrane Functions of vacuoles • Contractile vacuoles in freshwater organisms used to collect and pump water out • Many plant cells have a large central vacuole. • Plant central vacuoles used in several ways • Maintain water balance • Store hazardous wastes, nutrients, or pigments • Provide turgor pressure on cytoplasm to keep cells rigid Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Mitochondria Extract Food Energy Mitochondria are round, oval, or tubular sacs of double-membranes • Inner membrane is folded into cristae • Intermembrane compartment lies between inner and outer membranes • Matrix space within inner membrane Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Mitochondria Extract Food Energy Function as the “powerhouses of the cell” • Mitochondria extract energy from food molecules • Extracted energy is stored in high-energy bonds of ATP • Energy extraction process involves anaerobic and aerobic reactions Copyright © 2009 Pearson Education Inc. Mitochondria Extract Food Energy Mitochondria may be remnants of free-living prokaryotes (endosymbiotic hypothesis) Copyright © 2009 Pearson Education Inc. Chloroplasts Chloroplasts are specialized organelles surrounded by a double membrane • Outer membrane • Inner membrane encloses the stroma space • Stacked hollow membranous sacs (grana) within stroma are called thylakoids • The thylakoid membranes contain chlorophyll and other pigments that capture sunlight and with CO2 and water make sugar and O2 (photosynthesis) Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Plants Use Plastids for Storage Plastids found only in plants and photosynthetic protists Surrounded by a double membrane Functions • • Storage for photosynthetic products like starch Storage of pigment molecules giving color to ripe fruit Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Cytoskeleton The cytoskeleton provides shape, support, and movement. • All organelles in the cell do not float about the cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton. Several type of protein fibers make up the cytoskeleton. • Microfilaments: thin fibers • Intermediate filaments: medium-sized fibers • Microtubules: thick fibers Copyright © 2009 Pearson Education Inc. Cytoskeleton plasma membrane microfilaments mitochondrion microtubules (red) intermediate filaments ribosomes endoplasmic reticulum microtubule nucleus vesicle microfilaments (blue) (a) Components of the cytoskeleton (b) Cell with stained cytoskeleton Fig. 4-9 Copyright © 2009 Pearson Education Inc. Cilia and Flagella Cilia and flagella are extensions of the plasma membrane Cilia and flagella are composed of microtubules in a “9+2” arrangement formed by centrioles which become membrane-anchored structures called basal bodies Cilia are short (10-25 µm) and numerous while flagella are long (50-75 µm) but few in any cell Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Cilia and Flagella Long pairs of microtubules slide along each other (using ATP) causing movement of cilia and flagella Functions • Cilia or flagella may be used to move cell about • Cilia may be used to create currents of moving fluid in their environment Copyright © 2009 Pearson Education Inc. 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Cilia provide force parallel to the plasma membrane, which can be described as a “rowing” motion. propulsion of fluid power stroke plasma membrane return stroke cilia lining the trachea (a) Cilium Fig. 4-10a Copyright © 2009 Pearson Education Inc. 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat. direction of locomotion propulsion of fluid continuous propulsion flagellum of human sperm (b) Flagellum Fig. 4-10b Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Evolution of Membrane-Enclosed Organelles The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis) Copyright © 2009 Pearson Education Inc. Evolution of Mitochondria Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest Predatory cell and bacterium gradually enter into a symbiotic relationship Descendants of engulfed bacterium evolve into mitochondria Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Evolution of Chloroplasts Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium Predatory cell and bacterium gradually enter into a symbiotic relationship Descendants of engulfed bacterium evolve into chloroplasts Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Evidence for Endosymbionts Many biochemical features are shared by eukaryotic organelles and living bacteria Mitochondria, chloroplasts, and centrioles contain their own supply of DNA Living intermediates (modern cells that host bacterial endosymbionts) • Pelomyxa palustris harbors aerobic bacteria • Paramecium harbors photosynthetic bacteria Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc.