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The Cell: An Overview Basic Features of Cell Structure and Function Cells are small and are visualized using a microscope Cells have a DNA-containing central region surrounded by cytoplasm Cells occur in prokaryotic an eukaryotic forms, each with distinctive structures and organization Cell Theory: Fundamental to Life All organisms are cellular Cell: the smallest unit of life Cells come only from preexisting cells Examples of Cells Fig. 5-2, p. 92 Animation: Overview of cells Units of Measure Fig. 5-3, p. 93 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Small molecules Atoms Proteins Lipids Viruses Mitochondria Ribosomes Smallest bacteria Most bacteria Most plant and animal cells Fish egg Bird egg Human height Electron microscope Light microscope Unaided human eye 0.1 nm 1 nm 10 nm 100 nm 1 m 10 m 100 m 7 1 mm 1 cm 0.1 m 1m 10 m Cell size Link Amazing cells Think/Pair/Share Why are cells small? Surface to Volume Ratios Fig. 5-5, p. 95 Microscopy Magnification Ratio between the size of an image produced by a microscope and its actual size Resolution Ability to observe two adjacent objects as distinct from one another Contrast How different one structure looks from another – enhanced by dyes 11 Microscopy 2 groups of microscopes based on source of illumination Light microscope • Uses light for illumination • Resolution 0.2 µm Electron microscope • Uses an electron beam • Resolution 2 nm 12 Bright field microscopy Fig. 5-4a, p. 94 Dark field microscopy Fig. 5-4b, p. 94 Phase-contrast microscopy Fig. 5-4c, p. 94 Electron microscope types Transmission Beam of electrons transmitted through sample Thin slices stained with heavy metals Some electrons are scattered while others pass through to form an image Scanning electron microscopy (TEM) electron microscopy (SEM) Sample coated with heavy metal Beam scans surface to make 3D image 16 Transmission electron microscopy (TEM) Fig. 5-4d, p. 94 Scanning electron microscopy (SEM) Fig. 5-4h, p. 94 All Cells Contain DNA All cells have a central region with DNA Stores hereditary information (connection to evolution) Genes are located on DNA Proteins replicate DNA and copy information to RNA Cytoplasm Cytoplasm Surrounds the central region Cytosol Aqueous solution of cell Organelles Small organized structures within cytosol Plasma Membrane Fig. 5-6, p. 95 Animation: Cell membranes Membranes Plasma Membrane Plasma Lipid membrane defines cytoplasm bilayer and proteins Hydrophobic Selective passage hydrophilic Internal external environment of cell different from Amazing Cells link Prokaryotes and Eukaryotes Prokaryotes No boundary membrane in central region Nucleoid Domains: Archaea and Bacteria Eukaryotes Boundary membrane in central region True nucleus Domain: Eukarya Prokaryotic Cells Prokaryotic cells have little or no internal membrane structure Prokaryotic Cell Structure Fig. 5-7, p. 97 Animation: Typical prokaryotic cell Prokaryotic Internal Structure Small, little to no membrane structure Cell wall & capsule Plasma membrane allows metabolism ATP in mitochondria and chloroplasts Evolution by endosymbiosis Prokaryotic Information Transfer Nucleiod Chromatin and chromosome Three domain system (Carl Woese) Ribosomes Only organelle in common with eukaryotes DNA messenger RNA amino acids and proteins Prokaryotic Mobility and Ecology Many prokaryotes have flagella Different from eukaryotic flagella Prokaryotes relatively simple Exploit all known habitats Vastly outnumber eukaryotes Cycling of biological elements Table 5-1a, p. 96 Table 5-1b, p. 96 Eukaryotic Cells Eukaryotic cells have a membraneenclosed nucleus and cytoplasmic organelles Nucleus contains much more DNA than the prokaryotic nucleoid Cytoplasm has endomembrane systems dividing cell into functional and structural components Eukaryotic cells Mitochondria are the powerhouses of the cell Microbodies carry out vital reactions that link metabolic pathways The cytoskeleton supports and moves cell structures Flagella and cilia are the propellers of eukaryotic cells Eukaryotic Cell Overview Domain Eukarya (true nucleus) Includes protists, fungi, plants and animals Eukaryotic plasma membrane function Regulate/recognize substances (immune system) Cell-to-cell binding Fungi, walls plants and many protists have cell Video link Typical Animal Cell Fig. 5-8a, p. 99 Electron Micrograph of Animal Cell Fig. 5-8b, p. 99 Animation: Common eukaryotic organelles Video link Typical Plant Cell Fig. 5-9a, p. 100 Electron Micrograph Plant Cell Fig. 5-9b, p. 100 Which of these organelles are absent in plant cells? 1. 2. 3. 4. Mitochondria Centrioles Peroxisomes All of the above 25% 1 25% 25% 2 3 25% 4 Eukaryotic Nucleus Nuclear envelope separates nucleus and cytoplasm Two membranes and nuclear pores Nucleoplasm within nuclear envelope Chromatin and chromosomes Nucleolus Genes for ribosomal RNA If you treat cells with radioactive UTP, where in the cell would you expect the greatest concentration of radioactivity within the first few minutes? 1. 2. 3. 4. Rough ER Nuclear matrix Cytoplasm Nucleolus 25% 1 25% 25% 2 3 25% 4 Nuclear Envelope Fig. 5-10, p. 101 Endomembrane System Endomembrane system Connects all membranes Synthesizes/ modifies membrane proteins Synthesizes lipids Detoxification Vesicles exchange membrane throughout endomembrane system ER, Golgi, nuclear envelope, lysosomes, vesicles, plasma membrane Endoplasmic Reticulum Endoplasmic Interconnected network of membrane with cisternae and lumen Rough reticulum (ER) ER Ribosomes bound to surface Membrane-associated protein synthesis Endoplasmic Reticulum Smooth ER No ribosomes Synthesizes lipids and detoxifies Proportion activities rough/smooth ER reflect cell Endoplasmic Reticulum Fig. 5-11, p. 102 b. Smooth ER ER lumen Cisternae (mitochondrion) Smooth ER lumen Fig. 5-11b, p. 102 Golgi Complex Golgi Between rough ER and plasma membrane Golgi complex stack of flattened sacs receives and modifies proteins Molecularly tags vesicles Vesicles perform many functions Exocytosis and endocytosis Golgi Complex Fig. 5-12, p. 103 Lysosomes Lysosomes Vesicles from Golgi complex Hydrolytic enzymes from ER; low pH Autophagy removes nonfunctional organelles Phagocytosis digests extracellular material Major function of immune systems Endocytosis, Exocytosis and Lysosomes Fig. 5-13-14, p. 104 Vesicle Traffic Fig. 5-15, p. 105 A membrane protein synthesized in the rough ER may be directed to 1. 2. 3. 4. Peroxisomes Lysosomes Mitochondria All of the above 25% 1 25% 25% 2 3 25% 4 Brefeldin A is a drug that disrupts transport from the ER to the Golgi apparatus. What other organelles and membranes are affected? 1. 2. 3. Lysosomes, vacuoles, plasma membrane Vacuoles, mitochondria, plasma membrane All organelles and membranes 100% 1 Mitochondria Cellular respiration yields ATP Mitochondria Outer membrane smooth Inner membrane folded (cristae) Mitochondrial matrix Mitochondria have two membranes have own genome Endosymbiosis Mitochondria Fig. 5-16, p. 106 Microbodies Microbodies Single membrane organelles Not part of endomembrane system Microbody enzymes link biochemical pathways Examples Peroxisomes, glyoxysomes or glycosomes Microbodies Fig. 5-17, p. 107 Cytoskeleton Cytoskeleton Maintains shape and organization Interconnected protein fibers and tubes Most prominent in animal cells Plants and fungi also use cell walls and central vacuole Cytoskeleton Network of three different types of protein filaments Microtubules Intermediate filaments Long, hollow cylindrical structures Dynamic instability Intermediate in size Form twisted, ropelike structure Actin filaments Also known as microfilaments Long, thin fibers 65 Cytoskeleton Examples Fig. 5-18, p. 107 Cytoskeleton Components Main elements of animal cytoskeletons Microtubules are supportive Intermediate fibers thinner, interconnected with microtubules Microfilaments thinnest 68 Cytoskeleton Components Each element assembled from proteins Microtubules from tubulin Intermediate fibers from intermediate filaments Microfilaments from actins Major Components of Cytoskeleton Fig. 5-19, p. 108 Microtubules Many microtubules originate from centrosome Originate from centrioles Anchor major organelles Microtubules provide tracks for mobile organelles Microtubules Organelle movement by motor proteins Vesicle attached to motor protein “walks” along microtubule Requires ATP Cytoskeleton allows large cellular movement Amoeboid motion, cytoplasmic streaming, cell division Kinesin Fig. 5-20a,b, p. 108 Flagellar and Ciliary Beating Patterns Fig. 5-22, p. 110 Taxol, a drug approved for treatment of breast cancer, prevents depolymerization of microtubules. What cellular function that affects cancer cells more than normal cells might taxol interfere with 1. 2. 3. Maintaining cell shape Cilia or flagella Chromosome movements in cell division 33% 1 ? 33% 2 33% 3 Specialized Structures of Plant Cells Chloroplasts are biochemical factories powered by sunlight Central vacuoles have diverse roles in storage, structural support, and cell growth Cell walls support and protect plant cells Chloroplasts Chloroplasts have multiple membranes for photosynthesis Outer smooth, inner folded; stroma inside both Thylakoids and grana inside stroma Endosymbiosis Plastids are plant organelles that include chloroplasts, amlyoplasts and chromoplasts Chloroplast Structure Fig. 5-24, p. 111 Central Vacuoles Central vacuoles Large vesicles in plants 90% of many plant cell’s volume Turgor pressure from water Other functions Tonoplast Membrane surrounding central vacuole Cell Walls Cell Extracellular structures Provide structure and contain pressure Cellulose fibers for tensile strength, other organic molecules for compression resistance Two walls types of cells walls Primary Secondary Cell Wall Structure Fig. 5-25, p. 112 The Animal Cell Surface Cell adhesion molecules organize animal cells into tissues and organs Cell junctions reinforce cell adhesions and provide avenues of communication The extracellular matrix organizes the cell exterior Cell Adhesion and Junctions Cell adhesion molecules bind cells together nonpermanently Glycoproteins bind to specific molecules on other cells Cell junctions seal spaces between cells permanently Direct cellular communication Functions of Cellular Junction Anchoring junctions “weld” cells together Tight junctions prevent small ion movement Desmosomes and adherens Seal spaces and fuse membranes Gap junctions allow passage without membrane control Same tissue Animal Cell Connections Fig. 5-26, p. 114 Extracellular Matrix Collagen proteins Tensile strength and elasticity Proteoglycans Interlinkage Changes consistency (jellylike to hard and elastic) Fibronectins Connect cells via integrins Extracellular Matrix Fig. 5-27, p. 115 Video: Fluid mosaic model