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Transcript
Unit 2 The Cellular Basis of Life 2A. Basic Cell Structure and Function 2B. Viruses 2C. 2C Membranes and Cell Transport 2D. Energy and Metabolism 2E. How Cells Harvest Energy 2F. Photosynthesis 2G. Cell Communication Module 2A Basic Cell Structure and Function Cells are the basic units of life. Therefore, an understanding of cells is essential for an understandingg of livingg organisms. In this module, we will take an introductory look at the structure and function of living cells. 1 2 Objective # 1 Objective 1 In 1655, the English scientist Robert Hooke coined the term “cellulae” for the small box box--like structures he saw while examining a thin slice of cork under a microscope. A few years later, a Dutchman named Anton van Leeuwenhoek observed and described numerous living cells. Describe the general plan of cellular organization common to all cells. 3 4 Onion Cells Objective 1 Further 5 study has shown that all cells have the following basic structure : ¾ A thin, flexible plasma membrane surrounds the entire cell. ¾ The interior is filled with a semisemi-fluid material called the cytoplasm. cytoplasm. ¾ Also inside are specialized structures called organelles and the cell’s genetic material.. material 6 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Objective # 2 Plasma membrane Cytoplasm List and explain the 3 principles i i l off the h cellll theory. h O Organelles ll Genetic material Identify the Basic Components of a cell 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Objective 2 Objective 2 In 1838 – 1839, the German scientists Schleiden and Schwann Schwann,, proposed the first 2 principles of the cell theory: About 15 years later, the German physician Rudolf Virchow proposed the third and final principle of the cell theory: ¾ All cells arise from prepre-existing cells. ¾ All organisms are composed of one or more cells. ¾ Cells are the basic units of life. This is now qualified with “under the current conditions on earth”. 9 10 Objective # 3 Objective 3 Why are cells so small? ¾ Because a cell usually has only 1 or 2 sets of genetic instructions, there is a limit to the volume of cytoplasm that can be effectively controlled. controlled ¾ Methods used to transport materials and information inside the cell are efficient over short distances only. ¾ Problem with surfacesurface-toto-volume ratio. Describe some factors that act to limit cell size. size 11 12 2 Objective 3 Assuming constant shape, as an object gets bigger what happens to its surface area? What happens to its volume? What happens to its surfacesurface-toto-volume ratio? ¾ The S/V ratio decreases because volume increases at a faster rate than surface area. The ratio of Surface Area to Volume gets smaller as this cell gets larger 1 unit 10 unit Surface area (4πr2) 12.57 unit2 1257 unit2 Volume ( 43 πr3) 4.189 unit3 4189 unit3 3 0.3 Cell radius (r) Surface Area- /Volume 13 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Objective 3 Objective 3 Why is decreasing S/V ratio a problem? In order to survive , a cell must exchange materials with its environment. Cell volume determines the amount of materials that must be exchanged, while surface area limits how fast exchange can occur. In other words, as cells get larger the need for materials increases faster than the ability to absorb them. How have organisms become larger in spite of these problems? At first, single g cells simply p got g larger. g Average eukaryotic cell is 1,000 X larger in volume than average prokaryotic cell. Eventually, limits to size of individual cells were reached. 15 16 Objective 3 Objective 3 Colonial Coenocytic organisms – sac of cytoplasm continued to increase in size but became multinucleate and evolved thin, flat shapes or long, narrow shapes to increase S/V ratio. e.g. some protists, fungi 17 organisms – instead of one large mass of cytoplasm, body was divided into many small, similar cells, each with its own nucleus. e.g. some protists Multicellular organisms – similar to colonial except cells became specialized to carry out specific functions. e.g. plants, animals 18 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Objective # 4 Objective 4 Be able to describe the structure and function all cell parts shown on this diagram of a typical prokaryotic cell Describe the structure of a typical i l prokaryotic k i cell. ll 19 Cytoplasm Ribosomes Nucleoid (DNA) Pl Plasma membrane b Cell wall Capsule Pili Flagellum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display. Fig. 4.4 Electron micrograph of a photosynthetic prokaryotic cell Nucleoid Cytoplasm Cell wall Plasma membrane 0.6 µm 22 Photosynthetic membranes Courtesy of E.H. Newcomb & T.D. Pugh, University of Wisconsin Objective # 5 Nucleus Nuclear envelope Nucleolus Nuclear pore Ribosomes Rough endoplasmic reticulum Smooth endoplasmic reticulum Microvilli Cytoskeleton Actin filament Microtubule Ribosomes Intermediate filament Describe the structure of a typical i l eukaryotic k i cell. ll C ti l Centriole Cytoplasm Lysosome Be able to describe the structure and function of all cell parts shown on this diagram of a typical animal cell 23 Exocytosis Vesicle Golgi apparatus Plasma membrane Peroxisome Mitochondrion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosome Nucleus Nucleus Nuclear envelope Nuclear pore Nucleolus Intermediate filament Central vacuole Cytoskeleton Intermediate filament Microtubule Actin filament (microfilament) Peroxisome Mitochondrion Golgi apparatus Vesicle Chloroplast y p Cytoplasm Repository of the genetic information Most eukaryotic cells possess a single nucleus Nucleolus – region where ribosomal RNA synthesis takes place Nuclear envelope ¾ ¾ Be able to describe the structure and function of all cell parts shown on this diagram of a typical plant cell In eukaryotes, the DNA is divided into multiple linear chromosomes ¾ Adjacent cell wall Cell wall Plasma membrane 2 phospholipid bilayers b Nuclear pores – control passage in and out Chromatin is chromosomes plus protein Plasmodesmata 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ribosomes Cell’s Be able to describe the structure and function of the eukaryotic nucleus 27 protein synthesis machinery Found in all cell types in all 3 domains Ribosomal RNA (rRNA) (rRNA)--protein complex co pe Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA) Ribosomes may be free in cytoplasm or associated with internal membranes 28 Endomembrane System Fig. 4.9 A system of membranes that run through the cytoplasm and divide the cell into compartments where different cellular functions occur Present in e eukaryotic kar otic cells onl only Components of the endomembrane system include: the endoplasmic reticulum, the Golgi, lysosomes, lysosomes, microbodies, microbodies, vacuoles, and vesicles Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display. Large subunit Ribosome Small subunit Be able to describe the structure and function of ribosomes 30 5 Endoplasmic reticulum Be able to describe the structure and function of the rough and smooth endoplasmic reticulum: Rough endoplasmic reticulum (RER) ¾ Attachment of ribosomes to the membrane gives a rough appearance ¾ Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane S Smooth h endoplasmic d l i reticulum i l (SER) ¾ Relatively few bound ribosomes ¾ Variety of functions – synthesis, store Ca2+ , detoxification Ratio of RER to SER depends on cell’s function 32 31 Golgi apparatus Flattened stacks of interconnected membranes (Golgi bodies) Functions in packaging and distribution of molecules synthesized at one location and used at another within the cell or even outside of it Cis and trans faces Vesicles transport molecules to destination Be able to describe the structure and function of the Golgi apparatus: 34 33 Lysosomes Membrane Membrane--bound sacs that contain digestive enzymes Arise from the Golgi apparatus E Enzymes y es catalyze cata y e the t e breakdown b ea dow of o macromolecules Destroy cells or foreign matter that the cell has engulfed by phagocytosis 35 36 6 Vacuoles Microbodies Membrane Membrane--bounded sacs that carry out various functions depending on the cell type • Variety of enzyme‐ bearing, membrane‐ enclosed vesicles • One type are peroxisomes There – Contain enzymes involved in the oxidation of fatty acids – H2O2 produced as by‐ product – rendered harmless by catalase are different types of vacuoles: ¾ Central vacuole in plant cells vacuole of some protists ¾ Storage vacuoles ¾ Contractile 37 38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Nuclear pore Ribosome Be able to describe the movement of proteins through the endomembrane system of a eukaryotic cell: Electron micrograph showing the large central vacuole of a plant cell Rough endoplasmic reticulum Membrane protein Newly synthesized protein 1. Vesicle containing proteins buds from the rough endoplasmic reticulum, diffuses through the cell and ffuses cell, ses to the cis face of the Golgi apparatus. Transport vesicle Smooth endoplasmic reticulum cis face Golgi membrane protein Cisternae Golgi Apparatus trans face 2. The proteins are modified and packaged into vesicles for transport. Secretory vesicle Secreted protein Cell membrane 39 Mitochondria Found in all types of eukaryotic cells Bound by membranes ¾ ¾ ¾ ¾ 3. The vesicle may travel to the plasma membrane, releasing its contents to the extracellular environment. Extracellular fluid Be able to describe the structure and function of a mitochondrium: Outer membrane Intermembrane space Inner membrane has cristae Matrix On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism Have their own DNA 41 42 7 Chloroplasts Be able to describe the structure and function of a chloroplast: Organelles present in cells of plants and some other eukaryotes Contain chlorophyll for photosynthesis Surrounded by y 2 membranes Thylakoids are membranous sacs within the inner membrane ¾ Grana are stacks of thylakoids Have their own DNA 44 43 Endosymbiosis This theory proposes that some eukaryotic organelles evolved by a symbiosis between two cells that were each freefree-living One cell, a prokaryote, was engulfed by and became part of a larger cell cell, which hich was as the precursor of modern eukaryotes Organelles that probably arose by endosymbiosis include mitochondria and chloroplasts Some eukaryotic organelles evolved through the process of endosymbiosis: 46 45 Cytoskeleton A network of protein fibers and tubes found in all eukaryotic cells ¾ Supports the shape of the cell ¾ Keeps organelles in fixed locations system – constantly forming and disassembling 3 Components of the Cytoskeleton Microfilaments ((actin actin filaments) ¾ ¾ Microtubules ¾ ¾ Dynamic ¾ Largest of the cytoskeletal elements Dimers of αα- and ββ-tubulin subunits Facilitate movement of cell and materials within cell Intermediate filaments ¾ ¾ 47 Two protein chains loosely twined together Movements like contraction, crawling, “pinching” Between the size of actin filaments and microtubules Very stable – usually not broken down 48 8 Centrosome Be able to describe the structure and function of the 3 components of the cytoskeleton: Region containing a pair of centrioles Centrioles function as microtubulemicrotubuleorganizing centers. They can initiate the assembly of new microtubules. Animal cells and most protists have centrioles Plants and fungi usually lack centrioles 49 50 Cell Movement A pair of centrioles. Each centriole is composed of 9 triplets of microtubules: Essentially all cell motion is tied to the movement of actin filaments, microtubules, or both Some cells crawl using g actin microfilaments Eukaryotic flagella and cilia have 9 + 2 arrangement of microtubules Microtubule triplet ¾ Not like prokaryotic flagella Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display. Be able to describe the structure and function of a eukaryotic flagellum. Cilia have a similar structure, except they are shorter and more numerous. 52 A green algal cell with numerous flagella and a paramecium covered with cilia 53 9 Extracellular matrix (ECM) Eukaryotic cell walls Animal Plants, fungi, and many protists ¾ Different from prokaryote ¾ Prokaryotes y peptidoglycan ¾ Plants and protists – cellulose ¾ Fungi – chitin ¾ Plants – primary and secondary cell walls ¾ 55 Extracellular matrix surrounding an animal cell cells lack cell walls Secrete an elaborate mixture of glycoproteins into the space around them Collagen may be abundant Form a protective layer over the cell surface Integrins link ECM to cell’s cytoskeleton 56 Table 4.2 57 Objective # 6 Describe the similarities and differences between prokaryotic and eukaryotic cells. 59 60 10 Objective 6 Prokaryotes organisms monera (bacteria) Objective 6 Eukaryotes all other organisms Prokaryotes Eukaryotes always present always present size very small much larger (1 – 5 μm) (10 – 100 μm) complexity relatively simple more complex cell wall membranemembranebound organelles ribosomes cytoskeleton flagella usually present sometimes (contains present (lacks peptidoglycan) peptidoglycan) 61 Objective 6 Prokaryotes Eukaryotes absent present smaller and free in the cytoplasm absent solid flagellin; rotate larger and may be bound to ER present microtubules; bend plasma membrane internal may contain membranes b i f ldi infoldings off the plasma membrane but usually lack internal membranes complex system off internal i l membranes divides cell into specialized compartments 62 Objective 6 63 Prokaryotes Eukaryotes structure single, naked, many linear of genetic circular DNA chromosomes, material molecule each made of 1 DNA molecule joined with protein location in an area of inside a of genetic the cytoplasm membrane membrane--bound material called the nucleus nucleoid Objective # 7 64 Objective 7 Cell surface markers allow the cells of a multicellular organism to recognize each other and to distinguish “self” from “non“non-self.” In this section, we will examine 2 types of cell surface markers: Name and describe the types of surface markers that ggive cells identity. ¾ Glycolipids ¾ MHC 65 proteins 66 11 Objective 7 Objective 7 Glycolipids: MHC proteins: ¾ Are proteins embedded in the surface of the plasma membrane. ¾ Allow ow ce cellss of o the t e immune u e system syste to distinguish foreign cells from the body’s own cells so they can mount an attack against any foreign cells. ¾ Are lipids embedded in the plasma membrane with cabohydrate groups attached ¾ Allow cells that are part of the same tissue to recognize each other and form intimate connections to better coordinate their functions. 67 68 Objective # 8 Objective 8 Explain what cell junctions are, and discuss the following types of cell junctions: g junction j a) tight b) anchoring junction c) communicating junction Cell junctions refer to long long--lasting or permanent connections between adjacent cells. We will examine 3 types of cell junctions: 69 70 Objective 8a Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tight junction Adjacent plasma membranes a) Tight junctions connect cells into sheets. Because these junctions form a tight seal between cells, in order to cross the sheet,, substances must pass through the cells, they cannot pass between the cells. Tight junction proteins Intercellular space a. 2.5 µm Microvilli Tight Junction Tight junction Anchoring junction (desmosome) Intermediate filament Communicating junction Basal lamina 71 Courtesy of Daniel Goodenough 12 Objective 8b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anchoring Junction b) Anchoring junctions attach the cytoskeleton of a cell to the matrix surrounding the cell, or to the cytoskeleton of an adjacent cell. Microvilli Anchoring junction (desmosome) Intercellular space Adjacent plasma membranes Tight junction C dh in Cadherin Cytoplasmic protein plaque Anchoring junction (desmosome) Cytoskeletal filaments anchored to plaque b. Intermediate filament 0.1 µm Communicating junction Basal lamina 73 © Dr. Donald Fawcett/Visuals Unlimited. Objective 8c Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. c) Communicating junctions link the cytoplasms of 2 cells together, permitting the controlled p passage g of small molecules or ions between them. In animals, these junctions are called gap junctions junctions;; in plants they are called plasmodesmata plasmodesmata.. Communicating Junction Microvilli Tight junction Anchoring junction (desmosome) Intermediate filament Communicating junction Communicating junction Intercellular space Connexon Two adjacent connexons forming an open channel between cells Channel (diameter 1.5 nm) Adjacent plasma membranes 75 Plasmodesmata connect plant cells c. Basal lamina 1.4 µm © Dr. Donald Fawcett/Visuals Unlimited. Table 4.4 77 13