Cell Structure and Function

Transcription

1 PowerPoint Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University C H A P T E R 3 Cell Structure and Function

2 Processes of Life Growth Reproduction Responsiveness Metabolism

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4 Figure 3.1 Examples of types of cells.

5 Prokaryotic and Eukaryotic Cells: An Overview Prokaryotes Composed of bacteria and archaea Lack nucleus Lack various internal structures bound with phospholipid membranes Are typically 1.0 µm in diameter or smaller Have a simple structure

6 Figure 3.2 Typical prokaryotic cell. Inclusions Ribosome Cytoplasm Nucleoid Glycocalyx Cell wall Flagellum Cytoplasmic membrane

7 Prokaryotic and Eukaryotic Cells: An Overview Eukaryotes Have nucleus Have internal membrane-bound organelles Are larger: µm in diameter Have more complex structure Composed of algae, protozoa, fungi, animals, and plants

8 Figure 3.3 Typical eukaryotic cell. Nuclear envelope Nuclear pore Nucleolus Cilium Lysosome Mitochondrion Centriole Secretory vesicle Golgi body Transport vesicles Ribosomes Rough endoplasmic reticulum Smooth endoplasmic reticulum Cytoskeleton Cytoplasmic membrane

9 Figure 3.4 Approximate size of various types of cells.

10 External Structures of Bacterial Cells Glycocalyces Gelatinous, sticky substance surrounding the outside of the cell Composed of polysaccharides, polypeptides, or both

11 External Structures of Bacterial Cells Two Types of Glycocalyces Capsule Composed of organized repeating units of organic chemicals Firmly attached to cell surface May prevent bacteria from being recognized by host Slime layer Loosely attached to cell surface Water soluble Sticky layer allows prokaryotes to attach to surfaces

12 Figure 3.5 Glycocalyces. Glycocalyx (capsule) Glycocalyx (slime layer)

13 Motility PLAY Motility

14 External Structures of Bacterial Cells Flagella Are responsible for movement Have long structures that extend beyond cell surface Are not present on all bacteria

15 External Structures of Bacterial Cells Flagella Structure Composed of filament, hook, and basal body Basal body anchors the filament and hook to cell wall

16 Flagella: Structure PLAY Flagella: Structure

17 Figure 3.6 Proximal structure of bacterial flagella. Filament Direction of rotation during run Rod Peptidoglycan layer (cell wall) Protein rings Cytoplasm Cytoplasmic membrane Filament Gram + Gram Basal body Outer protein rings Rod Integral protein Inner protein rings Integral protein Cytoplasm Outer membrane Peptidoglycan layer Cytoplasmic membrane Cell wall

18 Figure 3.7 Micrographs of basic arrangements of bacterial flagella.

19 Flagella: Arrangement PLAY Flagella: Arrangement

20 Spirochetes PLAY Spirochetes

21 Figure 3.8 Axial filament. Axial filament Endoflagella rotate Axial filament rotates around cell Outer membrane Cytoplasmic membrane Spirochete corkscrews and moves forward Axial filament

22 External Structures of Bacterial Cells Flagella Function Rotation propels bacterium through environment Rotation reversible; can be counterclockwise or clockwise Bacteria move in response to stimuli (taxis) Runs Tumbles

23 Figure 3.9 Motion of a peritrichous bacterium.

24 Flagella: Movement PLAY Flagella: Movement

25 External Structures of Bacterial Cells Fimbriae and Pili Fimbriae Sticky, bristlelike projections Used by bacteria to adhere to one another and to substances in environment Shorter than flagella Serve an important function in biofilms

26 Figure 3.10 Fimbriae. Flagellum Fimbria

27 External Structures of Prokaryotic Cells Pili Special type of fimbria Also known as conjugation pili Longer than fimbriae but shorter than flagella Bacteria typically only have one or two per cell Transfer DNA from one cell to another (conjugation)

28 Figure 3.11 Pili. Pilus

29 Bacterial Cell Walls Provide structure and shape and protect cell from osmotic forces Assist some cells in attaching to other cells or in resisting antimicrobial drugs Can target cell wall of bacteria with antibiotics Give bacterial cells characteristic shapes Composed of peptidoglycan Scientists describe two basic types of bacterial cell walls Gram-positive and Gram-negative

30 Figure 3.12 Bacterial shapes and arrangements.

31 Figure 3.13 Possible structure of peptidoglycan. Sugar backbone Tetrapeptide (amino acid) crossbridge Connecting chain of amino acids

32 Bacterial Cell Walls Gram-Positive Bacterial Cell Walls Relatively thick layer of peptidoglycan Contain unique polyalcohols called teichoic acids Appear purple following Gram staining procedure Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation

33 Figure 3.14a Comparison of cell walls of Gram-positive and Gram-negative bacteria. Peptidoglycan layer (cell wall) Cytoplasmic membrane Gram-positive cell wall Lipoteichoic acid Teichoic acid Integral protein

34 Prokaryotic Cell Walls Gram-Negative Bacterial Cell Walls Have only a thin layer of peptidoglycan Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS) Lipid A portion of LPS can cause fever, vasodilation, inflammation, shock, and blood clotting May impede the treatment of disease Appear pink following Gram staining procedure

35 Figure 3.14b Comparison of cell walls of Gram-positive and Gram-negative bacteria. Porin Outer membrane of cell wall Peptidoglycan layer of cell wall Porin (sectioned) Periplasmic space Gram-negative cell wall Cytoplasmic membrane Lipopolysaccharide (LPS) layer, containing lipid A Integral proteins Phospholipid layers

36 Prokaryotic Cell Walls Bacteria Without Cell Walls A few bacteria lack cell walls Often mistaken for viruses due to small size and lack of cell wall Have other features of prokaryotic cells such as ribosomes

37 Bacterial Cytoplasmic Membranes Structure Referred to as phospholipid bilayer Composed of lipids and associated proteins Integral proteins Peripheral proteins Fluid mosaic model describes current understanding of membrane structure

38 Figure 3.15 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer. Head, which contains phosphate (hydrophilic) Phospholipid Tail (hydrophobic) Integral proteins Cytoplasm Phospholipid bilayer Integral protein Peripheral protein Integral protein

39 Bacterial Cytoplasmic Membranes Function Energy storage Harvest light energy in photosynthetic bacteria Selectively permeable Naturally impermeable to most substances Proteins allow substances to cross membrane Maintain concentration and electrical gradient

40 Figure 3.16 Electrical potential of a cytoplasmic membrane. Cell exterior (extracellular fluid) 30 mv Na + Cl Cytoplasmic membrane Integral protein Protein DNA Protein Cell interior (cytoplasm)

41 Passive Transport: Principles of Diffusion PLAY Passive Transport: Principles of Diffusion

42 Bacterial Cytoplasmic Membranes Function Passive processes Diffusion Facilitated diffusion Osmosis

43 Figure 3.17 Passive processes of movement across a cytoplasmic membrane.

44 Figure 3.18 Osmosis, the diffusion of water across a semipermeable membrane.

45 Figure 3.19 Effects of isotonic, hypertonic, and hypotonic solutions on cells. Cells without a wall (e.g., mycoplasmas, animal cells) H 2 O H 2 O H 2 O Cell wall Cell wall Cells with a wall (e.g., plants, fungal and bacterial cells) H 2 O H 2 O H 2 O Cell membrane Isotonic solution Cell membrane Hypertonic solution Hypotonic solution

46 Passive Transport: Special Types of Diffusion PLAY Passive Transport: Special Types of Diffusion

47 Prokaryotic Cytoplasmic Membranes Function Active processes Active transport Group translocation Substance is chemically modified during transport

48 Figure 3.20 Mechanisms of active transport. Extracellular fluid Uniport Cytoplasmic membrane ADP ATP P ADP ATP P Symport Cytoplasm Uniport Antiport Coupled transport: uniport and symport

49 Active Transport: Overview PLAY Active Transport: Overview

50 Active Transport: Types PLAY Active Transport: Types

51 Figure 3.21 Group translocation. Glucose Extracellular fluid PO 4 Cytoplasm Glucose 6-PO 4

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53 Cytoplasm of Bacteria Cytosol Liquid portion of cytoplasm Mostly water Contains cell's DNA in region called the nucleoid Inclusions May include reserve deposits of chemicals

54 Figure 3.22 Granules of PHB in the bacterium Azotobacter chroococcum. Pilus

55 Cytoplasm of Bacteria Endospores Unique structures produced by some bacteria Defensive strategy against unfavorable conditions Vegetative cells transform into endospores when multiple nutrients are limited Resistant to extreme conditions such as heat, radiation, chemicals

56 Figure 3.23 The formation of an endospore. Steps in Endospore Formation Cell wall Cytoplasmic membrane 1 DNA is replicated. Vegetative cell DNA 5 A cortex of peptidoglycan is deposited between the membranes; meanwhile, dipicolinic acid and calcium ions accumulate within the center of the endospore. Cortex 2 DNA aligns along the cell s long axis. 6 Spore coat forms around endospore. Spore coat 3 Cytoplasmic membrane invaginates to form forespore. Forespore 7 Endospore matures: completion of spore coat and increase in resistance to heat and chemicals by unknown process. Outer spore coat Endospore 4 Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell s DNA disintegrates. First membrane Second 8 membrane Endospore is released from original cell.

57 Cytoplasm of Prokaryotes Nonmembranous Organelles Ribosomes Sites of protein synthesis Composed of polypeptides and ribosomal RNA Cytoskeleton Composed of three or four types of protein fibers Can play different roles in the cell Cell division Cell shape Segregate DNA molecules Move through the environment

58 Figure 3.24 A simple helical cytoskeleton.

59 External Structures of Archaea Glycocalyces Function in the formation of biofilms Adhere cells to one another and inanimate objects Flagella Consist of basal body, hook, and filament Numerous differences with bacterial flagella Fimbriae and hami Many archaea have fimbriae Some make fimbria-like structures called hami Function to attach archaea to surfaces

60 Figure 3.25 Archaeal hami. Hamus Grappling hook Prickles

61 Archaeal Cell Walls and Cytoplasmic Membranes Most archaea have cell walls Do not have peptidoglycan Contain variety of specialized polysaccharides and proteins All archaea have cytoplasmic membranes Maintain electrical and chemical gradients Control import and export of substances from the cell

62 Figure 3.26 Representative shapes of archaea.

63 Cytoplasm of Archaea Archaeal cytoplasm similar to bacterial cytoplasm 70S ribosomes Fibrous cytoskeleton Circular DNA Archaeal cytoplasm also differs from bacterial cytoplasm Different ribosomal proteins Different metabolic enzymes to make RNA Genetic code more similar to eukaryotes

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65 External Structure of Eukaryotic Cells Glycocalyces Not as organized as prokaryotic capsules Help anchor animal cells to each other Strengthen cell surface Provide protection against dehydration Function in cell-to-cell recognition and communication

66 Eukaryotic Cell Walls and Cytoplasmic Membranes Fungi, algae, plants, and some protozoa have cell walls Composed of various polysaccharides Cellulose found in plant cell walls Fungal cell walls composed of cellulose, chitin, and/or glucomannan Algal cell walls composed of a variety of polysaccharides

67 Figure 3.27 A eukaryotic cell wall. Cytoplasmic membrane Cell wall

68 Eukaryotic Cell Walls and Cytoplasmic Membranes All eukaryotic cells have cytoplasmic membrane Are a fluid mosaic of phospholipids and proteins Contain steroid lipids to help maintain fluidity Contain regions of lipids and proteins called membrane rafts Control movement into and out of cell

69 Figure 3.28 Eukaryotic cytoplasmic membrane. Cytoplasmic membrane Intercellular matrix Cytoplasmic membrane

70 Figure 3.29 Endocytosis. Pseudopodium

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72 Cytoplasm of Eukaryotes Flagella Structure and arrangement Differ structurally and functionally from prokaryotic flagella Within the cytoplasmic membrane Shaft composed of tubulin arranged to form microtubules Filaments anchored to cell by basal body; no hook May be single or multiple; generally found at one pole of cell Function Do not rotate but undulate rhythmically

73 Figure 3.30a-b Eukaryotic flagella and cilia. Flagellum Cilia

74 Cytoplasm of Eukaryotes Cilia Shorter and more numerous than flagella Coordinated beating propels cells through their environment Also used to move substances past the surface of the cell

75 Figure 3.30c Eukaryotic flagella and cilia. Cytoplasmic membrane Cytosol Central pair microtubules Microtubules (doublet) arrangement Cytoplasmic membrane Basal body Portion cut away to show transition area from doublets to triplets and the end of central microtubules Microtubules (triplet) arrangement

76 Figure 3.31 Movement of eukaryotic flagella and cilia.

77 Cytoplasm of Eukaryotes Other Nonmembranous Organelles Ribosomes Larger than prokaryotic ribosomes (80S versus 70S) Composed of 60S and 40S subunits Cytoskeleton Extensive network of fibers and tubules Anchors organelles Produces basic shape of the cell Made up of tubulin microtubules, actin microfilaments, and intermediate filaments

78 Figure 3.32 Eukaryotic cytoskeleton. Microtubule 25 nm Microfilament Actin subunit Intermediate filament 7 nm Tubulin Protein subunits 10 nm

79 Cytoplasm of Eukaryotes Other Nonmembranous Organelles Centrioles and centrosome Centrioles play a role in mitosis, cytokinesis, and formation of flagella and cilia Centrosome is region of cytoplasm where centrioles are found Not found in all eukaryotic cells

80 Figure 3.33 Centrosome. Centrosome (made up of two centrioles) Microtubules Triplet

81 Cytoplasm of Eukaryotes Membranous Organelles Nucleus Often largest organelle in cell Contains most of the cell's DNA Semiliquid portion called nucleoplasm Contains chromatin RNA synthesized in nucleoli present in nucleoplasm Surrounded by nuclear envelope Contains nuclear pores

82 Figure 3.34 Eukaryotic nucleus. Nucleolus Nucleoplasm Chromatin Nuclear envelope Two phospholipid bilayers Nuclear pores Rough ER

83 Cytoplasm of Eukaryotes Membranous Organelles Endoplasmic reticulum Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope Functions as transport system Two forms Smooth endoplasmic reticulum (SER) Rough endoplasmic reticulum (RER)

84 Figure 3.35 Endoplasmic reticulum. Membrane-bound ribosomes Mitochondrion Free ribosome Smooth endoplasmic reticulum (SER) Rough endoplasmic reticulum (RER)

85 Cytoplasm of Eukaryotes Membranous Organelles Golgi body Receives, processes, and packages large molecules for export from cell Packages molecules in secretory vesicles that fuse with cytoplasmic membrane Composed of flattened hollow sacs surrounded by phospholipid bilayer Not in all eukaryotic cells

86 Figure 3.36 Golgi body. Secretory vesicles Vesicles arriving from ER

87 Cytoplasm of Eukaryotes Membranous Organelles Lysosomes, peroxisomes, vacuoles, and vesicles Store and transfer chemicals within cells May store nutrients in cell Lysosomes contain catabolic enzymes Peroxisomes contain enzymes that degrade poisonous wastes

88 Figure 3.37 Vacuole. Cell wall Nucleus Central vacuole Cytoplasm

89 Figure 3.38 The roles of vesicles in endocytosis and exocytosis. Bacterium Endocytosis (phagocytosis) Phagosome (food vesicle) Vesicle fuses with a lysosome Smooth endoplasmic reticulum (SER) Transport vesicle Lysosome Phagolysosome Golgi body Secretory vesicle Exocytosis (elimination, secretion)

90 Cytoplasm of Eukaryotes Membranous Organelles Mitochondria Have two membranes composed of phospholipid bilayer Produce most of cell's ATP Interior matrix contains 70S ribosomes and circular molecule of DNA

91 Figure 3.39 Mitochondrion. Outer membrane Inner membrane Crista Matrix Ribosomes

92 Cytoplasm of Eukaryotes Membranous Organelles Chloroplasts Light-harvesting structures found in photosynthetic eukaryotes Use light energy to produce ATP Have two phospholipid bilayer membranes and DNA Have 70S ribosomes

93 Figure 3.40 Chloroplast. Granum Stroma Thylakoid space Thylakoid Inner bilayer membrane Outer bilayer membrane

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95 Cytoplasm of Eukaryotes Endosymbiotic Theory Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes Smaller prokaryotes became internal parasites Parasites lost ability to exist independently Larger cell became dependent on parasites for aerobic ATP production Aerobic prokaryotes evolved into mitochondria Similar scenario for origin of chloroplasts Theory is not universally accepted

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