NOTES: CH 6 A Tour of the Cell

Transcription

1 NOTES: CH 6 A Tour of the Cell

2 Overview: The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells

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5 Electron microscope Light microscope Unaided eye 10 m 1 m 0.1 m Human height Length of some nerve and muscle cells Chicken egg 1 cm 1 mm Frog egg Measurements 1 centimeter (cm) = 10 2 meter (m) = 0.4 inch 1 millimeter (mm) = 10 3 m 1 micrometer (µm) = 10 3 mm = 10 6 m 1 nanometer (nm) = 10 3 µm = 10 9 m 100 µm 10 µm Most plant and animal cells Nucleus Most bacteria 1 µm Mitochondrion 100 nm Smallest bacteria Viruses 10 nm Ribosomes Proteins 1 nm Lipids Small molecules 0.1 nm Atoms

6 6.1 Biologists use microscopes and the tools of biochemistry to study cells

7 Brightfield (unstained specimen) Brightfield (stained specimen) 50 µm Phase-contrast

8 MICROSCOPES 1) Light Microscope 2) Electron Microscope (1950 s) Transmission Electron Microscope Scanning Electron Microscope

9 Light Microscope works by passing visible light through a thin section of specimen and then through glass lenses resolving power = 0.2 µm (size of small bacteria) max. magnification about 1000x

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11 Electron Microscope (1950 s) uses electron beams which have shorter wavelengths of light resolving power = 0.2 nm (most cell structures) magnification up to 40,000x

12 Electron Microscope 1) Transmission Electron Microscope -electrons transmitted through specimen are focused and image is magnified using electromagnets -used to study internal cell structure 2) Scanning Electron Microscope -electron beam scans the surface of a spec. -useful for studying the surface of specimen in 3-D.

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14 Disadvantages to EM can only view dead cells (elaborate preparation) very expensive! zooxanthellae cells cultured from coral Aiptasia pulchella in a Scanning Electron Microscope

15 WE CAN ALSO STUDY CELLS BY... Cell Fractionation = disrupting cells to separate out cell organelles Centrifugation = spinning mixtures of cells and their parts at very high speeds; separates the components

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17 6.2 Eukaryotic cells have internal membranes that compartmentalize their functions

18 Types of CELLS: The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells (& are in the domain Eukarya)

19 ALL CELLS: have a cell membrane have cytoplasm / cytosol have ribosomes (make proteins) can reproduce & contain genetic material (DNA / chromatin / chromosomes)

20 CELLS CAN BE CLASSIFIED AS: 1) PROKARYOTES 2) EUKARYOTES

21 1) PROKARYOTES 2) EUKARYOTES oldest cells (3.5 billion years) single celled lack nucleus & membranebound organelles genetic material in a single, circular molecule (PLASMID) in region called NUCLEOID small (1-2 µm) Domains Bacteria and Archaea newer cells (1.5 billion years) single or multicellular have a true nucleus & membrane-bound organelles genetic material organized into CHROMOSOMES in NUCLEUS larger ( µm) Domain Eukarya, includes Kingdoms Protista, Fungi, Plantae, Animalia

22 Pili Nucleoid Ribosomes Bacterial chromosome Plasma membrane Cell wall Capsule Flagella 0.5 µm A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM)

23 although eukaryotic cells are larger than prokaryotes, there is a limit on cell size due to the logistics of carrying out cellular metabolism

24 Surface area increases while Total volume remains constant Total surface area (height x width x number of sides x number of boxes) Total volume (height x width x length X number of boxes) Surface-to-volume ratio (surface area volume)

25 PLASMA MEMBRANE: the boundary of every cell The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of the cell The general structure of a biological membrane is a double layer of phospholipids

26 Outside of cell Carbohydrate side chain Hydrophilic region Inside of cell 0.1 µm Hydrophobic region TEM of a plasma membrane Hydrophilic region Phospholipid Proteins Structure of the plasma membrane

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28 A Panoramic View of the Eukaryotic Cell: A eukaryotic cell has internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles

29 Flagellum ENDOPLASMIC RETICULUM (ER Rough ER Smooth ER Nuclear envelope Nucleolus NUCLEUS Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

30 NUCLEUS Centrosome Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes (small brown dots) Golgi apparatus Central vacuole Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Wall of adjacent cell Plasmodesmata In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

31 6.3 - The eukaryotic cell s genetic instructions are housed in the NUCLEUS and carried out by the ribosomes the nucleus contains most of the DNA in a eukaryotic cell ribosomes use the information from the DNA to make proteins

32 The Nucleus: Genetic Library of the Cell the nucleus contains most of the cell s genes and is usually the most conspicuous organelle the nuclear envelope encloses the nucleus, separating it from the cytoplasm houses the information / instructions for cell functioning and maintenance the control center of the cell averages 5 µm in diameter

33 Nucleus 1 µm Chromatin Nuclear envelope: Inner membrane Outer membrane Nucleolus Nucleus Nuclear pore Pore complex Surface of nuclear envelope 0.25 µm Ribosome Rough ER 1 µm Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM)

34 NUCLEAR ENVELOPE double membrane which encloses the nucleus -each of the 2 membranes is a phospholipid bilayer w/specific proteins -is perforated by pores which regulate molecular traffic into and out of the nucleus -RNA and proteins enter or leave the nucleus through these pores -breaks down prior to cell division

35 CHROMATIN fibrous, threadlike complex of DNA and histone proteins which make up chromosomes in eukaryotic cells

36 CHROMOSOMES compacted, coiled up chromatin; visible under microscope; form just prior to cell division; human cells have 46 chromosomes (23 pairs)

37 NUCLEOLUS dense, spherical region in the nucleus -visible in a nondividing cell -may be 2 or more per cell -packages ribosomal subunits from: 1) rrna: transcribed in nucleolus 2) RNA produced elsewhere in nucleus -ribosomal subunits pass through nuclear pores to the cytoplasm where assembly into ribosomes is completed

38 RIBOSOMES cytoplasmic organelle; site of protein synthesis -made of RNA and protein -made in the nucleolus -cells with high rates of protein synthesis have large numbers of nucleoli & ribosomes (e.g. human liver cells have millions)

39 RIBOSOMES Ribosomes carry out protein synthesis in two locations: -in the cytosol (free ribosomes) -attached to the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes)

40 Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome Small subunit

41 The Endomembrane System **all structures are essentially compartments, closed off by their membranes from the cytoplasm

42 6.4 - The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected via transfer vesicles

43 The Endoplasmic Reticulum: Biosynthetic Factory The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope

44 ENDOPLASMIC RETICULUM (ER): extensive network of tubules and sacs used for transport and/or modification of proteins; can be ROUGH (ribosomes) or SMOOTH (no ribosomes)

45 Rough ER: manufactures secretory proteins and membranes ; proteins made here may be modified (i.e. folded into their tertiary structure) usually closer in to nucleus than smooth ER

46 Smooth ER: synthesizes lipids, phospholipids, steroids participates in carbohydrate metabolism detoxifies drugs and poisons stores calcium ions (for muscle contraction)

47 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Rough ER Transitional ER 200 nm

48 The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles

49 GOLGI APPARATUS: cis face (forming face; faces the rough ER) receives products by accepting transport vesicles from the rough ER trans face (maturing face; faces the cell membrane) pinches off vesicles from the Golgi and transports molecules to other sites

50 Golgi apparatus cis face ( receiving side of Golgi apparatus) Vesicles also transport certain proteins back to ER Vesicles move from ER to Golgi Vesicles coalesce to form new cis Golgi cisternae Cisternae 0.1 µm Cisternal maturation: Golgi cisternae move in a cisto-trans direction Vesicles transport specific proteins backward to newer Golgi cisternae Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma membrane for secretion trans face ( shipping side of Golgi apparatus) TEM of Golgi apparatus

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52 Lysosomes: Digestive Compartments A lysosome is a membranous sac of hydrolytic enzymes Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy

53 Nucleus 1 µm Lysosome Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Plasma membrane Lysosome Digestive enzymes Digestion Food vacuole Phagocytosis: lysosome digesting food

54 Lysosome containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Autophagy: lysosome breaking down damaged organelle

55 LYSOSOMES probably pinch off from the trans face of Golgi; are responsible for intracellular digestion; recycle the cell s own organic material; destroy cells

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57 Other Membrane-Bound Organelles: 1) Vacuoles 2) Peroxisomes

58 VESICLES / VACUOLES: membrane-enclosed sac used for storage and/or transport animal cells, vacuoles are small and look like vesicles **Vacuoles in plants have special characteristics: -plant cells have a LARGE central vacuole that stores water and watersoluble organic compounds and inorganic ions (K + and Cl - );

59 PLANT VACUOLES contain soluble pigments in some cells (red and blue pigments in flowers); play a role in plant growth by absorbing water and elongating the cell;

60 PLANT VACUOLES help protect from predators by storing waste products that may also be poisonous compounds Are surrounded by a membrane called the TONOPLAST some fresh-water protists have a contractile vacuole that pumps excess water from the cell

61 Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm

62 The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell s compartmental organization

63 Nucleus Rough ER Smooth ER Nuclear envelope

64 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi

65 Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi Plasma membrane

66 6.5 - Mitochondria and chloroplasts change energy from one form to another Mitochondria are the sites of cellular respiration Chloroplasts, found only in plants and algae, are the sites of photosynthesis Mitochondria and chloroplasts are not part of the endomembrane system Peroxisomes are oxidative organelles

67 MITOCHONDRIA: sites of cellular respiration found in nearly all eukaryotic cells the # in cells varies and is related to the cell s metabolic activity

68 inner membrane is convoluted and contains proteins/enzymes involved in cellular respiration inner membranes many infoldings are called CRISTAE; they increase the surface area for cellular respiration reactions to occur region within inner membrane is the MITOCHONDRIAL MATRIX Mitochondria in a human liver cell

69 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm

70 CHLOROPLASTS: ( the organelles that feed the world ) contain chlorophyll; site of photosynthesis (convert light energy into chemical energy; found in eukaryotic algae, leaves and other green plant organs; can change shape, move and divide

71 Chloroplasts: Capture of Light Energy Chloroplast structure includes: -Thylakoids, membranous sacs -Stroma, the internal fluid

72 Chloroplast Chloroplast DNA Ribosomes Stroma Inner and outer membranes Granum Thylakoid 1 µm

73 PEROXISOMES: contain special enzymes for specific metabolic pathways found in nearly all eukaryotic cells

74 contain peroxide-producing enzymes that transfer hydrogen ions to oxygen producing hydrogen peroxide contain catalase enzyme which converts / detoxifies hydrogen peroxide to water

75 Chloroplast Peroxisome Mitochondrion 1 µm

76 6.6 - The cytoskeleton is a network of fibers that organizes structures and activities in the cell anchors and/or provides tracks for many organelles It is composed of three types of molecular structures: Microtubules Microfilaments Intermediate filaments

77 Microtubule 0.25 µm Microfilaments

78 Components of the Cytoskeleton Microtubules are the thickest of the three components of the cytoskeleton Microfilaments, also called actin filaments, are the thinnest components Intermediate filaments are fibers with diameters in a middle range

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80 Roles of the Cytoskeleton: Support, Motility, and Regulation the cytoskeleton helps to support the cell and maintain its shape it interacts with motor proteins to produce motility (movement) inside the cell, vesicles can travel along monorails provided by the cytoskeleton recent evidence suggests that the cytoskeleton may help regulate biochemical activities

81 ATP Vesicle Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton

82 Microtubule Vesicles 0.25 µm

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84 Microtubules: straight, hollow rods made of protein called TUBULIN; can serve as tracks to guide organelle movement; involved in separation of chromosomes in cell division; make up CENTRIOLES;

85 Cilia and Flagella Microtubules control the beating of cilia and flagella, locomotor appendages of some cells Cilia and flagella differ in their beating patterns

86 FLAGELLA and CILIA: FLAGELLA: longer than cilia; usually found singly or in pairs; used to propel a cell CILIA: shorter than flagella; usually present in great numbers; wavelike motion used to sweep extracellular material over/away from cell

87 Direction of swimming Motion of flagella 5 µm

88 Direction of organism s movement Direction of active stroke Direction of recovery stroke Motion of cilia 15 µm

89 Cilia and flagella share a common ultrastructure: -A core of microtubules sheathed by the plasma membrane -A basal body that anchors the cilium or flagellum -A motor protein called DYNEIN, which drives the bending movements of a cilium or flagellum

90 Microtubules Plasma membrane Basal body 0.1 µm Outer microtubule doublet Dynein arms Central microtubule Cross-linking proteins inside outer doublets Radial spoke Plasma membrane 0.5 µm 0.1 µm Triplet Cross section of basal body

91 Microtubule doublets ATP Dynein walking Dynein arm

92 Cross-linking proteins inside outer doublets ATP Anchorage in cell Effect of cross-linking proteins Wavelike motion

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94 Microfilaments: can exist as single filaments or in bundles; formed from the protein ACTIN; help the cell (or parts of the cell) to contract; they stabilize cell shape; Involved in pinching contractions during cell division; Involved in forming pseudopodia that enable some cells to move. Yellow: nucleus Green: microfilaments throughout cytoplasm

95 Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium Amoeboid movement

96 Actin filament Muscle cell Myosin filament Myosin arm Myosin motors in muscle cell contraction

97 Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Vacuole Parallel actin filaments Cell wall Cytoplasmic streaming in plant cells

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99 Intermediate Filaments Intermediate filaments range in diameter from 8 12 nanometers, larger than microfilaments but smaller than microtubules They support cell shape and fix organelles in place Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes

100 6.7 - Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include: Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions

101 Extracellular Structures: CELL WALL: -semirigid structure outside of cell membrane of PLANT CELLS; -consists of CELLULOSE fibers + complex polysaccharides & proteins -provides support, limits cell s volume, and protects against fungi and/or microorganism infection.

102 Cell Walls of Plants Plant cell walls may have multiple layers: Primary cell wall: relatively thin and flexible Middle lamella: thin layer between primary walls of adjacent cells Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells

103 Central vacuole of cell Plasma membrane Secondary cell wall Primary cell wall Central vacuole of cell Middle lamella Central vacuole Cytosol 1 µm Plasma membrane Plant cell walls Plasmodesmata

104 The Extracellular Matrix (ECM) of Animal Cells: Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) Functions of the ECM: Support Adhesion Movement Regulation

105 Extracellular Structures: EXTRACELLULAR MATRIX: fibrous proteins such as COLLAGEN and glycoproteins are secreted by and surround cells; it holds cells together in tissues; helps filter materials passing between different tissues; orients cell movement during development; involved in cell-cell signalling.

106 Collagen fiber EXTRACELLULAR FLUID Proteoglycan complex Fibronectin Plasma membrane Integrin CYTOPLASM Microfilaments

107 Proteoglycan complex Polysaccharide molecule Carbohydrates Core protein Proteoglycan molecule

108 Intercellular Junctions Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact

109 Plants: Plasmodesmata Plasmodesmata are channels that perforate plant cell walls Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell

110 Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes

111 Animals: Tight Junctions, Desmosomes, and Gap Junctions At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells

112 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm Tight junction Intermediate filaments Desmosome Space between cells Gap junctions 1 µm Plasma membranes of adjacent cells Gap junction Extracellular matrix 0.1 µm

113 The Cell: A Living Unit Greater Than the Sum of Its Parts Cells rely on the integration of structures and organelles in order to function For example, a macrophage s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane

114 5 µm