Chapter 6. A Tour of the Cell

Transcription

1 Chapter 6 A Tour of the Cell PowerPoint lectures are originally from Campbell / Reece Media Manager and Instructor Resources for BIOLOGY, 7 th & 8 th Edition by N. A. Campbell & J. B. Reece Copyright 2005 & 2008 Pearson Education, Inc. Publishing as Benjamin Cummings

2 In the Late 1600s. The English scientist Robert Hooke first observed plant cells with a crude microscope.

3 Robert Hooke Observed thin slices of cork Reminded him about the cells of the monks

4 In the 1830s Matthais Schleiden All living things are composed of cells. Theodor Schwann

5 In the 1800s The cells arise only from other cells. Rudolf Virchow All disease conditions of the organism can be attributed to diseased changes of the body cells.

6 Overview: The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live.

7 The Cell Theory The cell is an organism s basic unit of structure and function. All cells come from preexisting cells.

8 Cell Diversity The human body has: 50 to 100 trillion cells. Over 200 different types of cells Types of cells differ in size, shape, subcellular components, and functions

9 Electron microscope Light microscope Unaided eye LE 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

10 Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry Though usually too small to be seen by the unaided eye, cells can be complex

11 Microscopy Scientists use microscopes to visualize cells too small to see with the naked eye In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image

12 The Path of Light in the Light Microscope %20SCOPE%20DIAGRAM.JPG

13 Microscopy The quality of an image depends on: Magnification, the ratio of an object s image size to its real size Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points Contrast, visible differences in parts of the sample

14 Microscopy / Magnification Magnification, the ratio of an object s image size to its real size. LMs can magnify effectively to about 1,000 times the size of the actual specimen

15 Microscopy / Resolution Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points

16 Microscopy / Resolution The minimum resolution of a LM is about 200 nanometers (nm), the size of a small bacterium. The practical resolution limit of the electron microscope is closer to about 2 nm Most subcellular structures, or organelles, are too small to be resolved by a LM

17 Microscopy / Contrast - Contrast, visible differences in parts of the sample - Various techniques enhance contrast and enable cell components to be stained or labeled 50 µm Brightfield (unstained specimen) Brightfield (stained specimen) Fluorescence Phase-contrast

18 Electron Microscopes Electrons are used instead of light. Two basic types of electron microscopes (EMs) are used to study subcellular structures 1. Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEMs are used mainly to study the internal ultrastructure of cells

19 Transmission Electron Microscope (TEM)

20 Scanning Electron Microscope (SEM) 2. Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3D

21 LE 6-4 Scanning electron microscopy (SEM) Cilia 1 µm Transmission electron microscopy (TEM) Longitudinal section of cilium Cross section of cilium 1 µm

22 Isolating Organelles by Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Cell fractionation enables scientists to determine the functions of organelles

23 1000 g (1000 times the force of gravity) 10 min Supernatant poured into next tube 20,000 g 20 min Pellet rich in nuclei and cellular debris 80,000 g 60 min 150,000 g 3 hr Pellet rich in mitochondria (and chloroplasts if cells are from a plant) Pellet rich in microsomes (pieces of plasma membranes and cells internal membranes) Pellet rich in ribosomes

24 Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions Every organism has 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

25 Basic features of all cells All cells have the following features in common: Plasma membrane Cytoplasm Chromosomes (carry genes in the form of DNA) Ribosomes (make proteins according to instructions from the genes)

26 Comparing Prokaryotic and Eukaryotic Cells Prokaryotic cells are characterized by having No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles Cytoplasm bound by the plasma membrane

27 Prokaryotic Cells Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome (a) A typical rod-shaped bacterium Cell wall Capsule Flagella 0.5 µm (b) A thin section through the bacterium Bacillus coagulans (TEM)

28 Eukaryotic cells Eukaryotic cells are characterized by having DNA in a nucleus that is bounded by a membranous nuclear envelope Membrane-bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells

29 Cytoplasm s Components of Eukaryotic Cells The cytoplasm consists of: Organelles Cytosol Organelles: Specific entities, each carries out a specific function for the cell. Cytosol: The viscous, semitransparent fluid in which other cytoplasmic elements are suspended. Largely water with dissolved protein, salts, sugars, and other solutes.

30 Why Cells are Small? A smaller cell has a higher surface area to volume ratio, which facilitates the exchange of materials into and out of the cell. Larger organisms do NOT generally have larger cells than smaller organisms simply more cells

31 LE 6-7 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)

32 A Panoramic View of the Eukaryotic Cell Every cell is surrounded by a plasma membrane. The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of the cell Eukaryotic cells have internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles

33 LE 6-9a 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)

34 LE 6-9b 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

35 Concept 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 genes (DNA) in a eukaryotic cell. Functions of the nucleus: 1. The nucleus controls cellular activities by making proteins. 2. In the nucleus, DNA replication takes place to transmit information from parents to offspring.

36 The Nucleus: Genetic Library of the Cell The nucleus is made of the following parts: 1. The nuclear envelope: a double membrane with pores enclosing the nucleus,. 2. The nucleolus: Where components of ribosomes are synthesized and assembled to form ribosomal subunits. 3. The chromatin: the fibrous material in the nucleus of a nondividing cell, made of DNA and associated proteins.

37 LE 6-10 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)

38 Ribosomes: Protein Factories in the Cell Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations: In the cytosol. Free ribosomes synthesize proteins that function within the cytosol. On the outside of the endoplasmic reticulum (ER) or the nuclear envelope. Bound ribosomes synthesize proteins that: a. Build membranes b. Are to be exported from the cell.

39 LE 6-11 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

40 Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell In the cell, the endomembrane system is the membranous components that are either in direct contact or connected via transfer by vesicles. These components make up the endomembrane system that includes the: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane

41 The Endomembrane System Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi Plasma membrane

42 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 There are two distinct regions of ER: Smooth ER, which lacks ribosomes Rough ER, with ribosomes studding its surface

43 LE 6-12 Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Rough ER Transitional ER 200 nm

44 Functions of Smooth ER The smooth ER Synthesizes lipids Metabolizes carbohydrates Stores calcium ions necessary for muscle contraction. Detoxifies poisons and drugs

45 Functions of Rough ER The rough ER Has bound ribosomes Is a membrane factory for the cell Produces proteins that: a.build membranes b.are to be exported from the cell.

46 The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae

47 The Golgi Apparatus: Shipping and Receiving Center Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules, including some polysaccharides. Sorts and packages materials into transport vesicles

48 The Golgi Apparatus: Shipping and Receiving Center 1 Proteincontaining vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. 2 Proteins are modified within the Golgi compartments. 3 Proteins are then packaged within different vesicle types, depending on their ultimate destination. Rough ER Golgi apparatus Pathway A: Vesicle contents destined for exocytosis ER Phagosome membrane Proteins in cisterna Secretory vesicle Secretion by exocytosis Plasma membrane Pathway C: Lysosome containing acid hydrolase enzymes Vesicle becomes lysosome Pathway B: Vesicle membrane to be incorporated into plasma membrane Extracellular fluid Figure 3.20

49 Lysosomes: Digestive Compartments Lysosomes are membranous sacs of hydrolytic enzymes that digest macromolecules such as proteins, fats, polysaccharides, and nucleic acids. Functions of lysosomes: Intracellular digestion: Lysosomes can fuse with food vacuoles containing food items brought into the cell by phagocytosis. Recycle cell s own organic material: Lysosomes use enzymes to recycle organelles and macromolecules, a process called autophagy. Programmed cell destruction in multicellular organisms or apoptosis

50 LE 6-14a 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

51 LE 6-14b 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

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53 Vacuoles: Diverse Maintenance Compartments Vesicles and vacuoles (larger versions of vesicles) are membrane-bound sacs with varied functions A plant cell or fungal cell may have one or several vacuoles

54 Types of vacuoles in various cells: Food vacuoles are formed by phagocytosis Contractile vacuoles, found in many freshwater protists, pump excess water out of cells Central vacuoles, found in many mature plant cells. The membrane surrounding the central vacuole is called the tonoplast.

55 LE 6-15 Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm

56 Functions of the Central Vacuole: Stockpiling proteins and inorganic ions. Storing pigments. Storing defensive compounds against herbivores. Increasing the surface area to volume ratio for the whole cell.

57 The Endomembrane System: A Review The endomembrane system regulates protein traffic and performs metabolic functions in the cell

58 LE The Endomembrane System: A Review Nucleus Rough ER Smooth ER Nuclear envelope The endomembrane system: - regulates protein traffic within the cell - performs metabolic functions in the cell

59 LE The Endomembrane System: A Review Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi

60 LE The Endomembrane System: A Review Nucleus Rough ER Smooth ER Nuclear envelope cis Golgi Transport vesicle trans Golgi Plasma membrane

61 Concept 6.5: Mitochondria and chloroplasts change energy from one form to another Mitochondria and chloroplasts are not part of the endomembrane system. Both organelles have: 1- Small quantities of DNA 2- Their own ribosomes 3- Double membranes.

62 Mitochondria: Structure Mitochondria are in nearly all eukaryotic cells They have a smooth outer membrane and an inner membrane folded into cristae The inner membrane creates two compartments: intermembrane space and mitochondrial matrix

63 Mitochondria: Make ATP Mitochondria are the sites of cellular respiration, generating energy for the cell in the form of ATP. Cristae present a large surface area for enzymes that synthesize ATP

64 LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm

65 Chloroplasts: Capture of Light Energy Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis. In photosynthesis, the plants make sugar by using light energy, carbon dioxide and water. Chloroplasts are found in the leaves and other green organs of plants and in algae

66 LE 6-18 Chloroplast structure includes: -Thylakoid membranes: membranous sacs that are stacked in some regions like poker chips into grana (singular is granum) Chloroplast - Stroma, the internal fluid surrounding the thylakoid membanes. Chloroplast DNA Ribosomes Stroma Inner and outer membranes Granum Thylakoid 1 µm

67 Peroxisomes Peroxisomes are specialized metabolic compartments bounded by a single membrane Peroxisomes produce hydrogen peroxide and convert it to water. Peroxisomes in the liver detoxify alcohol and other harmful compounds. Peroxisome 1 µm

68 Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell The cytoskeleton is a network of fibers extending throughout the cytoplasm It helps to support the cell and maintain its shape It interacts with motor proteins to produce motility Inside the cell, vesicles can travel along monorails provided by the cytoskeleton It is composed of three types of molecular structures: Microtubules Microfilaments Intermediate filaments

69 Microtubules Microtubules are the thickest of the three components of the cytoskeleton

70 Microtubules / Maintenance of Cell Shape

71 Microtubules / Chromosome Movement in Cell Division

72 Microtubules / Organelle Movements ATP Vesicle Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton

73 Microtubules / Organelle Movements

74 Microtubules in Cellular Structures The following cellular structures have microtubules as a basic component: Centrioles Cilia and flagella

75 Centrosomes and Centrioles In many cells, microtubules grow out from a centrosome near the nucleus The centrosome is a microtubuleorganizing center In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring. Centrioles have (9 + 0) arrangement of microtubules.

76 Centrosomes

77 Microtubules / Centrioles Centrosome Microtubule Centrioles 0.25 µm Longitudinal section of one centriole Microtubules Cross section of the other centriole

78 Microtubules / Centrioles Centrosome matrix Centrioles (a) Microtubules Figure 3.25a

79 Microtubules / Cilia and Flagella

80 Microtubules / Cilia and Flagella Cilia and flagella are extensions of the plasma membrane that share a common ultrastructure: A core of microtubules sheathed by the plasma membrane. Cilia and flagella have (9 + 2) arrangement of microtubules. A basal body that anchors the cilium or flagellum with a (9 + 0) arrangement of microtubules.

81 Microtubules / Cilia and Flagella 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

82 Cilia and flagella differ in their beating patterns Power, or propulsive, stroke Recovery stroke, when cilium is returning to its initial position (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Figure 3.27

83 Components of the Cytoskeleton / Microfilament Microfilaments, also called actin filaments, are the thinnest components

84 Microfilaments (Actin Filaments) Microfilaments are solid rods built as a twisted double chain of actin subunits The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3D network just inside the plasma membrane to help support the cell s shape

85 Microfilaments in Microvilli Bundles of microfilaments make up the core of microvilli of intestinal cells Microvillus Actin filaments

86 Microfilaments / Changes in Cell Shape and Cell Motility (as in Pseudopodia)

87 Microfilaments / Muscle Contraction Actin filament Muscle cell Myosin filament Myosin arm Myosin motors in muscle cell contraction

88 Microfilaments / Animal Cell Division (Cleavage Furrow Formation)

89 Microfilaments / Cytoplasmic Streaming

90 Intermediate Filaments Intermediate filaments are fibers with diameters in a middle range between microtubules and microfilaments.

91 Intermediate Filaments / Anchorage of cell organelles

92 Intermediate Filaments / Formation of Nuclear Lamina Nuclear lamina (TEM)

93 Label The Cellular Organelles and Structures

94 Label The Cellular Organelles and Structures

95 Concept 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

96 Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells The cell wall: protects the plant cell maintains the plant cell shape prevents excessive uptake of water by the cell Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein

97 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

98 LE 6-28 Central vacuole of cell Plasma membrane Secondary cell wall Primary cell wall Central vacuole of cell Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata

99 Intercellular Junctions in Plants Plasmodesmata are channels between adjacent plant cells Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes

100 The Extracellular Matrix (ECM) of Animal Cells Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) The ECM is made up of glycoproteins and other macromolecules

101 Intercellular Junctions in Animals Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Intercellular junctions facilitate this contact. Animals have 3 main types of intercellular junctions: Tight junctions. Desmosomes (anchoring junctions). Gap (Communicating) junctions.

102 Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Interlocking junctional proteins Intercellular space (a) Tight junctions: Impermeable junctions prevent molecules from passing through the intercellular space. Figure 3.5a

103 Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Intercellular space Plaque Intermediate filament (keratin) Linker glycoproteins (cadherins) (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. Figure 3.5b

104 Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Intercellular space Channel between cells (connexon) (c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication. Figure 3.5c

105 LE 6-31 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

106 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

107 You should now be able to: 1. Distinguish between the following pairs of terms: magnification and resolution; prokaryotic and eukaryotic cell; free and bound ribosomes; smooth and rough ER 2. Describe the structure and function of the components of the endomembrane system 3. Briefly explain the role of mitochondria, chloroplasts, and peroxisomes 4. Describe the functions of the cytoskeleton 5. Describe four different intercellular junctions