Cell Structure. Chapter 4

Transcription

1 Cell Structure Chapter 4 1

2 Cells Cells were discovered in 1665 by Robert Hooke Early studies of cells were conducted by Mathias Schleiden (1838) Theodor Schwann (1839) Schleiden and Schwann proposed the Cell Theory 2

3 Cell Theory 1. All organisms are composed of cells 2. Cells are the smallest living things 3. Cells arise only from pre-existing cells All cells today represent a continuous line of descent from the first living cells 3

4 Cell size is limited Most cells are relatively small due reliance on diffusion of substances in and out of cells Rate of diffusion affected by Surface area available Temperature Concentration gradient Distance 4

5 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell radius (r) 1 unit 10 unit Surace area (4πr 2 ) unit unit 2 Volume ( 4 3 πr 3 ) unit unit 3 Surface Area / Volume 3 0.3

6 Surface area-to-volume ratio Organism made of many small cells has an advantage over an organism composed of fewer, larger cells As a cell s size increases, its volume increases much more rapidly than its surface area Some cells overcome limitation by being long and skinny like neurons 6

7 Microscopes Not many cells are visible to the naked eye Most are less than 50 μm in diameter Resolution minimum distance two points can be apart and still be distinguished as two separate points Objects must be 100 μm apart for naked eye to resolve them as two objects rather than one 7

8 2 types Light microscopes Use magnifying lenses with visible light Resolve structures that are 200 nm apart Limit to resolution using light Electron microscopes Use beam of electrons Resolve structures that are 0.2 nm apart 8

9 Electron Microscope Light Microscope Human Eye Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 100 m Electron microscopes 10 m 1 m 10 cm 1 cm Adult human Chicken egg Transmission electron microscopes transmit electrons through the material 1 mm 100 m 10 m 1 m Frog egg Paramecium Human egg Human red blood cell Prokaryote Chloroplast Mitochondrion Scanning electron microscopes beam electrons onto the specimen surface 100 nm Large virus (HIV) Ribosome 10 nm Protein 1 nm Amino acid 0.1 nm (1 Å) Hydrogen atom 9 Logarithmic scale

10 Basic structural similarities 1. Nucleoid or nucleus where DNA is located 2. Cytoplasm Semifluid matrix of organelles and cytosol 3. Ribosomes Synthesize proteins 4. Plasma membrane Phospholipid bilayer 10

11 Prokaryotic Cells Simplest organisms Lack a membrane-bound nucleus DNA is present in the nucleoid Cell wall outside of plasma membrane Do contain ribosomes (not membranebound organelles) Two domains of prokaryotes Archaea Bacteria 11

12 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pilus Cytoplasm Ribosomes Nucleoid (DNA) Plasma membrane Cell wall Capsule Pili Flagellum 0.3 µm Phototake

13 Bacterial cell walls Most bacterial cells are encased by a strong cell wall composed of peptidoglycan Cell walls of plants, fungi, and most protists different Protect the cell, maintain its shape, and prevent excessive uptake or loss of water Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls Archaea lack peptidoglycan 13

14 Flagella Present in some prokaryotic cells May be one or more or none Used for locomotion Rotary motion propels the cell 14

15 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0.5 µm Hook Filament Outer membrane Peptidoglycan portion of cell wall Outer protein ring Inner protein ring H + H + Plasma membrane a. b. c. a: Eye of Science/Photo Researchers, Inc. 15

16 Eukaryotic Cells Possess a membrane-bound nucleus More complex than prokaryotic cells Hallmark is compartmentalization Achieved through use of membrane-bound organelles and endomembrane system Possess a cytoskeleton for support and to maintain cellular structure 16

17 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Nuclear envelope Ribosomes Rough endoplasmic reticulum Nucleolus Nuclear pore Intermediate filament Smooth endoplasmic reticulum Microvilli Cytoskeleton Actin filament (microfilament) Microtubule Intermediate filament Ribosomes Centriole Cytoplasm Lysosome Exocytosis Vesicle Golgi apparatus Plasma membrane Peroxisome Mitochondrion 17

18 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosome Nucleus Nuclear envelope Nuclear pore Nucleolus Intermediate filament Central vacuole Cytoskeleton Intermediate filament Microtubule Actin filament (microfilament) Peroxisome Mitochondrion Golgi apparatus Vesicle Cytoplasm Chloroplast Adjacent cell wall Cell wall Plasma membrane Plasmodesmata 18

19 Nucleus Repository of the genetic information Most eukaryotic cells possess a single nucleus Nucleolus region where ribosomal RNA synthesis takes place Nuclear envelope 2 phospholipid bilayers Nuclear pores control passage in and out In eukaryotes, the DNA is divided into multiple linear chromosomes Chromatin is chromosomes plus protein 19

20 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nuclear pores Nuclear envelope Nucleolus Chromatin Nucleoplasm Nuclear lamina Inner membrane Nuclear basket Outer membrane Cytoplasmic filaments a. Nuclear pore 20

21 Ribosomes Cell s protein synthesis machinery Found in all cell types in all 3 domains Ribosomal RNA (rrna)-protein complex Protein synthesis also requires messenger RNA (mrna) and transfer RNA (trna) Ribosomes may be free in cytoplasm or associated with internal membranes 21

22 Endomembrane System Series of membranes throughout the cytoplasm Divides cell into compartments where different cellular functions occur One of the fundamental distinctions between eukaryotes and prokaryotes 22

23 Endoplasmic reticulum Rough endoplasmic reticulum (RER) Attachment of ribosomes to the membrane gives a rough appearance Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane Smooth endoplasmic reticulum (SER) Relatively few bound ribosomes Variety of functions synthesis, store Ca 2+, detoxification Ratio of RER to SER depends on cell s function 23

24 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum Rough endoplasmic reticulum Smooth endoplasmic reticulum (inset): Dr. Donald Fawcett & R. Bolender/Visuals Unlimited 0.08 µm 24

25 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 Has cis and trans faces Vesicles transport molecules to destination 25

26 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transport vesicle cis face Fusing vesicle Forming vesicle trans face Secretory vesicle (inset): Dennis Kunkel/Phototake 1 µm 26

27 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Nuclear pore Ribosome Rough endoplasmic reticulum Membrane protein Newly synthesized protein 1. Vesicle containing proteins buds from the rough endoplasmic reticulum, diffuses through the cell, and fuses to the cis face of the Golgi apparatus. Transport vesicle cis face Smooth endoplasmic reticulum Golgi membrane protein Cisternae Golgi Apparatus 2. The proteins are modified and packaged into vesicles for transport. Cell membrane Extracellular fluid Secreted protein trans face Secretory vesicle 3. The vesicle may travel to the plasma membrane, releasing its contents to the extracellular environment. 27

28 Lysosomes Membrane-bounded digestive vesicles Arise from Golgi apparatus Enzymes catalyze breakdown of macromolecules Destroy cells or foreign matter that the cell has engulfed by phagocytosis 28

29 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ribosome Nucleus Nuclear pore Rough endoplasmic reticulum Membrane protein Hydrolytic enzyme Transport vesicle Cisternae cis face Golgi membrane protein Smooth endoplasmic reticulum trans face Golgi Apparatus Old or damaged organelle Lysosome Digestion Lysosome Food vesicle Breakdown of organelle Lysosome aiding in the breakdown of an old organelle Phagocytosis Lysosome aiding in the digestion of phagocytized particles 29

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31 Microbodies Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Variety of enzymebearing, membraneenclosed vesicles Peroxisomes Contain enzymes involved in the oxidation of fatty acids Hydrogen peroxide produced as byproduct rendered harmless by catalase 0.2 µm (inset): From S.E. Frederick and E.H. Newcomb, Microbody-like organelles in leaf cells, Science, 163: March Reprinted with permission from AAAS 31

32 Vacuoles Membrane-bounded structures in plants Various functions depending on the cell type There are different types of vacuoles: Central vacuole in plant cells Contractile vacuole of some fungi and protists Storage vacuoles 32

33 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Central vacuole Tonoplast Chloroplast Cell wall (inset): Henry Aldrich/Visuals Unlimited 1.5 µm 33

34 Mitochondria Found in all types of eukaryotic cells Bound by membranes 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 34

35 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Crista DNA Matrix Ribosome Intermembrane space Inner membrane Outer membrane (inset): Dr. Donald Fawcett & Dr. Porter/Visuals Unlimited 0.2 µm 35

36 Chloroplasts Organelles present in cells of plants and some other eukaryotes Contain chlorophyll for photosynthesis Surrounded by 2 membranes Thylakoids are membranous sacs within the inner membrane Grana are stacks of thylakoids Have their own DNA 36

37 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ribosome DNA Thylakoid membrane Outer membrane Inner membrane Thylakoid disk Granum Stroma Stroma Granum (inset): Dr. Jeremy Burgess/Photo Researchers, Inc. 1.5 µm 37

38 Endosymbiosis Proposes that some of today s eukaryotic organelles evolved by a symbiosis arising between two cells that were each freeliving One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes Mitochondria and chloroplasts 38

39 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Unknown Archaeon Nucleus Protobacterium Mitochondrion Chloroplast Cyanobacterium Modern Eukaryote Unknown Bacterium Nucleus Unknown Archaeon Mitochondrion Protobacterium Chloroplast Cyanobacterium Modern Eukaryote 39

40 Cytoskeleton Network of protein fibers found in all eukaryotic cells Supports the shape of the cell Keeps organelles in fixed locations Dynamic system constantly forming and disassembling 40

41 3 types of fibers Microfilaments (actin filaments) Two protein chains loosely twined together Movements like contraction, crawling, pinching Microtubules Largest of the cytoskeletal elements Dimers of α- and β-tubulin subunits Facilitate movement of cell and materials within cell Intermediate filaments Between the size of actin filaments and microtubules Very stable usually not broken down 41

42 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microtubule Intermediate filament Actin filament Cell membrane a. Actin filaments b. Microtubules c. Intermediate filament 42

43 Centrosomes Region surrounding centrioles in almost all animal cells Microtubule-organizing center Can nucleate the assembly of microtubules Animal cells and most protists have centrioles pair of organelles Plants and fungi usually lack centrioles 43

44 Centrioles Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microtubule triplet 44

45 Cell Movement Essentially all cell motion is tied to the movement of actin filaments, microtubules, or both Some cells crawl using actin microfilaments Flagella and cilia have arrangement of microtubules Not like prokaryotic flagella Cilia are shorter and more numerous 45

46 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Doublet microtubule Flagellum Radial spoke Dynein arm Plasma membrane Basal body Central microtubule pair 0.1 µm 0.1 µm (top & bottom insets): William Dentler, University of Kansas Microtubule triplet 46

47 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eukaryotic cell walls Plants, fungi, and many protists Different from prokaryote Plants and protists cellulose Fungi chitin Plants primary and secondary cell walls Plasmodesmata Middle lamella Primary wall Secondary wall Cell 1 Middle lamella Plasma membrane Primary wall Biophoto Associates/Photo Researchers, Inc. Secondary wall Plant cell Plasma membrane Cell µm 47

48 Extracellular matrix (ECM) Animal 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 Influence cell behavior 48

49 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Collagen Elastin Fibronectin Integrin Proteoglycan Actin filament Cytoplasm 49

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51 Cell-to-cell interactions Surface proteins give cells identity Cells make contact, read each other, and react Glycolipids most tissue-specific cell surface markers MHC proteins recognition of self and nonself cells by the immune system 51

52 Cell connections 3 categories based on function 1.Tight junction Connect the plasma membranes of adjacent cells in a sheet no leakage 2.Anchoring junction Mechanically attaches cytoskeletons of neighboring cells (desmosomes) 3.Communicating junction Chemical or electrical signal passes directly from one cell to an adjacent one (gap junction, plasmodesmata) 52

53 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tight junction Adjacent plasma membranes Tight junction proteins Intercellular space a. 2.5 µm Anchoring junction (desmosome) Microvilli Intercellular space Adjacent plasma membranes Cadherin Tight junction Cytoplasmic protein plaque b. 0.1 µm Cytoskeletal filaments anchored to plaque Adhesive junction (desmosome) Intermediate filament Communicating junction Intercellular space Communicating junction Connexon Two adjacent connexons forming an open channel between cells Channel (diameter 1.5 nm) Adjacent plasma membranes Basal lamina c. 1.4 µm a: Courtesy of Daniel Goodenough; b: Dr. Donald Fawcett/Visuals Unlimited; c: Dr. Donald Fawcett/D. Albertini/Visuals Unlimited 53

54 Plasmodesmata Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plant cells Plasmodesmata Specialized openings in their cell walls Cytoplasm of adjoining cells are connected Function similar to gap junctions in animal cells Primary Cell wall Smooth ER Middle lamella Plasma membrane Plasmodesma Central tubule Cell 1 Cell 2 54