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Cell Structure and Function
Chapter 3 Cell Structure and Function
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Cell Morphology 3 main shapes Rod (bacillus) Sphere (coccus) Spiral (spirilla)
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Processes of Life Growth Reproduction Responsiveness
Metabolism—chemical reactions in the cell. Building up and breaking down molecules. © 2012 Pearson Education Inc. 3
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Prokaryotic and Eukaryotic Cells: An Overview
Prokaryotes Lack nucleus Lack various internal structures bound with phospholipid membranes Are small (~1.0 µm in diameter) micrometers Have a simple structure Include bacteria and archaea © 2012 Pearson Education Inc. 4
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Figure 3.2 Typical prokaryotic cell
Inclusions Ribosome Cytoplasm Nucleoid Flagellum Glycocalyx Cell wall Cytoplasmic membrane 5
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Prokaryotic and Eukaryotic Cells: An Overview
Eukaryotes Have nucleus Have internal membrane-bound organelles Are larger (10–100 µm in diameter) Have more complex structure Include algae, protozoa, fungi, animals, and plants © 2012 Pearson Education Inc. 6
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Figure 3.3 Typical eukaryotic cell
Nuclear envelope Nuclear pore Nucleolus Lysosome Mitochondrion Centriole Secretory vesicle Golgi body Cilium Transport vesicles Ribosomes Rough endoplasmic reticulum Smooth endoplasmic reticulum Cytoplasmic membrane Cytoskeleton 7
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Figure 3.4 Approximate size of various types of cells
Virus Orthopoxvirus 0.3 m diameter Bacterium Staphylococcus 1 m diameter Chicken egg 4.7 cm diameter (47,000 m)* Parasitic protozoan Giardia 14 m length *Actually, the inset box on the egg would be too small to be visible. (Width of box would be about mm.) 8
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External Structures of Bacterial Cells
Glycocalyces Gelatinous, sticky substance surrounding the outside of the cell Composed of polysaccharides, polypeptides, or both © 2012 Pearson Education Inc. 9
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External Structures of Bacterial Cells
Two Types of Glycocalyces Capsule Firmly attached to cell surface May prevent bacteria from being recognized by host Slime layer Loosely attached to cell surface Sticky layer allows prokaryotes to attach to surfaces © 2012 Pearson Education Inc. 10
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Figure 3.5 Glycocalyces-overview
Glycocalyx (capsule) Glycocalyx (slime layer) 11
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External Structures of Bacterial Cells
Flagella Are responsible for movement Have long structures that extend beyond cell surface Are not present on all bacteria © 2012 Pearson Education Inc. 12
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Figure 3.7 Micrographs of basic arrangements of bacterial flagella-overview
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Figure 3.8 Axial filament-overview
Endoflagella rotate Axial filament rotates around cell Axial filament Outer membrane Cytoplasmic membrane Spirochete corkscrews and moves forward Axial filament 14
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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—phototaxis or chemotaxis) Runs Tumbles © 2012 Pearson Education Inc. 15
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Figure 3.9 Motion of a peritrichous bacterium
Attractant Run Tumble Run Tumble 16
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External Structures of Bacterial Cells
Fimbriae and Pili Rodlike proteinaceous extensions © 2012 Pearson Education Inc. 17
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External Structures of Bacterial Cells
Fimbriae Sticky, bristlelike projections Used by bacteria to adhere to one another, to hosts, and to substances in environment Shorter than flagella Serve an important function in biofilms © 2012 Pearson Education Inc. 18
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Figure Fimbriae Flagellum Fimbria 19
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External Structures of Bacterial Cells
Pili Special type of fimbria Also known as conjugation pili Longer than other fimbriae but shorter than flagella Bacteria typically have only one or two per cell Mediate the transfer of DNA from one cell to another (conjugation) © 2012 Pearson Education Inc. 20
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Figure Pili Conjugation pilus 21
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Bacterial Cell Walls 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 Cell wall of bacteria can be targeted with antibiotics Give bacterial cells characteristic shapes Composed of peptidoglycan Scientists describe two basic types of bacterial cell walls, Gram-positive and Gram-negative © 2012 Pearson Education Inc. 22
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Figure 3.12 Bacterial shapes and arrangements-overview
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Gram-Positive Bacterial Cell Walls
Relatively thick layer of peptidoglycan Appear purple following Gram staining procedure © 2012 Pearson Education Inc. 24
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Gram-positive cell wall
Figure 3.15a 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 25
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Gram-Negative Bacterial Cell Walls
Have only a thin layer of peptidoglycan Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS) May be impediment to the treatment of disease Appear pink following Gram staining procedure © 2012 Pearson Education Inc. 26
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Gram-negative cell wall
Figure 3.15b Comparison of cell walls of Gram-positive and Gram-negative bacteria Porin Outer membrane of cell wall Porin (sectioned) Peptidoglycan layer of cell wall Periplasmic space Cytoplasmic membrane Gram-negative cell wall Phospholipid layers n Lipopolysaccharide (LPS) O side chain (varies In length and composition) Integral proteins Core polysaccharide Lipid A (embedded in outer membrane) Fatty acid 27
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Comparison of Gram positive and Gram negative cells
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Bacterial Cytoplasmic Membranes
Structure Referred to as phospholipid bilayer Composed of lipids and associated proteins Fluid mosaic model describes current understanding of membrane structure © 2012 Pearson Education Inc. 29
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Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer
Head, which contains phosphate (hydrophilic) Phospholipid Tail (hydrophobic) Integral proteins Cytoplasm Integral protein Phospholipid bilayer Peripheral protein Integral protein 30
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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 gradient © 2012 Pearson Education Inc. 31
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Bacterial Cytoplasmic Membranes
Function Passive processes Diffusion Facilitated diffusion Osmosis Active processes Active transport © 2012 Pearson Education Inc. 32
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Isotonic solution Hypertonic solution Hypotonic solution
Figure Effects of isotonic, hypertonic, and hypotonic solutions on cells-overview Cells without a wall (e.g., mycoplasmas, animal cells) H2O H2O H2O Cell wall Cell wall Cells with a wall (e.g., plants, fungal and bacterial cells) H2O H2O H2O Cell membrane Cell membrane Isotonic solution Hypertonic solution Hypotonic solution 33
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Cytosol – Liquid portion of cytoplasm
Cytoplasm of Bacteria Cytosol – Liquid portion of cytoplasm Endospores – Unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions © 2012 Pearson Education Inc. 34
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Nonmembranous Organelles
Cytoplasm of Bacteria Nonmembranous Organelles Ribosomes Sites of protein synthesis 70S—consists of 50S large subunit and 30S small subunit. Cytoskeleton Plays a role in forming the cell’s basic shape © 2012 Pearson Education Inc. 35
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External Structures of Archaea
Glycocalyces Adhere cells to one another and inanimate objects Flagella Fimbriae and Hami Many archaea have fimbriae Some make fimbriae-like structures called hami Function to attach archaea to surfaces © 2012 Pearson Education Inc. 36
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Figure Archaeal hami Hamus Grappling hook Prickles 37
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Archaeal Cell Walls and Cytoplasmic Membrane
Most archaea have cell walls Do not have peptidoglycan Contain variety of specialized polysaccharides and proteins All archaea have cytoplasmic membranes Maintain chemical gradients Control import and export of substances from the cell Lipids lack phosphate (not phospholipids). © 2012 Pearson Education Inc. 38
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Figure 3.27 Representative shapes of archaea-overview
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Cytoplasm of Archaea Archaeal cytoplasm similar to bacterial cytoplasm
Have 70S ribosomes Fibrous cytoskeleton Circular DNA Archaeal cytoplasm also differs from bacterial cytoplasm Different ribosomal proteins Different metabolic enzymes to make RNA © 2012 Pearson Education Inc. 40
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External Structure of Eukaryotic Cells
Glycocalyces Never as organized as prokaryotic capsules Help anchor animal cells to each other Provide protection against dehydration © 2012 Pearson Education Inc. 41
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Eukaryotic Cell Walls Fungi, algae, plants, and some protozoa have cell walls Composed of various polysaccharides Plant cell walls composed of cellulose Fungal cell walls usually composed of chitin. Algal cell walls composed of a variety of polysaccharides. © 2012 Pearson Education Inc. 42
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Eukaryotic Cytoplasmic Membranes
All eukaryotic cells have cytoplasmic membrane Are a fluid mosaic of phospholipids and proteins Contain steroid lipids to help maintain fluidity Control movement into and out of cell © 2012 Pearson Education Inc. 43
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Figure 3.30 Endocytosis-overview
Pseudopodium 44
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Cytoplasm of Eukaryotes
Flagella Structure and arrangement Differ structurally and functionally from prokaryotic flagella Function Do not rotate but undulate rhythmically © 2012 Pearson Education Inc. 45
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Figure 3.31a Eukaryotic flagella and cilia
Flagellum 46
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Figure 3.31b Eukaryotic flagella and cilia
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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 © 2012 Pearson Education Inc. 48
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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 © 2012 Pearson Education Inc. 49
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