Cell Structure and Function Chapter 3 Cell Structure and Function

Cell Morphology 3 main shapes Rod (bacillus) Sphere (coccus) Spiral (spirilla)

Processes of Life Growth Reproduction Responsiveness Metabolism—chemical reactions in the cell. Building up and breaking down molecules. © 2012 Pearson Education Inc. 3

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

Figure 3.2 Typical prokaryotic cell Inclusions Ribosome Cytoplasm Nucleoid Flagellum Glycocalyx Cell wall Cytoplasmic membrane 5

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

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

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 0.002 mm.) 8

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

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

Figure 3.5 Glycocalyces-overview Glycocalyx (capsule) Glycocalyx (slime layer) 11

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

Figure 3.7 Micrographs of basic arrangements of bacterial flagella-overview 13

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

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

Figure 3.9 Motion of a peritrichous bacterium Attractant Run Tumble Run Tumble 16

External Structures of Bacterial Cells Fimbriae and Pili Rodlike proteinaceous extensions © 2012 Pearson Education Inc. 17

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

Figure 3.10 Fimbriae Flagellum Fimbria 19

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

Figure 3.11 Pili Conjugation pilus 21

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

Figure 3.12 Bacterial shapes and arrangements-overview 23

Gram-Positive Bacterial Cell Walls Relatively thick layer of peptidoglycan Appear purple following Gram staining procedure © 2012 Pearson Education Inc. 24

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

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

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

Comparison of Gram positive and Gram negative cells

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

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

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

Bacterial Cytoplasmic Membranes Function Passive processes Diffusion Facilitated diffusion Osmosis Active processes Active transport © 2012 Pearson Education Inc. 32

Isotonic solution Hypertonic solution Hypotonic solution Figure 3.20 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

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

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

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

Figure 3.26 Archaeal hami Hamus Grappling hook Prickles 37

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

Figure 3.27 Representative shapes of archaea-overview 39

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

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

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

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

Figure 3.30 Endocytosis-overview Pseudopodium 44

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

Figure 3.31a Eukaryotic flagella and cilia Flagellum 46

Figure 3.31b Eukaryotic flagella and cilia 47

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

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