Start here_ch03_lecture

Copyright © 2009 Pearson Education Inc., publishing as Pearson Benjamin Cummings

Lecture prepared by Mindy Miller-Kittrell, University of Tennessee, Knoxville

M I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITION

Chapter 3 Cell Structure and Function


Processes of Life

• Growth• Reproduction• Responsiveness• Metabolism


Processes of Life


Prokaryotic & Eukaryotic Cells: An Overview

[INSERT FIGURE 3.1]



• Prokaryotes– Do not have membrane surrounding their DNA; lack a nucleus– Lack various internal structures bound with phospholipid

membranes– Are small, ~1.0 µm in diameter– Have a simple structure– Composed of bacteria and archaea



[INSERT FIGURE 3.2]



• Eukaryotes– Have membrane surrounding their DNA; have a nucleus– Have internal membrane-bound organelles– Are larger, 10-100 µm in diameter– Have more complex structure– Composed of algae, protozoa, fungi, animals, and plants



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External Structures of Prokaryotic Cells

• Glycocalyces

– Gelatinous, sticky substance surrounding the outside of the cell– Composed of polysaccharides, polypeptides, or both



• Two Types of Glycocalyces– Capsule

– Composed of organized repeating units of organic chemicals– Firmly attached to cell surface– Protects cells from drying out– May prevent bacteria from being recognized and destroyed by host

– Slime layer– Loosely attached to cell surface– Water soluble– Protects cells from drying out– Sticky layer that allows prokaryotes to attach to surfaces



[INSERT FIGURE 3.5]



Animation: MotilityAnimation: Motility



• Flagella– Are responsible for movement– Have long structures that extend beyond cell surface– Are not present on all prokaryotes



• Flagella– Structure

– Composed of filament, hook, and basal body– Flagellin protein (filament) deposited in a helix at the

lengthening tip– Base of filament inserts into hook– Basal body anchors filament and hook to cell wall by a rod

and a series of either two or four rings of integral proteins– Filament capable of rotating 360º



Animation: Flagella StructureAnimation: Flagella Structure



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Animation: Flagella ArrangementAnimation: Flagella Arrangement



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• Flagella– Function

– Rotation propels bacterium through environment– Rotation reversible, can be clockwise or counterclockwise– Bacteria move in response to stimuli (taxis)

– Runs – Tumbles



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Animation: Flagella MovementAnimation: Flagella Movement



• Fimbriae and Pili– Rod-like proteinaceous extensions



• Fimbriae – Sticky, bristlelike projections– Used by bacteria to adhere to one another, to hosts, and

to substances in environment– Shorter than flagella– May be hundreds per cell– Serve an important function in biofilms



[INSERT FIGURE 3.10]



• Pili– Tubules composed of pilin– Also known as conjugation pili – Longer than fimbriae but shorter than flagella– Bacteria typically only have one or two per cell– Mediate the transfer of DNA from one cell to another

(conjugation)





Prokaryotic Cell Walls

• Provide structure and shape and protect cell from osmotic forces• Assist some cells in attaching to other cells or in eluding antimicrobial

drugs• Not present in animal cells, so can target cell wall of bacteria with

antibiotics• Bacteria and archaea have different cell wall chemistry


Prokaryotic Cell Wall

• Bacterial Cell Walls– Most have cell wall composed of peptidoglycan– Peptidoglycan is composed of sugars, NAG, and NAM– Chains of NAG and NAM attached to other chains by tetrapeptide

crossbridges– Bridges may be covalently bonded to one another– Bridges may be held together by short connecting chains of

amino acids– Scientists describe two basic types of bacterial cell walls: Gram-

positive and Gram-negative









• Bacterial Cell Walls– Gram-positive cell walls

– Relatively thick layer of peptidoglycan– Contain unique polyalcohols called teichoic acids

– Some covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane

– Retain crystal violet dye in Gram staining procedure; so appear purple

– Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation



[INSERT FIGURE 3.14a]



• Bacterial Cell Walls– Gram-negative 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



[INSERT FIGURE 3.14b]



• Archaeal Cell Walls– Do not have peptidoglycan – Contains variety of specialized polysaccharides and proteins– Gram-positive archaea stain purple – Gram-negative archaea stain pink


Prokaryotic Cytoplasmic Membranes

• Structure– Referred to as phospholipid bilayer; composed of lipids and

associated proteins– Approximately half composed of proteins that act as recognition

proteins, enzymes, receptors, carriers, or channels– Integral proteins – Peripheral proteins – Glycoproteins

– Fluid mosaic model describes current understanding of membrane structure






• Function– Energy storage– Harvest light energy in photosynthetic prokaryotes– Selectively permeable– Naturally impermeable to most substances– Proteins allow substances to cross membrane

– Occurs by passive or active processes– Maintain concentration and electrical gradient

– Chemicals concentrated on one side of the membrane or the other– Voltage exists across the membrane






• Function– Passive processes

– Diffusion– Facilitated diffusion – Osmosis

– Isotonic solution – Hypertonic solution – Hypotonic solution












• Function– Active processes

– Active transport– Utilize permease proteins and expend ATP– Uniport – Antiport – Symport

– Group translocation– Substance chemically modified during transport






Animation: Active Transport OverviewAnimation: Active Transport Overview



Animation: Active Transport TypesAnimation: Active Transport Types






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Cytoplasm of Prokaryotes

• Cytosol – liquid portion of cytoplasm

• Inclusions – may include reserve deposits of chemicals

• Endospores – unique structures produced by some bacteria that are a defensive strategy against unfavorable conditions





• Nonmembranous Organelles

– Ribosomes – sites of protein synthesis

– Cytoskeleton – plays a role in forming the cell’s basic shape





External Structure of Eukaryotic Cells

• Glycocalyces– Never as organized as prokaryotic capsules– Help anchor animal cells to each other– Strengthen cell surface– Provide protection against dehydration– Function in cell-to-cell recognition and communication


Eukaryotic Cell Walls & Cytoplasmic Membranes

• Fungi, algae, plants, and some protozoa have cell walls but no glycocalyx

• Composed of various polysaccharides– Cellulose found in plant cell walls– Fungal cell walls composed of cellulose, chitin, and/or

glucomannan– Algal cell walls composed of cellulose, proteins, agar,

carrageenan, silicates, algin, calcium carbonate, or a combination of these






• All eukaryotic cells have cytoplasmic membrane• Are a fluid mosaic of phospholipids and proteins• Contain steroid lipids to help maintain fluidity• Contain regions of lipids and proteins called membrane rafts• Control movement into and out of cell

– Use diffusion, facilitated diffusion, osmosis, and active transport– Perform endocytosis; phagocytosis if solid substance and

pinocytosis if liquid substance– Exocytosis enables substances to be exported from cell






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Cytoplasm of Eukaryotes



• Flagella– Structure and arrangement

– Shaft composed of tubulin arranged to form microtubules– “9 + 2” arrangement of microtubules in all flagellated

eukaryotes– Filaments anchored to cell by basal body; no hook– Basal body has “9 + 0” arrangement of microtubules– May be single or multiple; generally found at one pole of cell



• Flagella– Function

– Do not rotate, but undulate rhythmically



[INSERT FIGURE 3.28a & b]



• Cilia– Shorter and more numerous than flagella– Composed of tubulin in “9 + 2” and “9 + 0” arrangements– Coordinated beating propels cells through their environment– Also used to move substances past the surface of the cell



[INSERT FIGURE 3.27c]



• Other Nonmembranous Organelles– Ribosomes

– Larger than prokaryotic ribosomes (80S versus 70S)– Composed of 60S and 40S subunits

– Cytoskeleton– Extensive – Functions

– Anchors organelles– Cytoplasmic streaming and movement of organelles– Movement during endocytosis and amoeboid action– Produces basic shape of the cell

– Made up of tubulin microtubules, actin microfilaments, and intermediate filaments






• Other Nonmembranous Organelles– Centrioles and centrosome

– Centrioles play a role in mitosis, cytokinesis, and in formation of flagella and cilia

– Centrioles composed of “9 + 0” arrangement of microtubules– Centrosome is region of cytoplasm where centrioles are

found






• Membranous Organelles– Nucleus

– Often largest organelle in cell– Contains most of the cell’s DNA– Semi-liquid portion called nucleoplasm– One or more nucleoli present in nucleoplasm; RNA

synthesized in nucleoli– Nucleoplasm contains chromatin – masses of DNA

associated with histones– Surrounded by nuclear envelope – double membrane

composed of two phospholipid bilayers– Nuclear envelope contains nuclear pores






• Membranous Organelles– Endoplasmic reticulum

– Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope

– Functions as transport system– Two forms

– Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis

– Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; transports proteins produced by ribosomes






• Membranous Organelles– Golgi body

– Receives, processes, and packages large molecules for export from cell

– Packages molecules in secretory vesicles that fuse with cytoplasmic membrane

– Composed of flattened hollow sacs surrounded by phospholipid bilayer

– Not in all eukaryotic cells






• Membranous Organelles– Lysosomes, peroxisomes,vacuoles, and vesicles

– Store and transfer chemicals within cells– May store nutrients in cell– Lysosomes contain catabolic enzymes – Peroxisomes contain enzymes that degrade poisonous

wastes









• Membranous Organelles– Mitochondria

– Have two membranes composed of phospholipid bilayer– Produce most of cell’s ATP– Interior matrix contains 70S ribosomes and circular molecule of

DNA






• Membranous Organelles– Chloroplasts

– Light-harvesting structures found in photosynthetic eukaryotes– Have two phospholipid bilayer membranes and DNA– Have 70S ribosomes






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• Endosymbiotic Theory– Eukaryotes formed from union of small aerobic prokaryotes with

larger anaerobic prokaryotes– smaller prokaryotes became internal parasites

– Parasites lost ability to exist independently; retained portion of DNA, ribosomes, and cytoplasmic membranes

– Larger cell became dependent on parasites for aerobic ATP production

– Aerobic prokaryotes evolved into mitochondria– Similar scenario for origin of chloroplasts

– Not universally accepted



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