Chapter 3: Cell Structure and
Function
Prokaryotic Microbes
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Domain: Bacteria, Archaea
Common features
o Unicellular
o No nucleus or nuclear membrane around DNA
o Smaller
o Most have cell walls
Layer Organization
o Outermost layer: Glycocalyx sitting on top of cell wall
o Cell wall sits on top of cell membrane aka plasma membrane aka
cytoplasmic membrane
External Structures of Bacterial Cells: Glycocalyx
o Structure: Gelatinous, sticky substance surrounding outside cell.
Composed of polysacs, polypeps or both
o Function: Protects against dehydration or dessication (think about
cuticle in plants)
o Capsule (protect bacteria from host defense)
 Firmly attached to cell surface of bacteria
 Function: prevent bacteria from being recognized by host,
avoid phagocfytosis by immune cells so bacteria can grow
into body and cause infection
 Since it enhances ability to cause disease, it is a virulent factor
 Said to increase virulence of microbe
 It is a global concept
o Slime Layer
 Loosely attached to cell surface
 Water soluble
 Its stickiness allows proks to attach to surfaces
 Forms biofilms (like dental plagues)
External Structures: Cell Walls
o Bacteria: has cell wall w peptidoglycan
 Peptidoglycan- sugar polymer interconnected by protein to
form strong concrete like structure. BACTERIAL ARMOR
 Many antibacterial drugs (penicillin) work by
weakening this
o Archaea: has cell walls w/o peptidoglycan and instead has other
polymers
o Gram Staining Reaction Mechanism
 Fixation: Heat fixation used to affix bacteria to slide to make
sure they don’t slide out
 Crystal Violet: Primary stain
 Iodine Treatment: Binds to crystal violet, traps it in cell
 Decolorization: apply alcohol for 25 sec
 Counter Stain safranin
o Gram Positive Cell Wall
 Will have purple stain
 Thick peptidoglycan prevents decolorization
 Contain unique polyalcohols called teichoic acids
o Gram Negative Cell Wall
 Will have pink stain
 Alcohol decolorizes this bc gneg bacteria have thin
peptidoglycan layer
 Will show pink color bc it was colorless before
 Contain bilayer membrane outside petido (OM)
 OM contains LPS which can cause fever, shock, blood
clotting
 Can make it difficult to treat disease
Gram-Positive Gram-Negative
o
Peptido
THICK
thin
o
Outer
Membrane
No
YES
o
Periplasmic
Space One
Two
o
LPS
No
Yes
o
Porin
No
yes
o
Techoic Acid
yes
no
o Acid Fast Bacteria Cell wall
 bacteria w mycolic acid (waxy lipids) up to 60% in cell walls
that help them survive desiccation.
 Cannot be stained by gram staining bc mycolic acid
prevents water soluble stains from penetrating cell wall
 SO they are stained using acid fast staining reaction
o Functions of Bacterial Cell Walls
 Provide structure + shape
 Coccus (ball), coccobacillus (long rectangular ball),
bacillus (rod), vibrio (boomerang), spirillum (spiral),
spirochete (corkscrew)
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 Pleomorphic: no cell wall w no definite shape
 Protect cell from osmotic forces
 Assist some cells in attaching to other cells
 Resisting antimicrobial drugs
External Structure: Flagella
o Atrichous- no flagella
o Peritrichous- all around
o Monotrichous- single at pole
o Lophotrichous- bunch at 1 pole
o Amphitrichous- flagella at both poles
o Amphilophotrichous- bunch of flagella at both ends
o Function: To help bacteria move
 Positive Taxis- Towards stimulus
 Negative taxis- away from stimulus
 Chemotaxis- if stimulus is chemicals
 Phototaxis- if stimulus is light
o Structure/location/motion
 Composed of 3 units- filament, hook, basal body
 Sticks out of membrane/cell wall but is not covered by
membrane
 Moves in rotary motion
 Fixed differently in gram positive and gram negative cell walls
 Endoflagella- inserted under the outer membraneof
gram negative cell wall so when flagella moves, entire
bacteria moves. Bacteria w these can infect tissues
easily
External Structure: Fimbriae
o Fimbriae are nonmotile, rodlike, sticky, bristlelike projections
o Shorter but more numerous than flagella
o Used by bacteria to stick to one another and to things in enviroimportant for biofilms
External Structure: Pili
o Pili are special types of fimbria (hollow tubes)
o Longer than fimbriae but shorter than flagella and have 1 or 2 per
cell
o Function in conjugation transfer DNA from one cell to another
(conjugation pili)
Difference between the three
o Fimbriae are shorter than pili which are shorter than flagella
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o Flagella function in movement, fimbriae function in helping bacteria
stick to things, pili function in transferring dna
External Structure: Cytoplasmic Membrane
o Phospholipid bilayer
o Fluid mosaic model for membranes
 Describes current understanding of membrane structure
 States that membrane is a mosaic of protein molecules
bobbing in a fluid bilayer of phospholipids
o Functions
 Energy storage- contains photosynthetic enzymes in
photosynthetic bacteria
 Selectively permeable barrier to limit what can pass thru
o Transport
 Passive transport- do not use energy in form of ATP bc
molecules go from high to low concentration (like diffusion)
which does not need energy
 Diffusion of small/ lipid soluble chem thru phospho
membrane
 Facilitated diffusion of dif chemicals thru nonspecific
channel protein
 Facilitated diffusion thru permease specific for one
chemical
 Osmosis- the diffusion of water thru water channel
protein or phospho bilayer
 Why are patients given saline intravenously when
dehydrated? What if they were given normal water? Giving
large amounts of pure water directly into a vein would cause
your blood cells to become hypotonic, possibly leading to
death. It would cause less on an osmotic effect. Their red
blood cells would burst if the blood becomes hypotonic
Need to be given 0.9 % saline solution – same tonicity as
blood
 Hypo/Hyper/Isotonic
 Isotonic: Cells in isotonic solutions experience no net
mvmt of water
 Hypertonic: Cells shrink bc of net mvmt of water out of
cell. When concentrations are unequal, solution w
higher concentration is hypertonic to the other
o Higher concentration of solute = lower
concentration of water
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o Cell in this would lose water and shrivel
 Hypotonic: Cells undergo net gain of water. When
concentrations are unequal, solution w lower
concentration is hypotonic to the other
o In here, cell will have higher solutes to water ratio
and expand and eventually burst
 Active Transport: require energy in the form of ATP because it
is against concentration gradient low to high
 Group translocation (ONLY IN BACTERIA): substance is
chemically altered during transport
Cytoplasm of Bacteria
o Cytosol: liquid mostly water part of cytoplasm. Contains cell’s DNA
in nucleoid
o Inclusions: contain deposits of energy rich metabolites or chemicals,
serve like fat in animals
o Nonmembranous Organelles
 Ribosomes (70s)
 Sites of protein synthesis
 Composed of Polypeps and rRNA
 Cytoskeleton
 Composed of 3 or 4 protein fibers
 Involved in cell division, cell shape, segregating DNA
molecules, moving thru enviro
 Endospores
 Unique structures made by bacteria found in cyto.
 Resistant to extreme conditions
 Defensive structures against unfavorable conditions
 Dangers of endospore-making bacteria
o Endospore containing bacteria survive heat and
grow and spoil food inside the can and cause
food poisoning.
o Those that make endospores make toxic
endotoxins
Unique Features of Archaea
o Passive and active transport similar to bacteria
o Glycocalyces, flagella, fimbriae are similar in structure and function
to bacteria but w dif macromolecules
o Hami- specialized fimbriae whose function is to attach archae to
surfaces, NOT IN BACTERIA
o NO PILI
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o Cytoplasm
 Similarities to bacteria
 70s ribosomes
 Fibrous cytoskeleton
 Circular DNA
 Differences to bacteria
 Dif rRNA and proteins in 70s ribosomes
 Dif metabolic enzymes to make RNA
 Genetic code is more similar to euks
Eukaryotic Microbes
o Uni/multicellular
o Nuclei present
o Bigger + more complex
o Some have cell walls
o Protozoa (microanimals): unicellular move thru pseudopods, cilia,
flagella
 Cilia: moves cells and substances past surface of cell
o Eukaryotic Cilia and Flagella
 Cilia- only in euks
 Flagella- in euks and proks
 Have same internal components
 Cilia is smaller and more numerous
Bacterial Flagella
Eukaryotic Flagella
Not membrane bound
(outside cell)
Rotatory Motion
Made of flagellin protein
Membrane bound (in cell)
Different basal body
structure
3 parts w hook
Side to side mvmt
Made of microtubules made of
tibulin
Different Basal body structure
2 parts w/o hook
o Eukaryotic Glycocalyx
 Not organized to form capsules
 Strengthens cell surface
 Protects against dehydration
 Function in cell to cell recognition + communication
 Help anchor animal cells to each other
o Eukaryotic Cell Wall
 Fungi, algae, plants, some protozoa have cell walls w/o
peptidoglycan
 Composed of various polysacs
 Plant cell walls have cellulose
 Fungal cell walls have cellulose, chitin, glucomannan
 Algal cell walls have variety of polysacs
o Eukaryotic cytoplasmic membrane
 All have membrane which are fluid mosaic of phospholipids
and proteins similar to cell membranes
 Also have steroid lipids to help maintain fluidity
 Also contain regions of lipids + proteins called membrane rafts
o Transport Processes in Euk Cytoplasmic Membranes
 Passive + active transport similar to proks
 Endocytosis + exocytosis: Unique to euks
 Endocytosis- substances surrounded by pseudopods
and brought into cell
 Exocytosis- vesicles w substances are fused w
cytoplasmic membrane, dumping their contents to the
outside
o Nonmembranous eukaryotic organelles
 Ribosomes 80s: larger and dif than prok, made up of polypep
and rRNA and sites of protein synthesis
 Cytoskeleton: skeleton of cell, extensive network of fibers +
tubules, anchors organelles, basic shape of cell
 Centrioles: involved in formation of flagella + cilia, made of
microtubules
 Centrosome: region where centrioles are found, only seen in
animal cells
 Internal membranes (nuc, ER, golgi, lyso, peroxis, vacs,
vesivles, mitoch) are absent in proks
 Cell wall (archaea): present in most w/o peptido
 Cell wall (bacteria): present in most w/ peptide
 Cell wall (euks): Present in plants algae fungi
 Endosymbiotic Theory
o Euks formed from union of small aerobic proks and photosynthetic
proks w larger anaerobic euks
o Smaller proks became internal parasites
 They lost ability to live on own
 Aerobic proks formed into mitochondria
 Photosynthetic proks evolved into chlorplasts