Cell structure and function for microbiologists

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Cell structure and function for
microbiologists Prokaryotes Eukaryotes Both
have the same types of biological
molecules metabolism, protein synthesis, ATP
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Eukaryotes have organelles

• Much larger more complex than prokaryotes
• Processes compartmentalized into organelles
• Nucleus
• Protein synthesis (ribosomes, RER, Golgi)
• Mitochondria chloroplasts
• Lysosomes
• Plasma membranes have different modifications
• Cytoskeleton

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Eukaryotes may be multicellular

• Cells may be variable within the organism
• Tissues
• Organs
• See table 3.7 on p. 72

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Prokaryotes Have no nucleus genome is
circular No histones No membrane-bound
organelles Cell wall usually contains
peptidoglycan (cell walls are more
complex) Divide by binary fission
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Prokaryotes include eubacteria and archaea How
do you tell them apart? Theyre all
small! morphology chemical composition nutritio
nal and energy requirements
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Typical shapes of bacteria
Most bacteria retain a particular shape a
few are pleiomorphic
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Characteristic grouping (or not grouping)
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Even in groups, bacteria tend to be
single- celled in structure and behavior Some
have colonial traits Well-studied example
myxobacteria hunting colonies fruiting
bodies Etc.
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Typical prokaryotic structures
Working from the outside in
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Extracellular components Protection dehydration
immune mechanisms Attachment Glycocalyx-
polysaccharide, protein capsule if
organized slime layer if not May contribute to
virulence
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Some bacteria are motile (due to
flagella) Bacteria vary in the way flagella are
attached How they move running, tumbling,
swarming Can move toward or away from light
or chemical stimuli Flagellin protein is unique
to prokaryotes
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Cocci do not have flagella
Peritrichous monotrichous (or amphi, or
lophotrichous
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Pili- attachment motility conjugation
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Cell membrane structure is similar in
structure and function to that of
eukaryotes Phospholipid bilayer (everything
moves through it, since there are no
organelles) carrier proteins generally
involve proton motive force (i.e, require energy
and moving against the concentration gradient)
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Cell wall- hallmark of prokaryotes Their
reaction with Gram stain allows bacterai to be
divided into two groups Positive-lots of
peptidoglycan Negative- thin layer, with an
outer membrane and periplasmic space in
between Many secreted proteins are found here
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Structure of peptidoglycan
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Gram-positive cell wall
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Outer membrane is made of lipopolysaccharide (LPS
) Porins allow molecules to pass through outer
membrane LPS is protective lipid A- strong
inflammatory response (endotoxin) O-linked
polysaccharide- antigenic
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Significance of Gram-positive vs
Gram-negative antibiotic sensitivity sensitivit
y to lysozyme reaction with Gram
reagents crystal violet iodine alcohol saf
ranin
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Mycoplasma do not have a cell wall Lots of
variety in archaea- but none have peptidoglycan
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Internal components Nucleoid- with single,
circular, supercoiled DNA molecule Many
bacteria have plasmids small, extrachromosomal,
circular piece of DNA genes present are
usually not required but may be
advantageous (antibiotic resistance, resistance
to metals) Now used for genetic engineering
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Ribosomes Involved in protein synthesis Prokaryo
tic ribosomes are smaller than eukaryotic (70S
vs 80S) Some antibiotics bind to the 70S
ribosome How does that affect bacteria?
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No membrane-bound organelles Some have storage
granules Some aquatic bacteria have gas
vesicles Some have endospores (soil bacteria)
that enable them to lie dormant
under unfavorable conditions NOT a
reproductive structure
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Summary

• Eukaryotes have membrane-bound organelles
• Eukaryotes may be multicellular with highly
  specialized cells
• Prokaryotes have simple shapes and are classified
  according to their morphology
• Certain structures are unique to prokaryotes