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Flashcards in IntroMicro Deck (39)
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Microbes are Everywhere

Microbiology-the study of ________, ___________________________.

Microbes are ____________

Microbes may be ____ or ____

Microbes exist _____, or _____

¡Microbiology-the study of microorganisms, single-celled microscopic organisms.
¡Microbes are independent life-forms
¡ Microbes may be prokaryotic, or eukaryotic
¡Microbes exist free living in the environment, or colonize a host.


It’s a Microbial World

Microbes  live in large numbers in ___ and ____

____ ____, and are important for ____ ____


Saprophytic bacteria

¡Microbes  live in large numbers in soil and water
¡Metabolically diverse, and are important for nutrient cycling

Break down dead material


The original life on Earth

¡Microbes are the __________________
¡Bacteria ________________.

¡Microbes are the oldest forms of life on Earth
¡Bacteria created an oxygenated atmosphere


The Microbes Within

¡Bacteria can act as____

_____: ____


¡Bacteria can act as symbionts:
§Other microbes


It’s the Microbiome! = _____= ______

¡Important for ____
¡Can cause____

¡The Human Flora
¡The bacteria that live on us and in us
¡Important for health
¡Can cause disease
§Taking antibiotics for an infection
§Destroying the gut microbiome




Procaryotes vs Eucaryotes


much smaller than eukaryotes, which are




Size: 0.1-3 microm 

much smaller than eukaryotes, which are  > 5 microm

No membrane-bound organelles

no nucleus, mito-chondria, endoplasmic reticulum, Golgi, etc., which are characteristic of eukaryotes


Bacterial genomes

•____(most eukaryotes are ____)
•typically ___ chromosome of ____-stranded, ________, _____ DNA
•not contained by a ____ ____ as in eukaryotes
•DNA is___________ in an area called the ____
•organized in ____ coiled loops due to associated ___ and ____



•haploid (most eukaryotes are diploid)
•typically one chromosome of double-stranded, super-coiled, circular DNA
•not contained by a nuclear membrane as in eukaryotes
•DNA is free in cytoplasm in an area called the nucleoid
•organized in 40-50 coiled loops due to associated RNA and proteins


Bacteria may contain plasmids

____ ____ ___-_____ DNA
•may confer ____ ____
_____/____ genes
•--i.e. ___ ____

•small circular extra-chromosomal DNA
•may confer antibiotic resistance
•toxicity/virulence genes
•--i.e. anthrax toxins


Bacterial genes

•do not contain ____

_____: _________________and ______________
•_________:  ________________


Bacterial genes

•do not contain introns

•operons: functionally related genes tandemly arrayed and co-transcribed to yield a polycistronic mRNA

•transcription-translation coupling:  translation begins as mRNA being transcribed


Bacterial Cell Membrane 
Cytoplasmic membrane
▪Lipid bilayer with_______________
▪Forms a ___ ___ between the____ and ____
▪____ of ____

  • ­_____
  • ­_______
  • ­_______

▪Gram + bacteria have ___ membrane, Gram – bacteria have ___

§Cytoplasmic membrane
▪Lipid bilayer with embedded membrane proteins
▪Forms a selective barrier between the cytoplasm and environment
▪Generation of gradients
­Proton motive force
­Concentration of nutrients
­Exclusion of wastes/toxins
▪Gram + bacteria have one membrane, Gram – bacteria have two


Cell Wall

Cell Wall

•Located just outside the __________
•Gives bacterium ___ and ___
•Composed of ____

  • •Only found in ____

•Protects against ____ ____
•Different_____ in Gram – and Gram + bacteria

Cell Wall

•Located just outside the cytoplasmic membrane
•Gives bacterium rigidity and shape
•Composed of peptidoglycan
•Only found in prokaryotes
•Protects against osmotic lysis
•Different thickness in Gram – and Gram + bacteria


Cell Wall Peptidoglycan
•____  ____ chains ___-____ by ___ ____ ____

•Polysaccharide chain:
•repeating ____ of _______ and________
•cleaved by ___ ____yielding a ____ which____ unless _____ ___

•Cross-linking peptides
•always linked to ___ ___via ____
•____ ___-____ _______ catalyze _____________

  • •called _______________ because they are targets for___ and other ______


•Linear polysaccharide chains cross-linked by short peptide chains

•Polysaccharide chain:
•repeating disaccharide of N-acetylmuramic acid (M) and N-acetylglucosamine (G)
•cleaved by host lysozyme yielding a spheroplast which lyses unless osmotically stabilized

•Cross-linking peptides
•vary with species
•always linked to carbohydrate chains via muramic acid (M).
•Cytoplasmic membrane-bound transpeptidases catalyze the cross-linking reactions
•called penicillin-binding proteins (PBPs) because they are targets for penicillin and other b-lactam antibiotics.



Gram Positive Bacteria

•____ _____ wall (__-__Å)
•consists mainly of ________
•also contains _____ and _____

  • •polymers of ____ (or ____) and ____
  • •teichoic acid is _____________
  • •lipoteichoic acid is _________________ by _________________

•thick multilayer wall (150-500 Å)
•consists mainly of peptidoglycan
•also contains teichoic and lipoteichoic acids
•polymers of glycerol (or ribitol) and phosphate
•teichoic acid is cross-linked to peptidoglycan
•lipoteichoic acid is anchored to the cytoplasmic membrane by covalently attached fatty acid


Gram Negative Bacteria

¡Peptidoglycan layer


¡Outer membrane
•lies ____________
•contains ___ ____ ____ ____, which allow ________________
•_________ constitutes the ___ ___

¡Periplasmic space
•bounded by _____ and ____
•contains a variety of ____ ____s including ____ _____ (e.g., ______)


¡Peptidoglycan layer
•thin; lies outside the cytoplasmic membrane

¡Outer membrane
•lies outside the peptidoglycan layer
•contains pore-forming porin proteins, which allow entry of small hydrophilic molecules
•lipopolysaccharide (LPS) constitutes its outer leaflet

¡Periplasmic space
•bounded by cytoplasmic and outer membranes
•contains a variety of hydrolytic enzymes including virulence factors (e.g., collagenase)



Lipopolysaccharide (LPS)

•occurs in the ___ ____ of the___ ____of Gram ___ bacteria.
•also known as ____

•a powerful ____ of the ____ ____
•endotoxin activity due to ___ ___

  • •___ ____
  • •useful for _______ _____

•occurs in the outer leaflet of the outer membrane of Gram(-) bacteria.
•also known as endotoxin.

•a powerful stimulator of the immune response
•endotoxin activity due to lipid A
•useful for serologic identification


Cell Wall: Peptidoglycan & the Gram Stain

•Gram(+) bacteria have a ____peptidoglycan cell wall, which ___________ (a __________complex)

•Gram(–) bacteria have a ____ peptidoglycan layer, which allows the stain to be ____ ____away


•Gram(+) bacteria have a thick peptidoglycan cell wall, which traps the Gram stain (a crystal violet-iodine complex)

•Gram(–) bacteria have a thin peptidoglycan layer, which allows the stain to be readily washed away



External Appendages



§ Flagella
§ Pili


Cell Wall Morphology

____ and ___ 



Bacterial Reproduction and Growth

____ reprod via ____ ____
____ offspring

Cell division

•asexual reproduction via binary fission
•Clonal offspring


Genetic Transfer 

¡Transfer of DNA between bacteria occurs ____________



¡Bacteria can share _____________by genetic transfer (___ ___)

¡Transfer of DNA between bacteria occurs separately from cell division
¡Bacteria can share favorable new genes by genetic transfer (antibiotic resistance)


Growth Phases

•Lag phase: 
•period of ____ to ____ ____

•Log or exponential phase:
____ ___
___ ____ is characteristic of the ___

•Stationary phase:
•___ or____become ____ or ____ metabollic products _____
•cell division rate __ cell death rate

•Death phase:
•cell death rate_ cell division rate

•Lag phase: 
•period of adaptation to new condition

•Log or exponential phase:
•optimal growth
•doubling time is characteristic of the strain

•Stationary phase:
•nutrients or oxygen become limiting or toxic metabolic products accumulate
•cell division rate = cell death rate

•Death phase:
•cell death rate > cell division rate



Growth Rate is Dependent on Environmental Conditions

¡Bacteria occupy diverse habitats, and have ____ ____ of ___ and ____ for ____
Resources: __ ___ ____ _____ _____ ____. macro, micro, donor, acceptor, C N 
Conditions: ___ ___ ___ ___ ___ ____ light T pH osmolarity O2water

¡Bacteria occupy diverse habitats, and have favored sources of energy and conditions for growth
Resources: C, N, macronutrients, micronutrients, O2 (e acceptor), inorganic e donor
Conditions: T, pH, water, O2, Light, Osmotic conditions


Bacterial Oxygen Tolerance

•Strict aerobes
•restricted to using ___ ____
•can only use ___ as ______
•lack ________

•Facultative anaerobes
•capable of _____ ____in the presence of O2
•use either ____ or _____in its absence

•Strict anaerobes
•lack ___ ___ ____
•depend on ____ to generate energy
•______ ____(some ___ ____) in ___ usually due to lack of _____ ____ and/or ____

•Aerotolerant anaerobes
•lack ___ ___ ____
•depend on ____
•tolerate ___ but __________, have ___ and/or ____

•Microaerophilic bacteria
•require a ____ amount of oxygen, but too much is____


•Strict aerobes
•restricted to using aerobic respiration
•can only use O2 as final electron acceptor
•lack enzymes for fermentation

•Facultative anaerobes
•capable of aerobic respiration in the presence of O2
•use either anaerobic respiration or fermentation in its absence

•Strict anaerobes
•lack respiratory chain enzymes
•depend on fermentation to generate energy
•cannot grow (some cannot survive) in O2 usually due to lack of superoxide dismutase(SOD) and/or catalase

•Aerotolerant anaerobes
•lack respiratory chain enzymes
•depend on fermentation
•tolerate O2 but do not use it, have catalase and/or SOD

•Microaerophilic bacteria
•require a small amount of oxygen, but too much is toxic.



There are more bacterial cells in the human body
than there are human cells.

~10__ human cells

~10__ bacterial cells


There are more bacterial cells in the human body
than there are human cells.

~1013 human cells

~1014 bacterial cells



Host-Microbe Interactions


not _____

___ ____

___ the host

___ ____
___ associated, with no _____

Opportunistic pathogens
Can cause ___ in ___ ____

Frank pathogens
Can cause ___ in ___ ____

nnot found in association with a host
nSymbiotic organisms
nbenefit the host
nCommensal organisms
n host-associated, with no apparent negative effects
nOpportunistic pathogens
nCan cause disease in compromised hosts
nFrank pathogens
nCan cause disease in immunocompetent hosts


Human Symbiotic Bacteria

____ bacteria participate in ____
___ ____ broken down into ____ and ___ ____ ___
____ of __ ____ in gut ___

¡Gut bacteria participate in digestion
§Complex carbohydrates broken down into mono-saccharides and volatile fatty acids
§“Maturing” of gene expression in gut mucosa 


Human Commensal Bacteria

“___ ____”
§No ______
¡May protect the host by ______ ___ ___ by _____.

¡Most bacteria that colonize humans are considered commensal
§“Normal Flora”
§No direct measurable benefit
¡May protect the host by “excluding” pathogenic bacteria by competition


Opportunistic pathogens

¡Members of the ____ ____ may become pathogenic
§Host defenses are ____

  • ▪Enter normally __ ____ through___
  • ▪Host___ ____are compromised
    • ____
  • ▪____ host physiology


¡Members of the normal flora may become pathogenic
§Host defenses are compromised
▪Enter normally sterile tissues through injury
▪Host immune defenses are compromised
▪Imbalanced host physiology