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Flashcards in Microbiology - 2 - Bacteria Deck (14):
1

What are the basic shapes of bacterial cells? 

  1. Rod
    • Single = Bacillus
    • Chain = Steptobacillus
      • can be straigh or curved
  2. Sphere 
    • singular = coccus
    • plural = cocci
      • clusters = staphylococcus
      • chain = streptococcus
  3. Spiral 
    • ​can be rigid or flexible & undulating
      • Vibrio = comma shaped
      • Spirillum = wavy
      • Spirochete = spiral
  4. Other
    • square
    • star
    • filamentous
    • appendaged

 

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2

What are the structures &  functions of bacterial cells? 

Envelope

  • Capsule - polysaccharide
    • hydrophilic gel = discrete layer = capsule
    • slime layer = amorphous
      • provides general protection from immune system
  • Cell Wall - Gram (-) / (+) 
    • prevents cell from taking in too much water
    • made of teichoic acid  & lipoteichoic acid
      •  promote adhesion & anchor wall to membrane
    • Gram (-) = thin cell wall
      • little peptidoglycan + LPS + lipoprotein
    • Gram (+) = thick cell wall
      • lots peptidoglycan + teichoic acid
  • Outer Membrane - Gram (-) ONLY!
    • Gram (-) = biphospholipid membrane
      • inner leaf = ordinary phospholipids
      • outer leaf = lipopolysaccharides (LPS)
        • extremely toxic to humans (endotoxin)
  • Peptidoglycan layer - BOTH (+) and (-)
    • makes surface hydrophilic
      • Gram (+) = thick layer 
        • highly polar
      • Gram (-) = thin layer
        • less polar
  • Periplasm 
    • enzymes w/ hydrolytic functions; antibiotic-inactivating enzymes
      • Gram (-) = contains peptidoglycan
      • Gram (+) = small, no peptidoglycan
        • has proteins & oligosaccharides
  • Cell Membrane 
    • similar to familiar bi-leaflet membrane of most cells
      • made of phospholipids + proteins
    • ​Different than EUK b/c: 
      • NO STEROLS 
      • bacterial chromosome attached
      • site for DNA synthesis 
    • Functionally ~ mitochondria
    • Vital for growth & maintenance of cell

Appendages

  • Pili (Fimbriae) - protein
    • hair-like projections
      • found on both gram (+) and (-) species
      • specialize for adherence to certain cell types
    • made from pilin protein
      • tube w/ hollow core
    • 2 kinds: 
      • common 
        • adhesions = allow for colonization on surfaces
      • sex
        • allow for exchange of genetic material btw gram (-) bacteria
  • Flagella
    • rotating helical protein structures --> locomotion
      • rings on center rod
        • independent of ATP!
    • can be found: 
      • 1 singular pole (polar) 
      • tufts (lophotrichous) 
      • all over surface (peritrichous)
    • built from flagellin proteins
      • Antigenic = H Ags = targets for Ab response

Core

  • Cytosol - polyribosomes, proteins carbs, glycogen
    • granular b/c packed w/ lots of ribosomes
    • cytoskeleton elements 
  • Nucleoid - DNA & assoc RNA & protein
    • contains the genome 
    • single circular chromosome
    • nuclear bodies = 1 when resting; 4 is reproducing a lot
  • Plasmid - DNA
    • small, circular, covalently closed DNA 

3

What is the process & function of Gram-staining?

Gram staining: 

  • initially stained purple via crystal violet + iodine 
  • after decolorization + counterstain: 
    • gram (+) = keep stain --> purple
    • gram (-) = unstained --> red

Function

  • allows us to ID + treat for organism
    • Gram (+) = thick peptidoglycan layer
      • resists activity of bile in intestitine
      • digested by lysozymes 
      • disrupted by antibiotcs 
    • Gram (-) = thin peptidoglycan layer + outer membrane
      • (LPS) =
        1. toxic lipid A
        2. core polysaccharide 
        3. O Ag polysaccharide side chain = major surface Ag

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4

What are the differences in structure & function of Gram (+) & Gram (-) bacterial cell walls?

  1. Peptidoglycan
    • gram (+) = thick 
      • lots of peptidoglycan
    • gram (-) = thin
      • little peptidoglycan
  2. (lipo)teichoic acids
    • more in gram (-) 
  3. Porins
    • gram (-) 
  4. Lipopolysaccharide (LPS)
    • gram (-)
  5. Endotoxin
    • LPS = gram (-)

5

What happens to bacterial metabolism after glycolysis? 

Following glycolysis: 

  • 1 glucose --> 2 pyruvate (+ 2ATP)
    • if O2 present = aerobicrespiration --> lots of ATP
    • if no O2 = anaerobic fermentation --> no ATP

Aerobic Respiration

  • with O2, more energy can be made
  • pyruvate --> mitochondria --> 36 ATP (18x more energy) 
    • occurs in cell membrane

Anaerobic Fermenation

  • necessary if no O2 available (or if organism is resistant to O2)
  • cells cannot stockpile pyruvate
  • pyruvate --> lactic acid or other acids

Function in Bacteria & Role in Metabolism: 

  • O2 gives rise to at least 2 extremely reactive & toxic substances:
    • H2O2 
    • superoxide anion (O2-)
  • O2 --> O2- [superoxide dismutase] -->
  • H2O2 [catase] = H20 + O2 ....or
  • H2O2 [peroxidase] --> reduces NADH2 --> NAD = H20

Note: 

  • bacteria that LACK ability to make superoxide dismutase & catalase = grow anaerobically (sensitive to O2)

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6

What are the differences btw bacterial aerobes & anaerobes w/ respect to oxygen & mode of respiration?

​Basics: 

  • Bacteria response depends on:
    • ability to ferment or respire
    • ability to protect from deleterious effects of O2
      • aka do they have enzymes to break down oxygen

Leads to 4 General Classes:

  1. Aerobes
    • + O2 / + enzymes / - ferment
    • requires O2, cannot ferment
      • ex: fungi, protozoa, many bacteria (bacilis, TB)
  2. Anaerobes
    • - O2 / - enzymes / + ferment
    • killed by O2; ferments 
      • ex: oral/intestinal bacteria
  3. Facultative anaerobes
    • + O2 / + enzymes / + ferment
    • respires w/  O2, but can ferment if no O2 available
      • ex: gram (-) intestinal bacteria, staphylcoccci
  4. Microaerophiles
    • + O2 / + enzymes / + ferment
    • grows best at LOW O2
      • ex: bacteria that live in soil/water/host (h. pylori)

 

Note: 

Aerotolerant anaerobes

  • do not utilize O2, but can survive in its presence to a limited extent
  • NOT harmed by O2
    • have alternate mechanisms for breaking down H2O2 & superoxide
  • ex: lactobacilli & streptococci & clostridial species

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7

How does bacterial DNA replication occur?

Replication important for survival

Role of components: 

  • OriC
    • origin of replication
    • multienzyme replication complex (MeRC) binds to this & initiates unwinding & separation via
      • DNA gyrase (topoisomerase) = relaxes coiling
      • DNA helicase = removes H bonding & separates
  • DNA polymerase
    • replicates DNA via base pairs
    • Proof reading of new strand

Therapeutic targets:

  • quinoiones =
    • inhibit unwinding of DNA gyrase during replication 
  • penicillin = 
    • inhibitors of peptidoglyvcan cell wall synthesis

8

How does bacterial gene expression occur?

1. Transcription

  • DNA is copied by DNA-dependent RNA polymerase --> RNA transcript

Components: 

  • RNA polymerase
    • DNA --> mRNA
  • Promoter
    • nucleotide sequence in DNA that binds RNA polymerase
  • Operon
    • results in polycistronic arrangement 
    • provide a way of ensuring protein subunits of enzyme complexes are made in correct stoichiometry
  • Monocistronic
    • 1 promotor = 1 gene => 1 protein
  • Polycistronic
    • 1 promotor = signals many genes => many proteins

2. Translation:

  • exact sequence of AA of a protein = specificed by nucleotides in mRNA

Components

  • Initiation complex
    • starts mRNA --> protein via Shine-Dalgarno sequence where ribosomes bind
    • comprises of mRNA, ribosome, initiator tRNA + formyl methionine
  • Codon
    • tRNA reads and places AA
  • START & STOP codons
    • Start = AUG
    • Stop = UAA, UGA, UAG

Importance of bacterial coupling of these 2 processes: 

  • translation is started BEFORE transcription is COMPLETED
    • multiple ribosomes can bind to mRNA => polyribosome
    • bind to free 5' end of mRNA
  • protein synthesis = target of greater variety of antimicrobials than any other process

 

9

How are bacterial genes regulated? 

Purpose of gene regulation:

  • Bacteria adapt to environment by CONTROLLING gene expression

Important sites: 

  • Promoter (P) 
  • Operator site (O) 
  • Activation & activator
  • Repression & repressor 
  • Regulon
    • all genes controlled by SAME REGULATOR

Function of lac operon

  • (+) lactose & glucose
    • prefers metabolism of glucose
    • cAMP levels = low = CAP not activated
  • (+) lactose only 
    • cAMP levels rise = CAP activated = lac operon on 
  • (-) lactose & glucose
    • LacI binds to operator of lac promoter & BLOCKS transcription

Quorum sensing

  • specific gene transcription = activated in response to bacterial concentration
    • aka = biofilms (cystic fibrosis) 
  • at ceratin concentrations = activation of transcriptino of genes to turn on biofilm production

Environmental regulation of Gene Expression

  • 2 component regulation: 
    • signal transduction 
      • allows cellular function to react in response to changing environment
    • appropriate environmental stimulus results in AUTOPHOSPHORYLOATION of sensor proteins 
      • activates a response that affects gene regulation

 

 

10

What is the function of bacteral endospore formation? 

  • Endospore
    • small, dehydrated forms of bacteria
    • few species produce spores
      • anthrax, tetanus, botulism
    • GRAM (+) rods = medical relavent spores
  • Sporulation
    • 1 cell forms 1 spore under adverse conditions 
      • spore may persist for a LONGGG time ---> give rise to single vegetative bacterial cell
    • Process
      • walling off of nucleoid & surrounding cytosol
      • germination = activation by heat, acid, etc
        • initiation --> outgrowth of new vegetative cell that produced the spore

11

Describe & label bacterial growth cycle

4 Major phases: 

  • Lag phase
    • no growth
  • Exponential growth phase
    • LOTS of growth
  • Stationary phase
    • some cells start to die
    • no growth
  • Death phase
    • many cells die
    • some remain viable

Notes: 

  • Divide via binary fission
    • Happens in 20 minutes

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12

What are the 2 major bacterial mobile genetic elements?

  1. Plasmid
    • small, independently replicating extrachromosomal nucleic acid molecules
    • have genes for replication & transfer 
      • phenotypic advantages!
  • R plasmid
    • carry genes for resistance to antimicrobials
    • carry virulence genes & encode toxins
      • increase virulence of microorganism
  1. Transposable Elements
    • ​​DNA sequences that can jump (transpose) from a site in 1 DNA molecule to another in a cell
      • transposase gene
        • encodes enzyme necessary
      • IR & DRs
        • IR = inverted repeats
        • DR = direct repeats

​​​Notes: 

  • AKA= horizontal gene transfer

13

What are the major processes for bacterial genetic transfer?

  1. Transformation
    • involves release of DNA into environment by lysis
    • followed by uptake of that DNA from recipient cells
  2. Transduction
    • DNA is introduced into recipient cell by a bacteriophage (virus) 
      • lysogenic cycle = genome of virus = replicated passively as host cells replicate
      • lytic cycle = new virus particles are made & release when host cell lyses
        • virulent phages = limited to lytic cycle
  3. Conjugation (sex pilus)
    • involves actual contact btw donor & recipient cell 
    • plasmid is transfered

14

What are ways to classify bacteria?

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