LG5.5 bacterial cells Flashcards
Sketch a bacillus, coccus, vibrio, spirochete
What are the minimum requirements for a bacterial cell?
- DNA (in form of nucleoid) - loose DNA in cytoplasm
- plasma membrane (PM) (aka cytoplasmic membrane (CM) aka cell membrane)
- ribosomes
- cytoplasm
identify the layers of Gr+ bacterium
List some functions of the bacterial cell membrane) CM (aka plasma membrane (PM))
- phospholipid bilayer, proteins
- functional equivalent of most of the organelles of the eukaryotic cell!
- site of DNA synthesis
- site of cell wall polymer synthesis
- site of membrane lipid synthesis
- contains entire electron transport system
- passive, active transport
- secretion
Sketch the Gr+ cell envelope
What is teichoic acid? Is it found in Gr-, +, both?
Only found if Gr+. Glycerol and/or sugar with or without amino acids
Adds negative charge and staility.
Techoic acid that’s linked to CM is ‘lipotechoic acid’
Describe the petitoglycan layer in Gr+ bacteria.
- this layer also called ‘Murein’. Also called cell wall (CM)
- repeating NAM-NAG disaccharide cross-linked by amino acids
- THICK compared to Gr-
- negatively charged. provides stability, shape
Sketch crude Gr- envelope.
What is the outer membrane (OM)? Is it found on Gr+, -, both? What’s its function?
ONLY on Gr-
-relatively impermeable to large molecules and hydrophobic molecules like lysozymes, bile acids, detergents and some antibiotics
Describe lipidpolysaccharide (LPS). Is this component found in Gr-, Gr+, both?
- found ONLY in Gr- outer leaflet of OM
- strong negative charge
- O-antigen (aka O-polysaccharide): repeating chain of sugar units - this is the portion waving in the outside of the cell that the host immune system recognizes. this portion varies from species of bacteria
- lipid portion called lipid A (AKA endotoxin): toxic in high concentrations - causes septic shock (aka endotoxic shock aka gram negative shock). this portion is identical across most species
What are porin proteins? Are they in Gr+,- or both?
- Gr- ONLY.
- in the OM. allow passage of hydrophilic solutes.
What is the periplasmic space? Gr+,- or both?
- ONLY in Gr-
- between the CM and OM contains transport molecules and hydrolytic enzymes
Describe ‘gram staining’ procedure and results.
Give some defining characteristics of mycoplamsa bacteria.
- smallest of free-living prokaryotic cells
- normal flora in mouth, GI tract
- Lack cell wall (aka pleomorphic) - stains poorly
- sterols in PM
- resistant to penicillins and lysozymes
Give some defining characteristics of Chlamydia
- lacks peptidoglycan
- small Gr-
- obligate intracellular bacteria
- lacks machinery to synthesize ATP
Give some defining characteristics of Mycobacterium
- acid-fast rods
- gram stain does not work
- use Ziehl-Neelsen acid-fast stain (a differential stain) to stain
this differentiates acid fast bacteria from non-acid fast bacteria
- not called Gr - or Gr+
- molecular methods classify in Gr+
- have mycolic acids (fatty acids) external to cell wall - ‘waxy lipid coat
- hardy, relatively impenetrable, hydrophobic
- usually resistant to drying, many disinfectants
Provide the basic chemical composition, staining method (where covered) and function of bacterial capsules
- discrete layer, dense and well-defined
- certain Gr+, Gr-
- typically made of polysaccaride
- major role in pathogenic bacteria is protection from immune system (antiphagocytic)
E.g. Streptococcus pneumoniae
Gr+
recognize!
Outline the gram staining procedure for capsules.
bacteria negatively charged
↓
acidic dye’s (e.g. nigrosin, India ink, Congo red) negative ions repelled by negatively charged bacterial surface
↓
background stained
↓
stain cells w/ simple stain
Provide the basic chemical composition, staining method (where covered) and function of bacterial endospores.
- Bacterial Endospores
- Bacillus, Clostridium
- often soil-dwellers
- not reproductive, metabolically inactive, dormant
- sporulation (adverse growth conditions) hours; germination (favorable growth conditions) minutes
- not affected by boiling (>20 hrs), drying, acids, bases, radiation
- 121°C required to destroy
- dehydrated internally
- up to 20% dry weight endospore consists of calcium dipicolinate w/in core
Describe staining methods for endospores.
-refractile to stains
heat is required to drive a stain (e.g. malachite green) into endospores
↓
wash and counterstain w/ e.g. safranin
Provide the basic chemical composition, staining method (where covered) and function of flagella.
- motility, penetration→ requires energy
- movement toward or away from stimuli= taxis (E.g. chemotaxis)
- number and arrangement aids in classification
- ~15-20 nm diam.
- amino acid sequence varies from strain to strain…aids in classification
- detect motility in the lab with agar in test tube. puncture agar with bacteria-laden pick. Later, if agar is turbid (aka cloudy) then the bacteria are mobile and can spread out throughout agar. if agar clear, bacteria NOT mobile.
- spirochetes- Borrelia, Leptospira, Treponema
Provide the basic chemical composition, staining method (where covered) and function of pili
- attachment (adhesins)
- protein pilin subunits
- few to hundreds
- 3-8 nm diam.
- longer pilus= sex pilus
