Lecture 3: Bacterial Cell Structure Flashcards
(105 cards)
1
Q
Cocci Shape Arrangement and the 5 types
A
Spherical cells (Diplococci, Streptococci, Staphylococci, Tetrads, and Sarcina)
2
Q
Diplococci
A
Divide on 1 plane and create pairs
3
Q
Streptococci
A
Divide in 1 plane and create chains
4
Q
Staphylococci
A
Divide in random or 3 planes and create grape-like clusters
5
Q
Sarcina
A
Divide in 3 planes and create cubic packet of 8 cocci
6
Q
Tetrads
A
Divide in 2 planes and make a square of 4 cocci
7
Q
Bacilli Shape Arrangement and Coccobacili
A
rods where length to width ratio differs and coccobacili are short and wide rods.
8
Q
Vibrios
A
Comma-shaped
9
Q
Spirilla
A
Rigid spiral-shaped
10
Q
Spirochetes
A
flexible spiral-shaped
11
Q
Mycelium
A
network of long filaments (hyphae)
12
Q
Pleomorphic
A
organisms that are variable in shape
13
Q
Bacterial cell sizes (small, average, very large)
A
Small: 0.3 micrometers
Average: 1.1-1.5 micrometers wide by 2-6 micrometers long
very large: 600 by 800 micrometers
14
Q
Cells want a ___ surface area to volume ratio and why
A
high; increases efficiency of nutrient uptake and diffusion of molecules within a cell.
15
Q
radius is __ for surface area and __ for volume meaning that volume __
A
Squared; cubed | volume increases at a greater ratio than surface area
16
Q
Bacterial cell envelope is made up of __ and their order
A
plasma membrane (innermost), cell wall (middle), and glycocalyx (capsule or slime layer) outermost
17
Q
Plasma membrane functions
A
- Acquires nutrients
- Eliminates waste
interacts with external environment by
-detecting/responding to surrounding chemicals
-transport systems used for nutrient uptake
-metabolic processes (respiration and photosynthesis)
18
Q
Plasma membrane structure
A
- Thin (7 to 8 mm) made of 2 lipid sheets.
- floating and flexible
- proteins can shift around inside of them
- tails made of glycerol backbone and fatty acid chains.
19
Q
Lipids in plasma membrane
A
hopanoids: hydrophobic molecules that act as cholestrol does in eukrayotes making membrane more flexible.
20
Q
Hopanoids
A
- distort bilayer and impact fluidity and membrane shape.
- form functional membrane micro-domains that are platforms for protein complex assembly.
21
Q
Two types of membrane proteins in plasma membrane
A
Peripheral: loosely connected to membrane/ easily removed (20-30% of total membrane proteins).
Integral: amphipathic (hydrophilic and hydrophobic) embedded within membrane/not easily removed.
- play important role in transportation across membrane.
22
Q
Macronutrients
A
- required in large amounts and from food.
- found in organic molecules (proteins, lipids, nucleic acids, and carbs).
- important for protein synthesis.
-cations contribute to activity and stability of molecules and cell structures.
-important in cellular processes and chemical reactions.
23
Q
Micronutrients
A
-required in small amounts
- found everywhere in nature for microbial growth.
- assist enzyme catalysis
- maintain protein structure
24
Q
Growth factors
A
- organic compounds required for survival
- essential cell components
- cell cannot synthesize and is needed from environment
25
The transport mechanisms microorganisms use:
* Passive diffusion
* Facilitated diffusion
* Primary and secondary active transport
* Group translocation
26
Passive diffusion
* Molecules move from higher to lower concentration.
* requires large concentration gradient for good nutrient uptake (greater cg greater diffusion)
* rate of diffusion decreases as more nutrients accumulate in cell.
* water, oxygen, and carbon dioxide use this.
27
Facilitated diffusion
* movement across membrane w/ help of transport proteins.
* channels: form pores for substance to pass through.
* carriers: have high substrate specificity and physically attach to substance, protein change shape/folds.
* rate increases with concentration gradient.
28
Rate of facilitated diffusion is__
higher than passive diffusion but it reaches a plateau because all proteins are saturated aka bound up.
29
Active transport
* transport of molecules against concentration gradient.
* energy-dependent: ATP or proton motive force is used.
* involved carrier proteins that control transport rate.
* when solute concentration is high, carrier saturation effect is observed.
30
Active transport
* transport of molecules against concentration gradient.
* energy-dependent: ATP or proton motive force is used.
* involved carrier proteins that control transport rate.
* when solute concentration is high, carrier saturation effect is observed.
31
Primary active transport
* Use energy from ATP hydrolysis to move substances against concentration gradient without modifying them.
* Certain binding proteins help move molecule into pore.
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Uniporters
- single molecule transported across.
- only in primary active transport
- ATP-binding cassette (ABC) transporters
33
ATP-binding cassette (ABC) transporters
consist of
- 2 hydrophobic membrane spanning domains.
- 2 cytoplasmic associated ATP-binding domains.
34
Secondary active transport
- use potential energy of ion gradients to cotransport substances without modifying them.
- move both ion and substance across the membrane.
- There's second pump creating gradient; doing it through the potential energy of another molecule.
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Symporter
- 2 substances both move in the same direction.
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Antiporter
- 2 substances move in opposite directions.
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Group translocation
- Energy dependent and chemically modifies molecule.
- Imports sugars while phosphorylating them.
- add phosphate group to molecule.
- best known translocation system is PTS.
38
Iron Uptake why is it needed?
microorganims require iron for
- building molecules important in energy-conserving processes.
- ferric iron is very insoluble so uptake is difficult.
- siderophores are needed
39
Siderophores
- Secreted by bacteria to get ferric ion to transport into cell.
They chelate iron by taking it from host and forming complex with it.
40
Bacterial cell wall functions
- maintains bacterium shape.
- protects cell from osmotic pressure/lysis & toxins.
- contributes to pathogenicity.
41
peptidoglycan and shape
It's a murein rigid structure lying outside plasma membrane and has a helical shape.
- mesh-like polymer of identical subunits of long strands.
- Made of interchanging molecules between NAG and NAM.
- combination of peptides and a sugar molecule.
42
Two types of bacteria abased on gram stain
gram positive and gram negative bacteria
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Peptidoglycan chains are __
cross-linked by peptides for strengths.
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Direct crosslink
connecting carboxyl group and amino groups between amino acids.
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Indirect crosslink
peptide interbridge may form
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Gram-positive cell wall
Stain purple and have thick peptidoglycan.
Monoderm - single membrane.
Contain teichoic acids (negatively charged)
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Teichoic acids
- polymers of glycerol.
- help maintain cell envelope.
- protect from environmental substances.
- may bind to host cell to initiate infection.
48
Periplasmic space of gram-positive bacteria:
- Between plasma membrane and cell wall.
- Periplasm has relatively few proteins.
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Gram-negative cell wall
- Thin peptidoglycan layer surrounded by outer membrane.
- stain pink or red
- diderm: plasma membrane and an outer membrane
50
Outer membrane of gram-negative cell wall
Composed of lipids, lipoproteins, and lipopolysaccharides (no teichoic acids).
- have long thread-like molecules coming off of them called lipopolysaccharides.
- important for attachment with host cell.
- If polysaccharides caught up in circulation, you can get septic shock.
51
Lipopolysaccharide (LPS) structure:
1. Lipid A: buried in outer membrane.
2. Core polysaccharide: 10 sugar structure joined with lipid A.
2. O side chain (O antigen): polysaccharide that extends outward from core and binds to other cells.
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LPS importance
- contributes negative charge on cell surface
- stabilizes outer membrane structure
-creates a permeability barrier
- host defense potection
- acts as an endotoxin
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Periplasmic space
- may constitute 20-40% of cell volume.
- many enzymes present: hydrolytic enzymes, transport proteins, and other proteins.
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Gram-negative membrane transport steps
1. solute crosses outer membrane into periplasm.
2. solute then crosses the plasma membrane.
Facilitated transport by porins: if molecule is right shape/size it can fit and pass.
- Allows channels to let small molecules pass (600 daltons).
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Hypotonic environments
Solute concentration outside is less than inside cell.
-water moves into cell and cell swells.
- cell wall protects from lysis.
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Hypertonic environments
Solute concentration outside is greater than inside.
- water leaves cell and cytoplasm shrivels up.
- plasmolysis.
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Glycocalyx
- polysaccharide extension that aids in attachment to solid surfaces.
- it is outermost layer of cell envelope.
- can be capsule or slime layer.
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Capsules
- polysaccharides covalently bonded & harder to wash away.
- visible in light microscope and well organized.
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Capsules functions
Resistant to phagocytosis.
Helps with bacterial survival.
Protect from desiccation (cells drying out).
Exclude viruses and detergents.
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Slime and functions
- unorganized polysaccharides.
- easily wash away and diffuse.
- gliding bacteria make it to facilitate motility.
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S-layers and functions
Structured self-assembling layers of proteins/glycoproteins.
FUNCTIONS:
- maintain shape and rigidity.
- promote adhesion to surfaces.
- protects from host defenses.
- potential use in nanotechnology.
- protect from ion and ph fluctuations, osmotic stress, enzymes, and predation.
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S-layers in gram positive bacteria
Associated with peptidoglycan.
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S-layers in gram negative bacteria
Adheres to outer membrane
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Bacterial cytoplasmic structures
Cytoskeleton
Intra-cytoplasmic membranes
Inclusions
Ribosomes
Nucleoid
Plasmids
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Bacterial Cytoskeleton
Protein filaments that polymerize and extend to full inner dimensions of the cell.
Homologs of eukaryotic cytoskeletal elements have been identified in bacteria.
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Cytoskeleton functions
* Participate in cell division.
* Localize proteins.
* Maintain cell shape.
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Three types of cytoskeleton protein filaments:
FtsZ: forms Z ring at center of dividing cell that becomes. narrower as daughter separates.
MreB: maintains shape by positioning peptidoglycan synthesis machinery (many rods).
CreS: maintains curve shape
68
Intracytoplasmic membranes
Plasma membrane infoldings seen inside cell.
May be aggregates of vesicles.
Observed in photosynthetic bacteria.
Observed in bacteria with high respiratory activity.
69
Inclusions (inside cells)
Formed by aggregation of organic/inorganic substances.
Aren’t organelles; not bound by membranes but compartments for specific functions.
70
Primary function of inclusions (inside cells)
- segregate cellular components so they don't diffuse freely in the cytoplasm.
- Granules, crystals, or globu;es of organic or inorganic material are stockpiled by cell for future use.
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Micro-compartments
Inclusions enclosed by a single-layered protein shell that sequester enzymes that produce toxic intermediates.
72
Carboxysomes (inclusions)
Site of CO2 fixation in CO2 fixing bacteria.
- fixing is ability to convert and breakdown nitrogen or CO2 to make cellular components.
- contain enzyme carbonic anhydrase that releases CO2 into a shell so it accumulates to higher concentration then RuBisCO catalyzes CO2 into sugar.
73
Gas vacuoles (inclusions)
- made of aggregates of hollow, cylindrical gas vesicles.
- use photosynthesis to change their depth based on how much light is coming.
- Changing gas inside these vacuoles can change their buoyancy levels and float or sink.
74
Gas vacuoles functions
* Involved in movement, provide buoyancy to aquatic bacteria.
* Control exposure to light for photosynthesis.
75
magnetosomes (inclusions)
Made of magnetite particles for orientation in Earth’s magnetic field (found in aquatic bacteria).
* Cytoskeletal protein MamK helps form magnetosome chain.
76
Magnetosomes functions
* Provides direction to nutrient-rich sediments or depth in water.
77
Ribosomes
- Sites of protein synthesis.
- complex protein/RNA structures made of subunits.
- bacterial and archaeal ribosomes = 70S
Bacterial ribosomal RNA:
- 16S rRNA in small subunit.
- 23S and 5S rRNA in large subunit.
78
Nucleoid
- Where genetic material resides.
- location of chromosome and associated proteins.
79
DNA in nucleioid
- Usually 1 closed circular double-stranded DNA.
- Supercoiling/nucleoid proteins aid in folding.
- DNA molecule itself continues to loop to be compacted and fit in the cell.
80
Plasmids
Extrachromosomal DNA that's small closed circular DNA molecules.
- inherited during cell division.
- exist and replicate independently of chromosomes.
81
Episomes
Plasmids able to integrate into chromosome.
- carry genes that can confer a selective advantage in some situations (antibiotic resistance genes).
82
External structures in bacteria and function
Extend beyond cell envelope.
- function in protection, attachment to surfaces, horizontal gene transfer, cell movement.
- Pili and fimbriae - Flagella
83
Pili and fimbriae and function
shot thin hairlike protein appendages (1000/cell)
- can mediate attachment to surfaces, motility, and DNA uptake.
- when bacteria attach to surface they can take nutrients.
84
Sex pili
- Longer, thicker, less numerous (10/cell)
- Genetically encoded on plasmids.
- Required for conjugation: to bacterial cells coming together from a sex pili.
85
Flagella
threadlike, locomotor protein structures extending outward from plasma membrane and cell wall.
- can't be observed with bright-field microscope unless specially stained.
86
Flagella functions
- helps with motility
- attachment to surfaces
- virulence factors - contribute to ability to cause disease.
87
patterns of flagella distribution:
Monotrichous, amphitrichous, lophotrichous, and petritrichous.
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Monotrichous
One flagellum
- Polar flagellum: flagellum at end of cell.
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Amphitrichous
one flagellum at each end of cell.
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Lophotrichous
cluster of flagella at one or both ends.
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peritrichous
spread over entire cell surface.
92
Structure of bacterial flagella
- filament: extends from cell surface to the tip.
- hook: short curved segment.
- basal body: embedded in cell envelope.
Actual filament is the long line we see which enters the cell using the hook that enters the basal body.
93
Flagellar movement and motility
* Swimming, swarming, spirochete motility
* Twitching and gliding motility * Chemotaxis
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Flagellar Swimming
- flagellum moves/rotates in propelling circular motion.
-very rapid up to 1100 revolutions/sec.
- Conterclockwise: forward motion run
- Clockwise: disrupts run causing cell to stop and tumble
95
flagellar Swarming
- occurs when cells move in unison across moist surfaces.
- most swarmers have peritrichous flagella.
- cell produces molecule that lower surface tension (surfactants)
96
Flagellar Spirochete Motility
- Undulation of entire cell (moves up and down)
- Multiple flagella form axial fibril (winds around cell)
- flagella remains inside cell wall.
- corkscrew shape exhibits flexing and spinning movements.
97
Chemotaxis
- movement towards chemical attractant or away from a chemical repellent.
* In presence of attractant/repellent, tumbling frequency is reduced; runs toward/away from compound are longer.
* Behavior of bacterium altered by temporal concentration of chemical.
98
Chemotaxis process
- Chemical attractants/repellents bind chemoreceptors that transmit signals throughout chemosensing system.
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Chemotaxis process
- Chemical attractants/repellents bind chemoreceptors that transmit signals throughout chemosensing system.
100
Bacterial endospore
Complex, dormant structure formed by some bacteria inside of a parent cell.
- forms in response to nutrient depletion.
* Spores form when nutrient levels are low or conditions for growth are no longer so favorable.
- Resistant to numerous environmental conditions: Heat, UV radiation, gamma radiation, chemical disinfectants, and desiccation.
- Some are dangerous eg. Clostridium botulinum.
Paralyzes muscles and causes food poisoning.
101
Endospore structure
Exosporium: spore surrounded by thin covering.
Coat: under exosporium, thick layer of protein.
Cortex: between outer membrane and cell wall.
- beneath coat, thick peptidoglycan.
Core: under inner membrane has nucleoid and ribosomes.
102
Sporulation
* Process by which endospores form (over hours).
* It needs a mother cell to house it (sporangium).
103
Endospore formation
cell division
1. axial filament formation: filaments start to form on one side.
2. septum formation: two different structures within same cell.
3. forespore engulfment: forespore forms
4. cortex formation: more development in different layers.
5. coat synthesis: coat formation & extra layer of peptidoglycan.
6. endospore maturation
7. sporangium lysis: mother cell dies off and releases spore.
104
vegetative cell
A cell of a bacteria that is actively growing rather than forming spores.
105
Three stages of vegetative cell formation
1. Activation: prepares endospores for germination
3. Germination: starts when germinant receptors detect small molecules (sugars and amino acids)
4. Outgrowth: emergence of vegetative cells,
