Chapter 2 - Microbial Cell Structure and Function Flashcards
1
Q
What kind of light does a compound light microscope use?
A
Visible light
2
Q
How does a bright-field microscope work?
A
Specimens are visualized in contrast between specimen and surroundings
3
Q
What are the lenses a bright-field microscope uses?
A
Objective and ocular lens
4
Q
Magnification
A
The ability to make an object larger
5
Q
Resolution
A
The ability to distinguish two adjacent objects as separate and distinct
6
Q
Limit of resolution for a light microscope
A
0.2 μm
7
Q
As wavelength decreases
A
Resolution improves
8
Q
Two points are viewed as separate objects when
A
Light passes between them
9
Q
What are dyes?
A
Organic compounds that bind to specific cellular materials
10
Q
Simple Staining
A
One dye used to color specimen
11
Q
Chromophore
A
Colored portion of dye
12
Q
Basic dye
A
Positive charged chromophore
Binds to negatively charged molecule on cell surface
13
Q
Acidic dye
A
Negatively charged chromophore
Repelled by cell surface
Used to stain background
Negative stain
14
Q
Example of basic dye
A
Crystal violet
15
Q
Example of acidic dye
A
Nigrosin
16
Q
Gram positive
A
Cells that retain a primary stain - purple
17
Q
Gram negative
A
Cells that lose the primary stain and take color of counterstain - red or pink
18
Q
Acid fast stain
A
Detects mycolic acid in the cell wall of the genus Mycobacterium - pink, anything else will be blue
19
Q
Endospore stain
A
Endospores retain primary - green, cells counterstained - pink
20
Q
Phase-contrast microscopy
A
Phase ring amplifies differences in the refractive index of cell and surroundings
21
Q
Advantages of phase-contrast microscopy
A
Improves the contrast of sample without the use of stain
Live samples can be seen
22
Q
Phase-contrast appearance
A
Dark cells on a light background
23
Q
Dark field microscopy
A
Specimen is illuminated with a hollow cone, only refracted light enters the objective
24
Q
Dark field appearance
A
Specimen is bright and background is dark
25
Advantages of dark field microscopy
Observe bacteria that don't stain well
26
Fluorescence microscopy
Used to visualize specimens that fluoresce
27
Fluorescence microscopy appearance
Emit light of one color when illuminated with another color of light. Some cells fluoresce naturally
28
Chlorophyll fluoresce
Absorbs light at 430 nm (blue-violet)
| Emits at 670 nm (red)
29
DAPI
Fluorescent dye that binds to DNA
30
Differential interference contrast microscopy
Uses a polarizer to create two distinct beams of polarized light
31
DIC microscopy appearance
Structures appear three-dimensional
32
DIC structures that can be seen
Endospores, vacuoles, and granules
33
Confocal scanning laser microscopy
Uses a computerized microscope coupled with a laser source to generate a three-dimensional image
34
Advantaged of CSLM
Can focus on a single layer
Layers can be compiled for a three-dimensional image
Resolution is 0.1 μm
35
Wavelength of electrons
Much shorter than light (better resolution)
36
Transmission electron microscope
Electron beam focused on specimen by condenser. Electrons pass through the specimen are focused by two sets of lenses. Electrons strike a fluorescent viewing screen.
37
What is used for a lens on a TEM?
Magnet
38
Advantages of TEM
High magnification and resolution (0.2 nm)
39
Specimen requirements for TEM
Must be very thin (20-60 nm)
| Must be stained with metal - lead or uranium
40
Why must a cell be stained with a metal?
To make them more electron dense
| Enables visualization of structures at molecular level
41
Scanning electron microscopy
Specimen is coated with a thin film of heavy metal (e.g., gold). An electron beam scans the object. Scattered electrons are collected by a detector and an image is produced.
42
SEM image
3D image of a specimen's surface
43
Bacteria
Diverse metabolism
Live in a broad range of ecosystems
Pathogens and non-pathogens
44
Archaea
Diverse metabolism
Live in extreme environments
Non-pathogens
45
Coccus
Roughly spherical
46
Bacillus
Rod shaped
47
Spirillum
Spiral shaped
48
Spirochete
Spiraled and more flexible
49
Budding and appendaged bacteria
Have a stalk or hyphae
50
Filamentous bacteria
Appear like hyphae
51
Morphology does not predict
Physiology, ecology, phylogency
52
What shape of cells promote gliding motility?
Filamentous
53
What shape of cell allows swimming motility?
Helical or spiral-shaped
54
Advantages of small cells or those with high surface-to-volume ratio
Optimization for nutrient intake
55
Size range for prokaryote cells
0.2 μm to >700 μm
56
Size range for eukaryote cells
10 μm to >200 μm
57
Advantages of small cells
Higher surface area relative to cell volume
Support greater nutrient exchange per unit cell volume
Tend to grow faster
58
Lower limits of cell size
59
Small cells are found in
Open oceans
60
Cytoplasmic membrane
Thin structure that surround the cell, it separates the cytoplasm from the environment
Highly selective permeable barrier
Enables concentration of specific metabolites and excretion of waste products
61
General structure of membranes
Phospholipid bilayer
62
Phospholipid bilayer
Hydrophobic (fatty acids) and hydrophobic (glycerol-phosphate) components
63
Location of fatty acids and hydrophilic portions
Fatty acids point inward to form hydrophobic environment; hydrophilic portion remains exposed to external environment
64
Ester phospholipids
Glycerol, 2 fatty acids, phosphate, and optional side chain
65
Amphipathic
Has both polar and non-polar characteristics
66
Polar
Molecule carries a charge
| Hydrophilic
67
Non-polar
Molecule is uncharged
| Hydrophobic
68
Gram negative membrane proteins
Interacts with a variety of proteins (periplasmic proteins) that bind substrates or process large molecules for transport
69
Inner surface of cytoplasmic membrane
Interacts with proteins involved in energy-yielding reactions and other cellular functions
70
Integral membrane proteins
Firmly embedded in the membrane
71
Peripheral membrane proteins
One portion anchored in the membrane
72
Archaeal membrane linkages
Ether linkages in phospholipids
73
Bacterial and Eukarya membrane linkages
Ester linkages
74
Archaeal lipids lack and have what instead
Fatty acids; have isoprenes
75
Archaeal major lipids
Glycerol diethers and triethers
76
Structure of archaeal lipid
Monolayers, bilayers, or mixture
77
Advantage of monolayer lipid
Extremely heat resistant
78
Where are monolayer lipids usually found?
Hyperthermophilic archaea
79
Permeability barrier
Polar and charged molecules must be transported
| Transport proteins accumulate solutes against the concentration gradient
80
Protein anchor
Holds transport proteins in place
81
Energy conservation
Site of generation of proton motive force
82
Carrier-mediated transport systems
Show saturation effect
| Highly specific
83
Three major classes of transport systems in prokaryotes
Simple transport
Group translocation
ABC system
84
Simple transport
Driven by the energy in the proton motive force
85
Group translocation
Chemical modification of the transported substance driven by PEP (phosphoenolpyruvate)
86
What does all transport systems require?
Energy in some form, usually proton motive force or ATP
87
ABC system
Chaperone protein is used to lead the protein to the port (periplasmic binding)
88
Three transport events
Uniport, symport, antiport
89
Uniport
One direction across the membrane
90
Symport
Co-transporters (two molecules moves across membrane in same direction)
91
Antiporters
One molecule into the membrane, one molecule out
92
Example of simple transport
Lac permease of E. coli
93
Lac permease
Helps transport lactose and H+ into E. coli
94
Group translocation
Sugar is phosphorylated during transport across the membrane
Moves glucose, fructose, mannose
Phosphoenolpyruvate (PEP) donates a P to a phosphorelay system
P is transferred through a series of carrier proteins and deposited onto the sugar as it is brought into the cell
95
ABC transport systems
Involved in uptake of organic compounds (sugars, amino acids), inorganic nutrients (sulfate, phosphate), and trace metals
96
ABC transport systems display
High substrate specificity
97
ABC transport systems (gram-negative)
Employ periplasmic-binding proteins and ATP-driven transport proteins
98
ABC transport systems (gram positive)
Employ substrate-binding lipoproteins (anchored to external surface of cell membrane) and ATP driven transport proteins
99
ABC transports
Solute binding proteins, integral membrane proteins, ATP-hydrolyzing proteins
100
Solute binding protein
Periplasm
| Binds specific substrate
101
ATP-hydrolyzing proteins
Supply energy for the transport event
102
Cell walls of bacteria and archaea
Rigid - help maintain cell shape
Porous to most small molecules
Protects cell against osmotic changes
103
Role of cell wall
Prevent cell expansion - protects against osmotic lysis
Protects against toxic substances - large hydrophobic molecules (detergents, antibiotics)
Pathogenicity
Partly responsible for cell shape
104
Pathogenicity
Helps evade host immune system
| Helps bacterium stick to surfaces
105
Gram-negative cell wall
Two layer: LPS (lipopolysaccharide) and peptidoglycan
106
Gram-positive cell wall
One layer: peptidoglycan
107
Peptidoglycan
Rigid layer that provides strength to cell wall
108
Polysaccharide composed of
N-acetylglucosamine and N-acetylmuramic acid (NAG and NAM sugars)
Amino acids
Lysine or DAP
109
Polysaccharide form
Glycan tetrapeptide
110
Number of peptidoglycan structures identified
More than 100
111
How do peptidoglycan differ?
In peptide cross-links and/or interbridge
112
Where are interbridges found?
In gram-positive bacteria, none in gram-negative
113
How many interbridges does S. aureus have?
5 glycine residues
114
How much peptidoglycan do gram-positive cell walls have?
Up to 90%
115
What do gram positive bacteria have in their cell wall?
Teichoic acid
116
Lipoteichoic acid
Teichoic acids covalently bound to membrane lipids
117
Backbone of peptidoglycan
NAM and NAG connected by glycosidic bonds
118
Glycoside bonds
Crosslinks formed by peptides
119
Shape of peptidoglycan strand
Helical
120
Why is the peptidoglycan strand helical?
Allows 3-dimensional crosslinking?
121
How many layers of peptidoglycan does E. coli have?
1
122
How many layers of cell walls does Bacillus species have?
50-100
123
Prokaryotes that lack cell walls
Mycoplasmas
| Thermoplasmas
124
Mycoplasmas
Group of pathogenic bacteria
| Have sterols in cytoplasmic membrane - adds strength and rigidity to membrane
125
Thermoplasma
Species of archaea
| Contain lipoglycans in membrane that have strengthening effect
126
How much peptidoglycan do gram negative bacteria have?
10%
127
What does the lipopolysaccharide layer consist of?
Core polysaccharide and O-polysaccharide
128
What does LPS replace?
Most of phospholipids in outer half of outer membrane
129
Endotoxin
Toxic component of LPS
130
Periplasm
Space located between cytoplasmic and out membrane
131
Size of periplasm
~15 nm wide
132
Consistency of periplasm
Gel-like
133
What does the periplasm contain?
Proteins
134
Porins
Channels for movement of hydrophilic low-molecular weight substances
135
Gram-positive bacteria cell walls
Thick consisting mainly of peptidoglycan
136
What happens to gram-positive bacteria cell walls during alcohol step of staining?
Pores in wall close and prevent crystal violet from escaping
137
What happens to gram-negative bacteria cells wall during alcohol step of staining?
Alcohol penetrates outer membrane, crystal violet is extracted out, and cells appear invisible until counterstained with second dye
138
Archael cell walls
No peptidoglycan and typically no outer membrane
139
Pseudomurein
Polysaccharide similar to peptidoglycan
140
What is pseudomurein composed of
NAG and N-acetylalosaminuronic acid (NO NAM)
141
Where is pseudomurein found?
Certain methanogenic archaea
142
S-layers
Most common cell wall type among archaea
143
S-layers consist of
Protein or glycoprotein
144
S-layer structure
Paracrystalline structure
145
True/false: some archaea only have S-layer (no other cell wall components)
True but most have additional cell wall elements
146
Cell wall structure function in archaea
Prevent osmotic lysis and give shape
147
Lack of peptidoglycan means archaea are resistant to
Lysozome and penicillin
148
Cytoplasm
Material bounded by plasma membrane
149
Protoplast
PM and everything within:
| Macromolecules, soluble proteins, DNA and RNA, ribosomes, inclusions
150
Enzymes
Catalyze chemical reactions
151
Transport proteins
Move other molecules across membranes
152
Structural proteins
Help determine shape of cell and are involved in cell division
153
Proteins are made of
Polypeptides
154
Polypeptides
A long polymer of amino acids joined by peptide bonds
155
Nucleoid
Region that contains the genome
156
Typical bacterial genome
Single circular double stranded DNA chromosome and may have one or more plasmids
157
Plasmid
Small circular double stranded DNA that is self-replicating and carry non-essential genes
158
DNA
Carries genetic info of all living cells
| Polymer of deoxyribonucleotides
159
Bacterial ribosomes
Site of protein synthesis
160
What are the parts of the 70S ribosome?
30S subunit - 16S rRNA
| 50S subunit - 23S and 5S rRNA
161
Cytoplasmic ribosomes
Cytoplasmic proteins
162
PM associated ribosomes
Membrane proteins
| Proteins to be exported from the cell
163
Capsules and slime layers
Polysaccharide/protein layers that assist in attachment to surfaces
164
Capsule and slime layer appearance
Thin or thick, rigid or flexible
165
Benefits of capsule and slime layer
Protect against phagocytosis and resist desiccation
166
Fimbriae
Filamentous protein structure that enable organisms to stick to surfaces or form pellicles
167
Pili
Filamentous protein structure that assist in surface attachment
168
Which is longer fimbriae or pilli
Pili
169
What does the pili facilitate?
Genetic exchange between cells (conjugation)
170
What type of pili are involved in twitching motility?
Type IV
171
Cell inclusion bodies
Visible aggregates in cytoplasm
172
Types of cell inclusion bodies
Carbon storage polymers: poly-beta-hydroxybutyric acid, glycogen
Polyphosphates
Sulfur globules
Magnetosomes
173
What are carbon storage polymers?
poly-beta-hydroxybutyric acid (lipid) and glycogen (glucose polymer)
174
Polyphosphates
Accumulations of inorganic phosphate
175
Sulfur globules
Composed of elemental sulfur
176
Magnetoaomes
Magnetic storage inclusions
177
Inorganic inclusions
Polyphosphate granules and sulfur golbules
178
Polyphosphate granules
Volutin - storage of phosphate and energy
179
Sulfur globules
Storage of sulfur used in energy generation
180
Magnetosomes
Intracellular granules of Fe3O4 or Fe3S4
181
Magnetosomes ability
Gives the cell magnetic properties that allow it to orient itself in a magnetic field
182
Magnetotaxis
Bacteria migrate along Earth's magnetic field
183
Gas vesicles
Confer buoyancy in planktonic cells
184
Gas vesicle appearance
Spindle-shaped, gas-filled structures made of proteins
185
Gas vesicle function
Decreasing cell density
186
Endospores
Highly differentiated cells resistant to heat, harsh chemicals, and radiation
187
What stage are endospores for a bacterial life cycle?
Dormant
188
How do endospores travel?
Wind, water, or animal gut
189
Bacterial endospores are only produced by
Gram positives
190
Vegetative cell
Capable of normal growth - metabolically active
191
Endospore
Dormant cell, formed inside of a mother cell
192
Endospore: metabolically active or inactive
Inactive
193
How are endospores triggered?
By lack of nutrients
194
How long does it take for an endospore to form?
8-10 hours
195
Layers of endospore
Spore coat and cortex and two membranes
196
Spore coat and cortex
Protect against chemicals, enzymes, physical damage, and heat
197
Two membranes of endospores
Permeability barriers against chemicals
198
Endospore core
Dehydrated - protects against heat
199
Endospore core is made of
Ca-dipicolinic acid and SASPs that protect against DNA damage
200
Endospores can resist
```
Boiling for hours
UV, gamme radiation
Chemical disinfectants
Dessication
AGe
```
201
First stage of spore forming bacterium
Assymetric cell division - DNA replicates and identical chromosomes are pulled to opposites end of the cell
202
Second stage of spore forming bacterium
Septation - divides into 2 unequal compartments: the forespore and mother cell
203
Third stage of spore forming bacterium
Mother cell engulfs the forespore - the forespore is now surrounded by two membranes
204
Fourth stage of spore forming bacterium
Formation of cortex - thick layers of peptidoglycan form between the two membranes
- highly cross-linked layer - core wall
- loosely cross-linked layer - cortex
205
Fifth stage of spore forming bacterium
Coat synthesis - protein layers surround the core wall (spore coat and exosporium) to help protect the spore from chemicals and enzymes
206
Sixth stage of spore forming bacterium
Endospore matures
- core is dehydrated
~ 10-30% of vegetative cell's water content
207
Seventh stage of spore forming bacterium
Mother cell is lysed
- mother cell disintegrates
- mature spore is released
208
Flagella
Hollow protein filaments
209
Flagella can be viewed
Only when stained
210
Monotrichous
Single flagellum - polar or subpolar
211
Amphitrichous
Flagella at opposite ends
212
Lophotrichous
Multiple flagella in a single tuft
213
Peritrichous
Flagella distributed around cell
214
Flagella structure
Filament, hook, and basal body
215
Flagella filament
Rigid helical protein - 20 micrometers long
| Composed of identical protein subunits - flagellin
216
Flagella hook
Flexible coupling between filament and basal body
217
Basal body
Consist of central rod that passes through series of rings
218
Basal body rings
L ring - LPS layer
P ring - peptidoglycan
MS ring - membrane
C ring - cytoplasm
219
Where does the energy comes from to turn the flagella?
Proton motive force
220
Proton motive force
Gradient of protons across the cytoplasmic membrane
- high [H+] outside
- low [H+} inside
221
Mot proteins
Form a channel that allows H+ to move into the cytoplasm
| Provides the energy to turn the flagellum
222
How does the flagellum turn?
Like a propeller to drive the cell forward
223
Flagellar synthesis
MS ring is made first, other proteins and hook are made next, filament grows from tip
224
Peritrichously flagellated cell movement
Slowly in a straight line
225
Polarly flagellated cell movement
Rapidly and typically spin around
226
Gliding motility
Flagella-independent motility that is slower and smoother than swimming
227
Gliding motility requires
Surface contact
228
Mechanisms of gliding motility
Excretion of polysaccharide slim
Type IV pili
Gliding-specific proteins
229
Taxis
Directed movement in response to chemical or physical gradients
230
Chemotaxis
Response to chemicals
231
Phototaxis
Response to light
232
Aerotaxis
Response to oxygen
233
Osmotaxis
Response to ionic strength
234
Hydrotaxis
Response to water
235
Chemotaxis is best studied in
E. coli
236
Chemotaxis response
To temporal not spatial differences in chemical concentration
237
Chemotaxis behaviour
Run and tumble behaviour
238
Chemoreceptors
Used to sense attractants and repellants - biased random walk
239
What happens if E. coli senses that glucose is increasing?
Tumble is delayed and the run lasts longer
240
Chemotaxis is measured by
Inserting a capillary tube containing an attractant or a repellent in a medium motile bacteria
It can be seen under a microscope
241
Eukaryotic cell size
Lower surface area to volume ratio
- Need more sophisticated transport mechanisms
- Grow slower
242
Eukaryote nucleus
True nucleus that houses the genetic material
243
Eukaryote internal structures
Membrane bound organelles
Intracytoplasmic membranes used for transport
Cytoskeleton
244
Nucleus DNA
Multiple linear dsDNA chromosomes
245
Chloroplasts
Site of photosynthesis for chlorophyll
246
How many membranes is the chloroplast surrounded by?
2 membranes
247
Mitochondria
Site of respiration and oxidative phosphorylation
248
Endosymbiotic hypothesis
Mitochondria and chloroplasts evolved from bacteria
249
What is the evidence for the endosymbiotic hypothesis?
```
Semi-autonomous
Circular chromosomes - lack histones
70S ribosomes
Two membranes
Outer membrane has porins
```
250
Mitochondria are most related to
Rickettsia - proteobacteria (obligate intracellular pathogens)
251
Chloroplasts are most closely related to
Cyanobacteria - blue-green algae
