Chapter 2 - Microbial Cell Structure and Function Flashcards Preview

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Flashcards in Chapter 2 - Microbial Cell Structure and Function Deck (251):
1

What kind of light does a compound light microscope use?

Visible light

2

How does a bright-field microscope work?

Specimens are visualized in contrast between specimen and surroundings

3

What are the lenses a bright-field microscope uses?

Objective and ocular lens

4

Magnification

The ability to make an object larger

5

Resolution

The ability to distinguish two adjacent objects as separate and distinct

6

Limit of resolution for a light microscope

0.2 μm

7

As wavelength decreases

Resolution improves

8

Two points are viewed as separate objects when

Light passes between them

9

What are dyes?

Organic compounds that bind to specific cellular materials

10

Simple Staining

One dye used to color specimen

11

Chromophore

Colored portion of dye

12

Basic dye

Positive charged chromophore
Binds to negatively charged molecule on cell surface

13

Acidic dye

Negatively charged chromophore
Repelled by cell surface
Used to stain background
Negative stain

14

Example of basic dye

Crystal violet

15

Example of acidic dye

Nigrosin

16

Gram positive

Cells that retain a primary stain - purple

17

Gram negative

Cells that lose the primary stain and take color of counterstain - red or pink

18

Acid fast stain

Detects mycolic acid in the cell wall of the genus Mycobacterium - pink, anything else will be blue

19

Endospore stain

Endospores retain primary - green, cells counterstained - pink

20

Phase-contrast microscopy

Phase ring amplifies differences in the refractive index of cell and surroundings

21

Advantages of phase-contrast microscopy

Improves the contrast of sample without the use of stain
Live samples can be seen

22

Phase-contrast appearance

Dark cells on a light background

23

Dark field microscopy

Specimen is illuminated with a hollow cone, only refracted light enters the objective

24

Dark field appearance

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