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Exam 1: Bacterial Cell Structures Flashcards

1
Q

What are the 2 classes of cell envelope?

A

Gram-positive and gram-negative

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2
Q

What is the classification of the cell envelope based on?

A

The ability of a species to retain a crystal violet-iodine stain when treated with organic solvents

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3
Q

What does the staining property of the cell envelope depend on?

A

The morphology and composition of the bacterial envelope

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4
Q

What is the gram-positive envelope structure?

A

Cell membrane: phospholipid bilayer similar to eukaryotic membranes
Cell wall: located outside cell membrane. Thick peptidoglycan layer

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5
Q

What is the gram-negative envelope structure?

A

Inner membrane: phospholipid bilayer similar to gram-positive cell membrane and eukaryotic membranes
Cell wall: peptidoglycan layer that is much thinner that gram-positive cell wall
Outer membrane: inner leaflet is phospholipid, but outer leaflet is a unique bacterial structure- lipopolysaccharide

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6
Q

Look at photo with differences between gram negative and gram positive

A

Look at photo with differences between gram negative and gram positive

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7
Q

What occurs due to gram-positive bacteria having a thicker cell wall?

A

They have an increased resistance to mechanical, heat or drying damage

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8
Q

What occurs due to gram-negative bacteria having the presence of the outer membrane?

A

The envelope is more impermeable, especially to hydrophilic compounds

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9
Q

What does the more impermeable membrane of gram-negative do?

A

Makes the bacteria less susceptible to many toxic compounds

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10
Q

What is periplasm?

A

An extra compartment between the inner and outer membranes of gram-negative bacteria

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11
Q

How much of the cell volume is periplasmic compartment?

A

20-40%

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12
Q

What does the periplasmic compartment contain?

A

The cell wall and a gel-like solution of proteins that facilitate nutrition and inactivate toxic compounds

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13
Q

What does the periplasmic space allow?

A

Concentration of detoxifying enzymes

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14
Q

In gram-positive bacteria, where are the detoxifying antibodies secreted?

A

Into surrounding membrane

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15
Q

What is the cell membrane?

A

An osmotic barrier modified by the presence of specific transport systems

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16
Q

What makes up the cell membrane?

A

Phospholipid bilayers that lacks sterols

Embedded membrane proteins

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17
Q

What are the embedded membrane proteins?

A

Specific transport systems for secretion and uptake

Macromolecular synthesis/secretion proteins, such as cell wall Metabolic proteins: electron transport system

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18
Q

What is the cell membrane the site of?

A

Action of some disinfectants and detergents

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19
Q

What does peptidoglycan (cell wall) do?

A

Imparts cell shape and allows bacteria to survive in hypotonic solution

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20
Q

What is peptidoglycan?

A

The basic layer just outside the cell membrane in all eubcteria except Mycoplasma

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21
Q

What is peptidoglycan composed of?

A

A complex polymer forming concentric sheets

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22
Q

Is peptidoglycan thicker in gram-positive or gram-negative?

A

Gram-positive

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23
Q

What is peptidoglycan the site of action for?

A

Lysozyme and lysostaphin

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24
Q

What is a special component of gram-positive cell walls?

A

Teichoic/lipoteichoic acids

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25
Describe teichoic/lipoteichoic acids
Attached to peptidoglycan or anchored in the cytoplasmic membrane Can account for up to half of cell wall mass Species-specific structure Composed of sugar backbone with side groups Highly antigenic and useful as taxonomic markers
26
What are the 3 parts to peptidoglycan?
Backbone: alternating NAG and NAM monomers Side chains: tetrapeptides attached to NAM Crosslinkages: Linked side chains from peptides from different backbone units
27
What are the tetrapeptides attached to NAM?
D-alanine, L-alanine, D-glutamic acid, and L-lysine
28
What are crosslinkages the site of?
Penicillin action
29
How are gram-negative side chains linked?
Directly by interpeptide bonds
30
What are side chains like in many gram-positive bacteria?
They are crosslinked by an interpeptide bridge of amino acids
31
What do lipoproteins do?
Attach cell wall to outer membrane of gram-negative bacteria
32
What do the outer membrane proteins include of gram-negative bacteria?
Porins that allow nutrients to pass through | Many proteins involved in host-pathogen interaction
33
What is the inner leaflet of gram-negative bacteria made of?
Phospholipids
34
What is lipopolysaccharide?
Highly antigenic, species-specific and sometimes subspecies-specific structure
35
What does LPS induce?
A toxic response in mammals when release from lysed cells; hence it is also referred to as endotoxin
36
What are the 3 components of the unique bacterial structure of LPS?
``` Lipid A Core oligosaccharide O polysaccharide (O side chain or O antigen) ```
37
What is lipid A?
Hydrophobic portion that interacts with phospholipids inner leaflet This is the toxic portion of LPS
38
What is core oligosaccharide?
Short CHO chain attached to lipid A
39
What is O polysaccharide?
Long hydrophilic CHO chain attached to core oligosaccharide that covers the bacterial surface This is thee antigenic and serotype-specific structure of LPS
40
Where are capsules or slime layers?
Located outside the cell wall or outer membrane
41
What are capsules or slime layers?
Amorphous CHO polymers that vary widely from species to species in sugar composition and structure; often highly species or subspecies specific
42
What is the slime layer, more specifically?
The polymer that is loosely associated and continuously shed
43
What is the antigen involved with capsules?
K antigen
44
What are capsules and slime layers useful in? Why?
Serotyping and as vaccine antigens | They are immunogenic
45
What do capsules proivde?
An extra layer of protection for some bacteria by preventing lysosomal enzyme hydrolysis or complement-mediated lysis
46
In some bacteria, what can capsules serve as?
Adhesins, allowing adherence to epithelial surfaces
47
How are some capsules produced?
Only under certain conditions including in vivo
48
In some bacteria, what are capsules highly similar to?
The O polysaccharide
49
Describe the structure of Mycobacterium spp.
Gram-positive cell envelope structure, but cell wall contains mycolic acid and a large amount of lipids, which are complex, long-chain hydrocarbons substituted with sugars and other modifying groups
50
What does the acid-fast bacterial cell wall serve as?
A waxy, protective cover making them nearly impervious to many harsh chemicals
51
What do acid-fast bacterial cell walls prevent?
Penetration of gram stain reagents unless bacteria are pretreated with heat or a detergent
52
Why are acid-fast bacteria very slow growing?
The waxy coat causes slow uptake of nutrients
53
What is S layer?
Present on some fish pathogens | Located outside the cell wall or outer membrane
54
Describe S layer
Outer layer of protein subunits arranged in a crystalline array; usually a single king of protein molecule capable of self assembly Resistant to proteolystic enxymes and protein-denaturing agents Helps protect against phagocytosis and may participate in adherence to surfaces
55
What does the chlamydia cell envelope resemble?
The gram-negative envelope except they have no peptidoglycan layer
56
What does Chlamydia have instead of peptide crosslinkages?
A network of disulfied bonds among envelope proteins imparts rigidity to the chlamydial cell envelope
57
Describe Mycoplasma
Lack peptidoglycan cells wall; therefore, they are susceptible to osmotic lysis
58
What does the cytoplasm consist of?
A basic-staining, densely packed granular region surrounding an amorphous, less dense nuclear region
59
What is a chromosome?
Naked DNA
60
What is DNA of bacteria like?
Usually a circular, covalently closed double-stranded molecule
61
How many base pairs are in an E. coli chromosome? Protein coding genes?
4.6 million | 4288
62
How does a chromosome fit inside the bacteria cell?
It is highly supercoiled
63
What is a plasmid?
Smaller, accessory DNA molecules that replicated independently of the chromosome
64
What can plasmids sometimes be transferred between?
Bacterial cells
65
What do plasmids often carry?
Genes that confer a selective advantage under certain conditions (antibiotic resistance genes)
66
What are ribosomes?
Protein translation machinery
67
What gives the cytosol the granular appearance?
Dense packing of ribosomes
68
What is the structure of prokaryotic ribosomes?
70S, which can be dissociated into 50S and 30S subunits
69
What is used for classification of ribosomes?
16S
70
What is a polysome?
More than one ribosome can attach to a single mRNA strand
71
What is the target of several antibiotic classes?
Ribosomes
72
What allows ribosomes to be the target of several antibiotic classes?
The structural differences between prokaryotic and eukaryotic ribosomes
73
What is flagellum?
Organ of bacterial locomotion | Helical filament that is driven by a motor at its base
74
How does flagella rotate?
Relative to the bacterial surface to propel bacteria through the medium
75
What is the bacterial flagella like compared to eukaryotic flagella?
Bacteria is more rigid. Motion is by rotation only
76
What is monotrichous flagellum?
Has a single, polar flagellum (Vibrio cholerae)
77
What is peritrichous flagellum?
Has multiple flagella over their surface (E. coli)
78
What are the 3 parts of flagellum?
Filament Hook Basal body
79
What is the filament of flagellum?
Long, helical outermost structure extending into medium | Composed of several thousand copies of a single protein called flagellin
80
What are flagellins?
Highly antigenic proteins that have high immunologic specificity for H antigens
81
What does the hook do?
Connects filament to basal body
82
What does the basal body do?
Anchors in membrane, flagellar motor
83
What is the basal body driven by?
Protonmotive force (membrane potential)
84
What are attachment pili or fimbriae?
Organelles of attachment to surfaces | Hair-like projections extending from cell membrane
85
How many attachment pili/fimbriae does typical E. coli have?
100 to 300
86
What is attachment pili/fimbriae composed of?
Structural proteins called pilins and adhesin proteins at tip
87
What do adhesin proteins do?
Mediate attachment and exhibit remarkable specificity | Often are important virulence factors mediating attachment to host cell or extracellular matrix
88
What are the fimbriae of different bacteria like?
Antigenically distinct, so specific host antibodies can block attachment
89
What is conjugative pili?
Specialized organelles of plasmid DNA during conjugation (bacterial mating) Hollow tube connective 2 bacteria through which DNA is transferred
90
What can happen with antimicrobial resistance with a conjugative pili?
It can move from one bacteria to another
91
Describe endospores
Resting stag with high resistance to heat They are dehydrated cells composed of 5-15% calcium dipicolinate covered by keratin-like protein Extremely low metabolic activity, can survive for years in this state
92
What is the most resistance form of life known?
Endospores
93
What are L-forms?
A bacteria that lack a cell was the occurs spontaneously
94
Where may L-forms occur?
In vivo
95
What may L-forms be associated with?
Antibiotic resistance
96
What can induce formation of L-forms?
Special media with high osmolarity

Infectious Agents (38 decks)

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