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MCDB 131 > Lecture 3 - bacterial morphology & cell envelope structure > Flashcards

Lecture 3 - bacterial morphology & cell envelope structure Flashcards

1
Q

Morphologies that bacteria can take

A
  1. bacillus - rod shaped
  2. coccus - spherical
  3. spirochetes and spirilla - spiral
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2
Q

Example of bacilli

A

Lactobacillus lactus (used for milk cultures)

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3
Q
  • Borrelia burgdorgeri (causes Lyme disease)
  • Leptospira interrogans (cause of leptositosis)
A

Spirochetes

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4
Q

Examples of cocci

A

Streptococcus pneumoniae (cocci in pairs aka diplococci), anabaena spp (filaments of cyanobacteria)

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5
Q

What group of bacteria did mitochondria arise from?

A

Alpha-proteobacteria

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6
Q

Relationship between bacterial phylogeny and shape

A

There is not a clear relationship. Phylogenetically distant bacteria can take the same shape.

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7
Q
  • Stella vacuolata
  • Prosthecomicrobium
  • Ancalomicrobium adetum
A

Alpha-proteobacteria

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8
Q

Morphology of caulobacter

A

Curved with a holdfast stalk. Two differentiated cells before full division. Stalk cell has the holdfast. Other cell has a flagellum.

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9
Q

Morphology of streptomyces

A

Branched filamentous

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10
Q

Myces meaning

A

Myces = “fungi”

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11
Q

Strepto- meaning

A

Strepto = “chain of”
Therefore, streptococcus is a chain of cocci

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12
Q

Staphylo - meaning

A

Staphylo = “bunch of grapes”

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13
Q

What is one reason that bacterial morphology differs?

A

Can differ based on how the bacteria makes its cell wall

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14
Q

Significance of lack of bacterial intracellular compartments for DNA replication

A

Transcription and translation are not spatially or temporally separated like in eukaryotic cells.

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15
Q

Relationship between ribosome content and growth rate of bacteria

A

Higher ribosome content = higher growth rate
Ribosomes are generally the rate-limiting material in cell division

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16
Q

Common features of eubacterial cells

A
  • gel-like viscous cytoplasm; in dilute solutions, water wants to enter cell
  • circular chromosome in cytoplasm (nucleoid); takes up most of the cell’s volume
  • cell membrane of phosphoglycerolipids and protein
  • cell wall of peptidoglycan
  • organelles (ex: flagella, microcompartments)
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17
Q

Why do some bacteria have microcompartments?

A

Sequestration of enzymes or other material

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18
Q

Why is peptidoglycan highly conserved amongst bacteria?

A

Good for resisting osmotic pressure (prevents water from flooding into cell in dilute solutions)

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19
Q

Importance of lipopolysaccharides in bacterial outer membranes

A

Primary mechanism of bacterial interaction with host

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20
Q

Polyamines found in bacteria

A

Positively charged and protonated, act as counter-ions for DNA packing purposes
- Putrescine (smells like rotting fish due to same decaying amines)
- Spermine (discovered in sperm)

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21
Q

Why are two DNA molecules found per E.coli on average?

A

E. coli can replicate every 30 min, but the chromosome takes approx. 40 min to replicate

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22
Q

Gram-negative bacterial envelope structure

A

Two lipid membranes surrounding a thin layer of peptidoglycan cell wall

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23
Q

Gram positive bacterial envelope structure

A

One cell membrane under a multi-layered peptidoglycan wall. Can have an S-layer (surface layer). Glycosyl chains on exterior surface.

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24
Q

What do teichoic acids do?

A

Located in the peptidoglycan layer of Gram-positive bacteria. Contributes to wall stability and is responsible for retention of Gram stain

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25
Q

What are the two lipid membranes made of in Gram-negative bacteria?

A

Outer layer = lipopolysaccharide (LPS)
Inner layer = phospholipid

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26
Q

Major component of E. coli membrane (aside from phospholipid)

A

Proteins for material transport through the membrane

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27
Q

Composition of phosphoglycerides

A

Glycerol backbone + two fatty acids + phosphoryl head group through ester linkages.
Type of head group and fatty acid can be swapped out.

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28
Q

How do bacteria mediate their membrane fluidity?

A

Can change the fatty acids produced for their phospholipid membranes. Warmer temp –> increased saturation of fatty acid –> combat increased membrane fluidity

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29
Q

Why do saturated fatty acids in bacteria membranes fight against membrane fluidity?

A

More saturated = more straight –> tighter packing

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30
Q

What is cardiolipin?

A

Dimeric phospholipid (four fatty acid tails) discovered in cardiomyocytes.

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31
Q

Why was cardiolipin discovered in cardiomyocytes?

A

Cardiomyocytes require large amounts of energy for muscle contraction, therefore they have high amounts of mitochondria. Mitochondrial membrane is about 20% cardiolipin.

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32
Q

How is cardiolipin evidence for the bacterial origin of mitochondria?

A

In eukaryotic cells, mitochondria is the only source of cardiolipin. Cardiolipin is commonly found in bacterial membranes, thus mitochondria must have arisen from bacteria.

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33
Q

Why does passive diffusion of hydrophilic solutes across membranes require desolvation?

A

Activation energy for passive diffusion is very high for hydrophilic solutes. Without desolvation, it would take a very long time for it to diffuse across the membrane.

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34
Q

How are hydrophilic solutes moved across bacterial membranes?

A

Transporters interact with the solute to move it across without bringing water molecules with it.

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35
Q

How can weak acids and bases diffuse across membranes?

A

When not ionized, weak acids and bases are neutral and therefore are membrane-soluble

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36
Q

How do we know that weak acids and bases move through membranes?

A

Molecules like aspirin and penicillin are able to be taken up by cells for therapeutic purposes. We haven’t evolve receptors to transport these things, so they must be getting in to the cell through diffusion

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37
Q

Active vs passive transport

A

Passive transport: molecules move along concentration gradient
Active transport: energy is expended to move molecules against their concentration gradient (ex: glucose moves into cell, against its gradient, through primary or secondary active transport)

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38
Q

Primary vs secondary active transport

A

Primary: directly expends energy via ATP hydrolysis to transport molecule
Secondary: co-transports a molecule down it’s gradient to provide energy to move a molecule up its gradient

39
Q

What does the lac operon encode?

A

Encodes a lactose transporter (lactose permease) which allows lactose to pass through the membrane via secondary active transport

40
Q

ABC transporters

A

Ancient protein family found in all three branches of life. Uses ATP hydrolysis to facilitate primary active transport.

41
Q

What can ABC transporters move?

A
  • Vitamin B12, important for DNA synthesis.
  • Toxins and chemotherapeutic drugs
42
Q

How do human cells resist chemotherapy?

A

Upregulation of ABC transporters –> export of chemotherapeutic drugs from the cell

43
Q

Primary component of bacterial cell walls

A

Peptidoglycan (aka murein)

44
Q

What is peptidoglycan made out of?

A

Polymers of alternating N-acetyglucosamine and N-acetylmuramic acid sugars on a glycan strand.

45
Q

How is crosslinking facilitated in PG cell walls?

A

N-acetylmuramic acid residues carry peptides of 4-6 residues.

46
Q

Peptides found attached to N-acetylmuramic acid for crosslinking

A

L- alanine
D-Glutamic acid
m-Diaminopimelic acid
D-alanine
D-alanine

47
Q

How are N-acetylglucosamine and N-acetylmuramic acid linked?

A

1,4 beta linkage, very resistant to enzymatic breakdown

48
Q

How is cell wall rigidity regulated in bacterial cells?

A

Crosslinking of peptides

49
Q

What is capable of breaking bonds between N-acetylglucosamine and N-acetylmuramic acid?

A

Lysozyme can break 1,4 beta linkages and therefore acts as an antibacterial agent.

50
Q

Is lysozyme effective against all bacteria?

A

No. Lysozyme is only effective against Gram + bacteria due to their exposed PG wall. Gram - bacteria have an outer membrane protecting their PG

51
Q

How does penicilin act as an antibiotic?

A

Blocks release of the terminal D-alanine, preventing PG crosslinkages

52
Q

How does penicilin act as an antibiotic?

A

Blocks release of the terminal D-alanine, preventing PG crosslinkages

53
Q

How does vancomycin act as an antibiotic?

A

Binds D-Ala D-Ala and prevents the release of the terminal D-Ala

54
Q

Does vancomycin work on all bacteria?

A

Only works against Gram + with exposed PG because the molecule is too big to pass through the Gram - membrane

55
Q

How do bacteria become resistant to antibiotics?

A

Development of enzymes that degrade the antibiotic

56
Q

Beta-lactam antibiotics

A

Penicillins, cephalosporins, carbapenems

57
Q

What is the function of the bacterial cell wall?

A

Confers shape and rigidity and helps the cell withstand turgor pressure.

58
Q

Sacculus

A

Term for the single interlinked molecule that makes up the bacterial cell wall

59
Q

How does growth occur in the bacterial cell wall?

A

Formation of new glycan chains at the center of the bacteria, expanding outward. Requires the formation and breakdown of crossbridges between strands to make a single interlinked molecule

60
Q

Why are penicillins only useful against growing cells?

A

Disrupts the formation of new cross-linkages at the center of the bacteria. Weakens cell wall and causes lysis at the midpoint due to increased pressure from cell growth

61
Q

Function of the outer membrane of Gram - bacteria

A

Acts as a permeability barrier and contributes to the toxigenic properties of many pathogens (LPS is involved with the cell’s interaction with its environment)

62
Q

What links the cell wall to the outer membrane of Gram - bacteria?

A

Murein lipoprotein links to the peptides on N-acetylmuramic acid

63
Q

What is lipid A?

A

Lipid A is the highly conserved lipid portion of lipopolysaccharide (LPS) which is a toxic component of Gram - bacterial cell walls. Unlike other phospholipids, lipid A doesn’t have a glycerol phosphate backbone.

64
Q

How does the immune system recognize lipid A?

A

TLR-4 on innate immune cells recognizes lipid A to monitor for Gram - bacteria

65
Q

When does lipid A become problematic on its own?

A

If too much lipid A is released upon bacterial cell lysis, it can cause an overreaction from the immune system

66
Q

What are the components of LPS?

A

From bottom to top: lipid A, inner core, outer core, O antigen

67
Q

O antigen

A

Highly variable hydrophilic portion of LPS. Can be used to identify particular strains of bacteria

68
Q

Why is it important that O antigen is hydrophilic?

A

Blocks entrance of bile acids that would break down lipid membrane of Gram - bacteria

69
Q

Polymyxins

A

Detergent-like antibiotics that disrupt the outer membrane of Gram - bacteria

70
Q

How do polymyxins act as antibiotics?

A

Part cationic (hydrophilic) and part hydrophobic –> acts as a detergent

71
Q

What does O antigen dictate?

A

Host range of Gram - bacteria. Doesn’t have any control over toxicity.

72
Q

Why did E. coli K-12 lose its O antigen?

A

E. coli K-12 is a lab strain of E. coli that doesn’t live in a human host. Therefore, it didn’t need the O antigen to protect against bile acids and other enzymes. Loss of O antigen allowed for faster growth

73
Q

Structure of most porins

A

Made of beta barrels

74
Q

Function of E. coli OmpC

A

Cation-selective porin that allows passage of materials under 600 Daltons

75
Q

Examples of material moved by OmpC

A

Penicillin and beta lactam

76
Q

What was the origin of the name OmpC?

A

Outer membrane protein C

77
Q

What can induce the loss of OmpC and other porin expression?

A

Exposure to small antibiotic molecules. Loss of porin prevents transport of molecule into the cell

78
Q

PhoE

A

Trimeric porin that transports anions like phosphate into cell

79
Q

Tsx

A

Transporter of nucleosides. Receptor discovered in T6 phage

80
Q

Nucleoside

A

Dephosphorylated nucleotide

81
Q

LamB

A

Trimeric porin that transports maltose into the cell. Receptor discovered in lambda phage

82
Q

BtuB

A

“B twelve uptake”
Gated channel that transports vitamin B12

83
Q

TolC

A

Beta barrel protein that helps mediate export of antibiotics and toxins. Works with multiple different pumps

84
Q

TolC + HlyD and HlyB

A

HlyD and B uses primary active transport to move hemolysine to the periplasmic space for TolC uptake.
Result: export of hemolysine, molecule that lyses RBCs for bacterial iron uptake.

85
Q

TolC + AcrA and B

A

AcrA and B use secondary active transport (proton gradient used) to transport acridine and other hydrophobic drugs into the periplasmic space for TolC uptake. Result: export of acridine and other drug resistance

86
Q

What is a capsule (cell envelope)

A

Polysaccharide matrix that can be found surrounding Gram + bacteria. Usually, production of a capsule is stress-induced.

87
Q

What is an S-layer (cell envelope)

A

Surface protein layer that can be found on the surface of Gram + (and occasionally Gram -) bacteria. Proteins exported to surface and self-assemble into regular arrangements to protect against predation. Pores present at vertices of the arrangement to allow material transport.

88
Q

Teichoic acid structure

A

Polymers made of glycerol or ribitol linked by phosphodiester bonds. Amino acids and sugars can be found attached. Anionic.

89
Q

Teichoic acids vs lipoteichoic acids

A

Teichoic covalently linked to PG. Lipoteichoic linked to cell membrane and wall

90
Q

Mycobacterial cell envelope

A

Waxy and hydrophobic. Include unusual lipids and sugars (mycolic acids and arabinogalactans).

91
Q

Mycolic acids

A

Long, waxy lipids ~ 100 carbons long. Make tight permeability barriers for mycobacterial species. Causes slow growth of bacteria.

92
Q

Relationship between phylogeny and cell envelope structure

A

Unclear. Mycobacteria are closely related to Gram + species but use a very different envelope

93
Q

Average volume of a bacterial cell

A

1 femtolitre (fL0

MCDB 131 (15 decks)

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