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MBIO1010 > Lecture Set 2 : Part 2 > Flashcards

Lecture Set 2 : Part 2 Flashcards

1
Q

what is the bacterial cell wall?

A

-outside the cell membrane
-rigid (due to peptidoglycan)
-helps to determine cell shape
-not a major permeability barrier (porous to most small molecules)

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2
Q

what is the purpose of the cell wall being a rigid structure?

A

-provides structural support for the physically weaker cell membrane

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3
Q

what does the bacterial cell wall protect the cell from?

A

-cell expansion due to osmotic changes (osmotic lysis)
-toxic substances (large hydrophobic molecules like detergents and antibiotics)

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4
Q

how does the cell wall aid in pathogenicity?

A

-helps evade the host’s immune system (protects them from typical defences)
-helps bacterium stick to surfaces (polysaccharides + glycoproteins in its structure)

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5
Q

what is pathogenicity?

A

-the ability of an organism to cause disease

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6
Q

how can we separate bacteria into 2 groups?

A

-structure of their cell walls
-gram positive and gram negative cells

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7
Q

what is contained within both gram positive and gram negative cell walls?

A

-complex macromolecule peptidoglycan
-formerly known as murein (later used in archaeal cell walls as pseduomurein)

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8
Q

what is contained within the cell walls of gram positive cells?

A

-thick layer of peptidoglycan

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9
Q

what is contained within the cell walls of gram negative cells?

A

-thin layer of peptidoglycan
-outer membrane

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10
Q

what is the peptidoglycan structure in a gram negative cell of E.coli?

A

-chain of 2 alternating sugars linked by Beta 1,4 glycosidic bonds (glycan chain) (consistent for all)
-N - acetylglucosamine (G)
-N - acetylmuramic acid (M)
-glycan tetrapeptide (4 amino acids) is attached to NAM
-glycan tetrapeptide = L-Alanine, D-Glutamate, DAP, D-Alanine (linked by covalent peptide bonds)
-there is always a peptide, how many + specific amino acids vary
-forms a mesh-like structure around the cell 10-20% of the time (2 parallel strands)

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11
Q

what features of peptidoglycan in a gram negative cell of E.coli make it difficult to break down?

A

-B-1,4 glycosidic bonds are stronger than alpha bonds in other glycans (ie. starch and glycogen)
-unusual amino acids in the tetrapeptide (D amino acids are not usually found in proteins, mostly L amino acids) (makes it resistant to most peptidases)

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12
Q

what are peptidases?

A

-enzymes that cleave peptide bonds to break apart proteins

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13
Q

how is peptidoglycan organized to form its mesh structure in a gram negative cell of E.coli?

A

-DAP is linked to the D-Alanine of an adjacent peptidoglycan strand
-forms a cross-link between strands

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14
Q

how do the bonds in peptidoglycan of a gram negative cell of E.coli increase strength?

A

-glycosidic bonds increase horizontal strength
-peptide bonds increase vertical strength

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15
Q

what is the peptidoglycan structure in a gram positive cell of Staphylococcus aureus?

A

-chain of 2 alternating sugars linked by Beta 1,4 glycosidic bonds (glycan chain) (consistent for all)
-N - acetylglucosamine (G)
-N - acetylmuramic acid (M)
-glycan tetrapeptide (4 amino acids) is attached to NAM
-glycan tetrapeptide = L-Alanine, D-Glutamine, L-lysine, D-Alanine (linked by covalent peptide bonds)
-there is always a peptide, how many + specific amino acids vary
-cross-link is a pentaglycine (5) peptide interbridge (kind of peptide + #’s differ with species)
-more heavily cross-linked (90%) of the time

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16
Q

how does the peptide interbridge of a gram positive cell of staphylococcus aureus connect the 2 strands?

A

-the bottom glycine connects to the D-Alanine of one strand
-the top glycine connects to the L-lysine of the opposite strand

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17
Q

how many peptidoglycan structures have been identified? how are they similar? how do they differ?

A

-more than 100
-all have N-acetylglucosamine and N-acetylmuramic acid connecting to the peptide chain
-vary in peptide cross links or interbridge

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18
Q

what form does the peptidoglycan strand have? what is this used for?

A

-helical
-allows 3D crosslinking

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19
Q

how many layers of peptidoglycan does E.coli have? how many do gram negative cells have in general?

A

-1 layer (E.coli)
-1-3 layers (general)

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20
Q

how many layers of peptidoglycan do gram positive cells have generally? what is an example of one with a very thick amount?

A

-15+
-bacillus species can have 50-100 layers

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21
Q

what makes peptidoglycan important?

A

-it is only found in bacteria
-presents a structure that can be targeted without harming humans (selective damage)
-particularly is important when it comes to certain drugs/antibiotics

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22
Q

what is selective toxicity?

A

-only toxic to your target
-will not be toxic to the host

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23
Q

what are 2 defences against bacteria that specifically target peptidoglycan?

A

-lysozyme
-penicillin

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24
Q

how does lysozyme target peptidoglycan?

A

-specifically cleaves B-1,4 glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid
-can cause cell lysis (lack control against osmotic change)
-destroys pre-existing peptidoglycan

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25
where is lysozyme found?
-tears, saliva, nasal secretions (bodies natural defences)
26
how does penicillin target peptidoglycan?
-antibiotic that prevents the formation of peptidoglycan cross-links -inhibits penicillin binding proteins -prevents the mesh structure from being built (no resistance against osmotic pressure) -cells burst due to osmotic pressure (lysis) -destroys the formation of peptidoglycan
27
what are the specific characteristics of the gram positive cell wall?
-thick layers of peptidoglycan (15+) -contains wall teichoic and lipiteichoic acids (not present in gram negatives)
28
what are wall teichoic acids?
-attached to the peptidoglycan (do not touch the cell membrane) -can extend outward or just be within the peptidoglycan -helps to give the surface of cells its negative charge
29
what are lipoteichoic acids?
-teichoic acid with a lipid connected at one end (lipid is from the cytoplasmic membrane) -links the peptidoglycan to the cytoplasmic membrane
30
what does the thick layer of peptidoglycan allow for in gram positive cells?
-allows for staining to hold
31
what are the specific characteristics of the gram negative cell wall?
-1-3 layers of petidoglycan (thin) surrounded by an outer membrane -the area between the outer membrane and cytoplasmic membrane is the periplasmic space
32
what can you also call the cytoplasmic membrane in a gram negative cell wall?
-the inner membrane
33
what are the characteristics of the outer membrane?
-true unit membrane (phospholipid bilayer) -inner leaflet is formed by ester phospholipids -outer leaflet is mostly lipopolysaccharides (LPS) + phospholipids in a smaller quantity -contains outer membrane proteins (differ from cytoplasmic membrane proteins) -impedes movement of large molecules (antibiotics + detergents)
34
what are the inner and outer leaflets of the outer membrane and the inner membrane?
-outer leaflet of the outer membrane is the outermost layer -inner leaflet of the outer membrane is next to the peptidoglycan/periplasm outer leaflet of the inner membrane is next to the peptidoglycan/periplasm -inner leaflet of the inner membrane is next to the cytoplasm
35
how do outer membrane proteins and cytoplasmic membrane proteins differ?
-differ in function -each membrane has different needs
36
what are lipopolysaccharides?
-3 components -makes up most of the outer leaflet of the outer membrane -endotoxin
37
what are the 3 components of lipopolysaccharides?
-lipid A -core polysaccharide -O-specific polysaccharide
38
what is the lipid A portion of a lipopolysaccharide?
-composed of sugars, phosphates, and fatty acid -portion embedded in the membrane (outer leaflet) -toxic to animals + humans if it becomes exposed
39
what is the core polysaccharide of a lipopolysaccharide?
-sugars that stay relatively constant in gram negative bacteria
40
what is the O-specific polysaccharide of a lipopolysaccharide?
-long chain of sugars -highly variable -forms a major surface antigen (identifier) (O-antigen)
41
how does the O-specific polysaccharide vary throughout species and strains?
-different strains within the same species can have different O-antigens -same strain can have different presentations of its O-antigen (2 sugars as the O-sugar, can present 1, both, or neither) (changes survival advantages)
42
what happens when a gram negative bacterium dies that makes it an endotoxin?
-the outer membrane breaks apart and LPS is released -the Lipid-A can become exposed -disease symptoms can occur (vomiting, diarrhea, and shock) -important in gastrointestinal pathogens (ex: E.coli + salmonella)
43
what is a situation where a gram negative bacteria can act as an endotoxin?
-when taking some antibiotics the bacteria is kills and may release lipid-A (increasing symptoms) -lipid-A is fine as long as it is embedded
44
what are porins?
-outer membrane protein -typically 3 protein subunits that make a trimer -forms a channel through the outer membrane -allows the movement of small hydrophilic molecules (nutrients)
45
what is the periplasm?
-space between the cytoplasmic membrane and the outer membrane (15nm) -peptidoglycan resides here -area of high metabolic activity (has proteins that are distinct from the cytoplasm)
46
what proteins are contained within the periplasm?
-substrate binding proteins -hydrolytic enzymes -biosynthetic enzymes
47
what is the function of substrate binding proteins within the periplasm?
-bind substrates and move them to the cytoplasmic membrane for transport into the cell (ABC transporter)
48
what is the function of hydrolytic enzymes within the periplasm?
-degrade foreign substances -ex: endonucleases
49
what is the purpose of endonucleases?
-destroy foreign DNA
50
what is the function of biosynthetic enzymes?
-cell wall synthesis -ex: penicillin binding proteins
51
what is the purpose of penicillin binding proteins?
-involved in the cross-linking of peptidoglycan -can be inhibited by penicillin (disrupts cell wall synthesis)
52
what are the characteristics of archaeal cell walls?
-do not contain peptidoglycan or an outer membrane -made of polysaccharide, protein, glycoprotein, or other complex macromolecules -common wall type is the S-layer -protects against osmotic pressure (lysis) -porous to small molecules -can block larger molecules
53
what is the S-layer of an archaeal cell wall?
-paracrystaline surface layer -layer of interlocking proteins or glycoproteins -can help to retain periplasmic proteins -some cells have
54
how does the S-layer help to retain periplasmic proteins? what does this allow for?
-S-layer can create a periplasmic-like space between it and the cytoplasmic membrane -allows for important cellular reactions associated with metabolism to occur
55
what may other archaeal cell walls be built from?
-pseudomurein (complex peptidoglycan-like structure) -no N-acetylmuramic acid (N-acetyltalosaminuronic instead) (T) -B-1,3 bonds between sugars instead of B-1,4 -L-amino acids (no D-amino acids, more typical) -can cause them to stain purple (gram positive)
56
if an archaeal cell wall has an S-layer and another layer, which will be most exterior?
-S-layer will be most exterior
57
what defences do not work against archaeal cell walls made from pseudomurein that worked for bacteria cell walls?
-pseudomurein in general is not targeted by drugs/antibiotics -not degraded by lysozyme (contain B-1,3 bonds instead of B-1,4) -L-amino acids which can be affected by peptidases -cross-link formation is not inhibited by penicillin
58
why is the lack of defence against archaea not a worry?
-there are no pathogenic archaea
59
what is an example of a bacteria that lacks a cell wall?
-mycoplasmas (mycoplasma genitalium, can cause an STI) -pathogen of humans and animals (live inside) -osmotic protection is supplied by the host -cytoplasm of the host will be osmotically similar to the bacteria -has sterols in its cytoplasmic membrane (for strength + rigidity) (compensates for a lack of cell wall)
60
what is an example of an archaea that lacks a cell wall?
-thermoplasma -extremophiles that have a tetraether lipid monolayer cytoplasmic membrane (lipoglycan) -allows it to resist hot and acidic environments (already has strong resistance)

MBIO1010 (28 decks)

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