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Microbiolgy > Lecture 4: Gram staining and Peptidoglycan > Flashcards

Lecture 4: Gram staining and Peptidoglycan Flashcards

1
Q

What is the primary stain used in Gram staining?

A

Crystal violet

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2
Q

What role does Gram’s iodine play in Gram staining?

A

Binds crystal violet

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3
Q

What is the decolorizer used in Gram staining?

A

Acetone or ethanol

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4
Q

What color do Gram-positive bacteria appear after staining?

A

Purple

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5
Q

What color do Gram-negative bacteria appear after staining?

A

Colorless

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6
Q

What is the secondary stain used in Gram staining?

A

Safranin

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7
Q

What color does safranin turn Gram-negative cells?

A

Red/pink

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8
Q

What are the two main components of peptidoglycan?

A

NAG and NAM

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9
Q

What does NAG stand for?

A

N-acetylglucosamine

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10
Q

What does NAM stand for?

A

N-acetylmuramic acid

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11
Q

List the amino acids found in the tetrapeptide of peptidoglycan.

A
  • L-alanine
  • D-glutamic acid
  • meso-DAP (or L-lysine)
  • D-alanine
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12
Q

What is the structure of peptidoglycan described as?

A

Very large molecule of repeating units

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13
Q

What forms the backbone of peptidoglycan?

A

Alternating NAG and NAM strands

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14
Q

What is attached to NAM in the structure of peptidoglycan?

A

Tetrapeptide (L-ala, D-glu, M-DAP, D-ala)

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15
Q

How are NAG/NAM strands cross-linked in peptidoglycan?

A

By covalent bonds between the tetrapeptides extending from each sugar strand

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16
Q

What additional feature does Gram-positive peptidoglycan have?

A

Peptide interbridge

17
Q

What is the mode of action of penicillin?

A

Prevents cross-linking of adjacent glycan chains

18
Q

Why is penicillin usually more effective against Gram-positive bacteria?

A

Outer membrane of Gram-negatives blocks access

19
Q

What is a characteristic of penicillins?

A

They have β-lactam rings

20
Q

What does the β-lactam ring bind to?

A

Enzymes that crosslink the peptidoglycan (tetrapeptides)

21
Q

What is lysozyme?

A

An enzyme that targets peptidoglycan

22
Q

Do penicillin and lysozyme affect Mycoplasma species?

A

No, they lack a cell wall

23
Q

What do Mycoplasma species contain in their cytoplasmic membrane?

A

Sterols that increase strength

24
Q

What is a defining characteristic of Archaea cell walls?

A

They vary widely and do not contain peptidoglycan

25
Q

What is pseudopeptidoglycan?

A

A similar molecule to peptidoglycan found in some Archaea

26
Q

What are S-layers in Archaea?

A

Built from sheets of flat protein or glycoprotein subunits

Microbiolgy (4 decks)

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