FIRST AID USMLE STEP 1: MICROBIOLOGY EXAM
2025 WITH ACCURATE SOLUTIONS
Cell Wall Overall Picture - Compare *Gram (+) to Gram
(-)* - CORRECT -
*Flagellum* on bacteria is composed of what? What is
the function? - CORRECT -Composition:
Proteins
Function: motility
*Pilus/Fimbria* on bacteria is composed of what? What is
the function? - CORRECT -Composition:
Glycoprotein
Function: Mediate adherence of bacteria to cell surface,
sex plus during conjugation.
*Spore* formation is ONLY possible is what type of
bacteria? Why is the formation of spores
important/beneficial?
,What is the composition of a spore? -
CORRECT -Gram Positive Only
Function: Resistant to dehydration, heat, and chemicals.
Composition: Keratin-like coat; dipicolinic acid;
peptidoglycan.
*Capsule* will be composed of what on bacteria? What is
the benefit of a capsule? - CORRECT -
Function: Protects against phagocytosis
Composition: Organized, discrete polysaccharide layer
(except Bacillus anthracis, which contains d-glutamate)
Glycocalyx - CORRECT -Function: Mediates
adherance to surfaces, especially foreign surfaces (e.g.,
indwelling catheters)
Composition:Loose network of polysaccharides
,Periplasm - CORRECT -Space between the
cytoplasmic membrane and outer membrane in gram-
negative bacteria
(peptidoglycan in the middle)
Gram Neg only
Accumulates components exiting gram neg cells,
including hydrolytic enzymes (β-lactamases)
Outer membrane (gram negatives) - CORRECT
-Gram Neg Only
Function:
1. Endotoxin: Lipid A induces TNF and IL-1; O
polysaccharide is antigenic
2. Most OMPs are antigenic
Porins: transport across outer membrane
Composition:
1. Outer Leaflet: endotoxin lipopolysaccharide
[LPS/LOS]
, 2. Embedded proteins: porins and other outer membrane
proteins (OMPs)
3. Inner Leaflet: phospholipids
Cell wall and Gram Stain - CORRECT -
Composition: Peptidoglycan is a sugar backbone with
peptide chains cross-linked by transpeptidase
Function: Net-like structure give rigid support, protects
against osmotic pressure damage.
Gram Stain:
Thick peptidoglycan layer retains crystal violet = gram +
Thin peptidoglycan layer turns red or pink with
counterstain = gram -
Cytoplasmic Membrane - CORRECT -
Composition: Phospholipid bilayer sac with embedded
proteins (PBP's) and other enzymes.
2025 WITH ACCURATE SOLUTIONS
Cell Wall Overall Picture - Compare *Gram (+) to Gram
(-)* - CORRECT -
*Flagellum* on bacteria is composed of what? What is
the function? - CORRECT -Composition:
Proteins
Function: motility
*Pilus/Fimbria* on bacteria is composed of what? What is
the function? - CORRECT -Composition:
Glycoprotein
Function: Mediate adherence of bacteria to cell surface,
sex plus during conjugation.
*Spore* formation is ONLY possible is what type of
bacteria? Why is the formation of spores
important/beneficial?
,What is the composition of a spore? -
CORRECT -Gram Positive Only
Function: Resistant to dehydration, heat, and chemicals.
Composition: Keratin-like coat; dipicolinic acid;
peptidoglycan.
*Capsule* will be composed of what on bacteria? What is
the benefit of a capsule? - CORRECT -
Function: Protects against phagocytosis
Composition: Organized, discrete polysaccharide layer
(except Bacillus anthracis, which contains d-glutamate)
Glycocalyx - CORRECT -Function: Mediates
adherance to surfaces, especially foreign surfaces (e.g.,
indwelling catheters)
Composition:Loose network of polysaccharides
,Periplasm - CORRECT -Space between the
cytoplasmic membrane and outer membrane in gram-
negative bacteria
(peptidoglycan in the middle)
Gram Neg only
Accumulates components exiting gram neg cells,
including hydrolytic enzymes (β-lactamases)
Outer membrane (gram negatives) - CORRECT
-Gram Neg Only
Function:
1. Endotoxin: Lipid A induces TNF and IL-1; O
polysaccharide is antigenic
2. Most OMPs are antigenic
Porins: transport across outer membrane
Composition:
1. Outer Leaflet: endotoxin lipopolysaccharide
[LPS/LOS]
, 2. Embedded proteins: porins and other outer membrane
proteins (OMPs)
3. Inner Leaflet: phospholipids
Cell wall and Gram Stain - CORRECT -
Composition: Peptidoglycan is a sugar backbone with
peptide chains cross-linked by transpeptidase
Function: Net-like structure give rigid support, protects
against osmotic pressure damage.
Gram Stain:
Thick peptidoglycan layer retains crystal violet = gram +
Thin peptidoglycan layer turns red or pink with
counterstain = gram -
Cytoplasmic Membrane - CORRECT -
Composition: Phospholipid bilayer sac with embedded
proteins (PBP's) and other enzymes.
