AP-Micro Microbiology: Cell Structure and Function 2 — Questions and Answers
Question 1: Which structural feature allows gram-negative bacteria to be inherently resistant to many antibiotics like penicillin?
- Thicker peptidoglycan layer
- Outer membrane containing LPS (Correct answer)
- Absence of a cell wall
- Presence of efflux pumps only
Correct answer: Outer membrane containing LPS
The outer membrane of gram-negative bacteria acts as a permeability barrier that excludes many antibiotics, including penicillin, from reaching the peptidoglycan layer.
Question 2: Bacterial flagella rotate to produce movement. Which component anchors the flagellum to the cell membrane and generates torque?
- Hook
- Filament
- Basal body (Correct answer)
- Cap protein
Correct answer: Basal body
The basal body is embedded in the cell membrane and wall, functioning as a motor that uses proton motive force to rotate the flagellum.
Question 3: A microbiologist observes a bacterium with fimbriae. What is the PRIMARY function of these structures?
- Locomotion through liquid media
- Attachment to host cell surfaces (Correct answer)
- DNA transfer between cells
- Protection against phagocytosis
Correct answer: Attachment to host cell surfaces
Fimbriae (also called pili) are short, hair-like appendages that mediate adhesion of bacteria to host tissues and surfaces.
Question 4: What is the function of porins found in the outer membrane of gram-negative bacteria?
- Actively pump ions using ATP
- Form channels that allow passive diffusion of small molecules (Correct answer)
- Synthesize lipopolysaccharide
- Anchor flagella to the membrane
Correct answer: Form channels that allow passive diffusion of small molecules
Porins are transmembrane proteins that form water-filled channels permitting passive diffusion of small hydrophilic molecules across the outer membrane.
Question 5: Which of the following correctly describes the nucleoid region of a prokaryotic cell?
- A membrane-bound organelle containing linear chromosomes
- A region containing circular DNA not enclosed by a membrane (Correct answer)
- A structure equivalent to the eukaryotic nucleus with a double membrane
- A specialized compartment for ribosome synthesis
Correct answer: A region containing circular DNA not enclosed by a membrane
The nucleoid is an irregularly shaped region in prokaryotes where the circular chromosomal DNA is compacted, but it lacks a surrounding membrane.
Question 6: Magnetotactic bacteria contain magnetosomes. What are magnetosomes and what is their cellular classification?
- Protein complexes on the cell surface; considered part of the glycocalyx
- Membrane-enclosed crystals of iron minerals; considered organelles (Correct answer)
- Lipid storage droplets; considered inclusion bodies
- RNA-protein complexes; considered ribosomes
Correct answer: Membrane-enclosed crystals of iron minerals; considered organelles
Magnetosomes are membrane-bound organelles containing magnetite or greigite crystals that allow bacteria to orient along geomagnetic fields.
Question 7: A student claims that all prokaryotes lack a cytoskeleton. Why is this claim incorrect?
- Prokaryotes have actin and tubulin identical to eukaryotes
- Prokaryotes have homologs such as MreB and FtsZ that function similarly to eukaryotic cytoskeletal proteins (Correct answer)
- Prokaryotes use flagella as a cytoskeletal framework
- Prokaryotes have intermediate filaments but not microfilaments
Correct answer: Prokaryotes have homologs such as MreB and FtsZ that function similarly to eukaryotic cytoskeletal proteins
Prokaryotes possess cytoskeletal homologs like MreB (actin homolog) that maintains cell shape and FtsZ (tubulin homolog) that forms the division ring during binary fission.
AP-Micro Microbiology: Cell Structure and Function 2
Which structural feature allows gram-negative bacteria to be inherently resistant to many antibiotics like penicillin?