AP-Micro Microbiology: Cell Structure and Function 3 — Questions and Answers
Question 1: Endospores produced by Bacillus and Clostridium species are extraordinarily resistant to heat. Which component is MOST responsible for this resistance?
- High water content in the core
- Dipicolinic acid chelated with calcium ions (Correct answer)
- Presence of a thick peptidoglycan layer
- High concentration of ATP in the spore core
Correct answer: Dipicolinic acid chelated with calcium ions
Dipicolinic acid (DPA) complexed with calcium ions replaces water in the spore core and stabilizes proteins and DNA against heat denaturation.
Question 2: Which eukaryotic cell structure is thought to have originated from an ancestral proteobacterium based on endosymbiotic theory?
- Nucleus
- Endoplasmic reticulum
- Mitochondrion (Correct answer)
- Golgi apparatus
Correct answer: Mitochondrion
Mitochondria are believed to have evolved from an alpha-proteobacterial endosymbiont, supported by evidence such as their own circular DNA, 70S ribosomes, and binary fission-like replication.
Question 3: What distinguishes S-layer proteins from other bacterial surface structures?
- They are composed of nucleic acids
- They form a two-dimensional crystalline array covering the cell surface (Correct answer)
- They are found only in gram-positive bacteria
- They function exclusively as adhesins for host attachment
Correct answer: They form a two-dimensional crystalline array covering the cell surface
S-layers are paracrystalline protein or glycoprotein arrays that self-assemble into a regular 2D lattice over the entire cell surface of many bacteria and archaea.
Question 4: A bacterium lacking a functional sec (secretion) pathway would MOST likely fail to:
- Replicate its chromosome accurately
- Translocate proteins across or into the cytoplasmic membrane (Correct answer)
- Synthesize peptidoglycan in the cytoplasm
- Transcribe mRNA from DNA templates
Correct answer: Translocate proteins across or into the cytoplasmic membrane
The Sec pathway is the primary general secretion system responsible for translocating unfolded proteins across the cytoplasmic membrane to the periplasm or cell surface.
Question 5: Teichoic acids are a defining component of which type of bacterial cell wall?
- Gram-negative outer membrane
- Gram-positive peptidoglycan layer (Correct answer)
- Mycobacterial mycolic acid layer
- Archaeal pseudopeptidoglycan
Correct answer: Gram-positive peptidoglycan layer
Teichoic acids are anionic polymers (wall teichoic acids and lipoteichoic acids) embedded in the thick peptidoglycan of gram-positive bacteria, contributing to surface charge and ion regulation.
Question 6: How does the periplasm of gram-negative bacteria differ from the cytoplasm?
- It contains ribosomes and is the site of translation
- It is a gel-like space between the inner and outer membranes containing degradative enzymes and binding proteins (Correct answer)
- It has a higher pH than the cytoplasm
- It is the primary location of chromosome replication
Correct answer: It is a gel-like space between the inner and outer membranes containing degradative enzymes and binding proteins
The periplasm is an aqueous compartment between the inner and outer membranes that contains a variety of enzymes (proteases, nucleases), binding proteins for nutrient uptake, and chemoreceptors.
Question 7: Which of the following structures is used by bacteria to transfer DNA during conjugation?
- Fimbriae
- Flagella
- Sex pilus (F-pilus) (Correct answer)
- Capsule
Correct answer: Sex pilus (F-pilus)
The sex pilus (encoded by the F plasmid) connects donor and recipient cells during conjugation, retracting to bring them together so that DNA can be transferred.
AP-Micro Microbiology: Cell Structure and Function 3
Endospores produced by Bacillus and Clostridium species are extraordinarily resistant to heat.
Which component is MOST responsible for this resistance?