BIOL 2051 Exam 2 Louisiana State University and
Agricultural & Mechanical College Questions with 100%
Verified Answers Latest Update
Question: Why are Gram stains NOT the most accurate method for diagnosing fungal (yeast)
infections, specifically Candida sps.?
Answer:
Gram staining is meant for bacteria, not fungi. Since fungal cell walls don't have
peptidoglycan, Gram stains give inconsistent or misleading results.
Question: Do antibiotics work for treating a yeast infection? Explain.
Answer:
No, because there is no peptidoglycan layer, which is what antibiotics target.
Question: What is the fungal cell wall composed of?
Answer:
chitin, β-glucan, and mannoproteins
Question: What is the role of chitin?
Answer:
a polysaccharide that provides strength and rigidity to the fungal cell wall
Question: What is a PG-cleaving (cutting) enzyme that is found in tears, mucus, saliva, and
egg whites?
Answer:
lysozyme
Question: Lysozyme, an enzyme in tears, helps us do what?
Answer:
fight infection; serves as the first line of defense in terms of immunity
Question: ___________ chrysogenum and ______________ chrysogenum are fungi that produce
antibiotics.
Answer:
Penicillium; Acremonium
Question: Lysozyme cleaves the bond between . . .
, Answer:
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), the alternating sugar subunits
of peptidoglycan.
Question: When lysozyme cleaves (cuts) the β-(1→4) bond — the bond between the sugar
monomers NAG and NAM — what happens?
Answer:
The bacterial cell wall weakens, and the cell undergoes lysis.
Question: What is the role of the enzyme glucosaminidase in bacterial cell remodeling?
Answer:
breaks bonds between sugar residues (helps remodel sugars)
Question: What is the role of the enzyme lytic transglycosylase in bacterial cell remodeling?
Answer:
helps reshape PG chains by cutting sugar linkages differently from lysozyme
Question: What is the role of the enzyme amidase in bacterial cell remodeling?
Answer:
separates peptide cross-links at the base of PG (NAM-peptide bond)
Question: What is the role of the enzyme carboxypeptidase in bacterial cell remodeling?
Answer:
trims peptide tails (controls PG cross-linking)
Question: What is the role of the enzyme endopeptidase in bacterial cell remodeling?
Answer:
cuts within peptide cross-links of the PG mesh
Question: Does bacteria need the enzymes to recycle/synthesize PG layer?
Answer:
Yes, bacteria must use their own controlled versions of these enzymes to remodel PG during
growth/division, recycle old cell wall material, and maintain cell wall integrity.
Question: Which type of bacteria is most affected by antibiotics that inhibit peptidoglycan
(PG) synthesis?
Answer:
,Gram-positive
Question: Why are drugs that target the bacterial peptidoglycan layer considered
selectively toxic to bacteria but not harmful to humans?
Answer:
Humans don't have a peptidoglycan cell wall, so these antibiotics only affect bacterial cells.
Question: What is the result when an antibiotic inhibits peptidoglycan synthesis in bacteria?
Answer:
Cell wall weakens and undergoes lysis
Question: Why aren’t 70S ribosome-targeting antibiotics always the safest option for
humans?
Answer:
Because human mitochondria also contain 70S-like ribosomes, these drugs could cause
mitochondrial damage or toxicity.
Question: Who is credited with the discovery of penicillin?
Answer:
Sir Alexander Fleming
Question: Penicillin blocks peptidoglycan (PG) layer synthesis by inactivating what?
Answer:
transpeptidase enzyme
Question: Transpeptidase active → _________________ → Strong cell wall forms → Bacterium
survives
When penicillin is present: Penicillin inactivates transpeptidase → ________________ → Weak
cell wall → Cell lysis (death)
Answer:
PG chains cross-linked; No cross-linking
Question: Why can’t penicillin easily inhibit the growth of Haemophilus influenzae or
Salmonella?
Answer:
Their outer membrane prevents penicillin entry.
Question: Explain why Gram-positive bacteria are more sensitive to penicillin than
Gram-negative bacteria.
, Answer:
Gram-positive bacteria lack an outer membrane, allowing penicillin to reach the
transpeptidase enzyme in the thick peptidoglycan layer. Gram-negative bacteria have an
outer lipid membrane that blocks penicillin entry.
Question: T or F: Bacillus anthracis and Staphylococcus are both endospore-forming
bacteria.
Answer:
False; Bacillus anthracis forms endospores, but Staphylococcus does not.
Question: T or F: Gram-negative bacteria have a thick peptidoglycan layer that allows easy
penetration by penicillin.
Answer:
False; They have a thin peptidoglycan layer and an outer membrane that blocks penicillin.
Question: In the inhibition plate shown in the notes, Staphylococcus, Streptococcus, Bacillus
anthracis had visible zones of inhibition due to penicillin. Explain this.
Answer:
Penicillin could not inhibit growth because the lipid layer (hydrophobic) prevented it from
entering.
Question: Yeast has _________ which is NOT affected by penicillin treatment.
Answer:
chitin
Question: Antibiotics such as penicillin and cephalosporins have a __________ ring that
normally binds to transpeptidase (PBP), causing lysis.
Answer:
β-lactam
Question: What does MRSA stand for?
Answer:
methicillin-resistant Staphylococcus aureus
Agricultural & Mechanical College Questions with 100%
Verified Answers Latest Update
Question: Why are Gram stains NOT the most accurate method for diagnosing fungal (yeast)
infections, specifically Candida sps.?
Answer:
Gram staining is meant for bacteria, not fungi. Since fungal cell walls don't have
peptidoglycan, Gram stains give inconsistent or misleading results.
Question: Do antibiotics work for treating a yeast infection? Explain.
Answer:
No, because there is no peptidoglycan layer, which is what antibiotics target.
Question: What is the fungal cell wall composed of?
Answer:
chitin, β-glucan, and mannoproteins
Question: What is the role of chitin?
Answer:
a polysaccharide that provides strength and rigidity to the fungal cell wall
Question: What is a PG-cleaving (cutting) enzyme that is found in tears, mucus, saliva, and
egg whites?
Answer:
lysozyme
Question: Lysozyme, an enzyme in tears, helps us do what?
Answer:
fight infection; serves as the first line of defense in terms of immunity
Question: ___________ chrysogenum and ______________ chrysogenum are fungi that produce
antibiotics.
Answer:
Penicillium; Acremonium
Question: Lysozyme cleaves the bond between . . .
, Answer:
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), the alternating sugar subunits
of peptidoglycan.
Question: When lysozyme cleaves (cuts) the β-(1→4) bond — the bond between the sugar
monomers NAG and NAM — what happens?
Answer:
The bacterial cell wall weakens, and the cell undergoes lysis.
Question: What is the role of the enzyme glucosaminidase in bacterial cell remodeling?
Answer:
breaks bonds between sugar residues (helps remodel sugars)
Question: What is the role of the enzyme lytic transglycosylase in bacterial cell remodeling?
Answer:
helps reshape PG chains by cutting sugar linkages differently from lysozyme
Question: What is the role of the enzyme amidase in bacterial cell remodeling?
Answer:
separates peptide cross-links at the base of PG (NAM-peptide bond)
Question: What is the role of the enzyme carboxypeptidase in bacterial cell remodeling?
Answer:
trims peptide tails (controls PG cross-linking)
Question: What is the role of the enzyme endopeptidase in bacterial cell remodeling?
Answer:
cuts within peptide cross-links of the PG mesh
Question: Does bacteria need the enzymes to recycle/synthesize PG layer?
Answer:
Yes, bacteria must use their own controlled versions of these enzymes to remodel PG during
growth/division, recycle old cell wall material, and maintain cell wall integrity.
Question: Which type of bacteria is most affected by antibiotics that inhibit peptidoglycan
(PG) synthesis?
Answer:
,Gram-positive
Question: Why are drugs that target the bacterial peptidoglycan layer considered
selectively toxic to bacteria but not harmful to humans?
Answer:
Humans don't have a peptidoglycan cell wall, so these antibiotics only affect bacterial cells.
Question: What is the result when an antibiotic inhibits peptidoglycan synthesis in bacteria?
Answer:
Cell wall weakens and undergoes lysis
Question: Why aren’t 70S ribosome-targeting antibiotics always the safest option for
humans?
Answer:
Because human mitochondria also contain 70S-like ribosomes, these drugs could cause
mitochondrial damage or toxicity.
Question: Who is credited with the discovery of penicillin?
Answer:
Sir Alexander Fleming
Question: Penicillin blocks peptidoglycan (PG) layer synthesis by inactivating what?
Answer:
transpeptidase enzyme
Question: Transpeptidase active → _________________ → Strong cell wall forms → Bacterium
survives
When penicillin is present: Penicillin inactivates transpeptidase → ________________ → Weak
cell wall → Cell lysis (death)
Answer:
PG chains cross-linked; No cross-linking
Question: Why can’t penicillin easily inhibit the growth of Haemophilus influenzae or
Salmonella?
Answer:
Their outer membrane prevents penicillin entry.
Question: Explain why Gram-positive bacteria are more sensitive to penicillin than
Gram-negative bacteria.
, Answer:
Gram-positive bacteria lack an outer membrane, allowing penicillin to reach the
transpeptidase enzyme in the thick peptidoglycan layer. Gram-negative bacteria have an
outer lipid membrane that blocks penicillin entry.
Question: T or F: Bacillus anthracis and Staphylococcus are both endospore-forming
bacteria.
Answer:
False; Bacillus anthracis forms endospores, but Staphylococcus does not.
Question: T or F: Gram-negative bacteria have a thick peptidoglycan layer that allows easy
penetration by penicillin.
Answer:
False; They have a thin peptidoglycan layer and an outer membrane that blocks penicillin.
Question: In the inhibition plate shown in the notes, Staphylococcus, Streptococcus, Bacillus
anthracis had visible zones of inhibition due to penicillin. Explain this.
Answer:
Penicillin could not inhibit growth because the lipid layer (hydrophobic) prevented it from
entering.
Question: Yeast has _________ which is NOT affected by penicillin treatment.
Answer:
chitin
Question: Antibiotics such as penicillin and cephalosporins have a __________ ring that
normally binds to transpeptidase (PBP), causing lysis.
Answer:
β-lactam
Question: What does MRSA stand for?
Answer:
methicillin-resistant Staphylococcus aureus
