교과서 질문
Helicobacter pylori uses the enzyme urease to counteract a chemical defense in the human organ in which it lives. This chemical defense is
a. lysozyme.
b. hydrochloric acid.
c. superoxide radicals.
d. sebum.
e. complement.
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19. Innate Immunity
First-Line Defenses: Chemical Barriers
Multiple Choice
How does lysozyme help kill or inhibit bacteria as part of the body’s first-line chemical defenses?
A
It inactivates bacterial ribosomes by cleaving rRNA, stopping protein synthesis.
B
It inserts into the bacterial cytoplasmic membrane to form pores, leading to leakage of ions and ATP.
C
It hydrolyzes the glycosidic bond between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in peptidoglycan, weakening the cell wall and causing lysis (especially in Gram-positive bacteria).
D
It binds to bacterial DNA ends and blocks DNA polymerase, preventing chromosome replication.
검증된 단계별 안내1
Understand that lysozyme is an enzyme that targets the bacterial cell wall, which is a critical structure for bacterial survival, especially in Gram-positive bacteria.
Recall that the bacterial cell wall is primarily composed of peptidoglycan, a polymer consisting of sugar chains cross-linked by peptides. The sugar chains include alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
Recognize that lysozyme acts by hydrolyzing the \( \beta-1,4 \) glycosidic bond between NAG and NAM in the peptidoglycan layer. This enzymatic cleavage breaks down the structural integrity of the cell wall.
Understand that weakening the peptidoglycan layer compromises the bacterial cell wall, making it unable to withstand osmotic pressure, which leads to cell lysis (bursting) and death of the bacterium.
Note that this mechanism is particularly effective against Gram-positive bacteria because they have a thick peptidoglycan layer exposed to the environment, whereas Gram-negative bacteria have an outer membrane that provides additional protection.
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