Ch. 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 4 - Functional Anatomy of Prokaryotic and Eukaryotic Cells

Problem 4

Chapter 4, Problem 4

Use the following choices to answer the following question.
a. No change will result; the solution is isotonic.
b. Water will move into the cell.
c. Water will move out of the cell.
d. The cell will undergo osmotic lysis.
e. Sucrose will move into the cell from an area of higher concentration to one of lower concentration.

Which statement best describes what happens when a gram-positive bacterium is placed in an aqueous solution of lysozyme and 10% sucrose?

Verified step by step guidance

Understand the components involved: lysozyme is an enzyme that breaks down the peptidoglycan layer in bacterial cell walls, especially effective against gram-positive bacteria due to their thick peptidoglycan layer.

Recognize the role of 10% sucrose solution: a high concentration of sucrose creates a hypertonic environment outside the bacterial cell, which affects water movement by osmosis.

Analyze the effect of lysozyme on the gram-positive bacterium: lysozyme will degrade the peptidoglycan layer, weakening the cell wall and making the cell susceptible to osmotic pressure changes.

Consider the osmotic consequences: because the external solution is hypertonic (due to 10% sucrose), water tends to move out of the bacterial cell to the surrounding solution to balance solute concentrations.

Combine these effects to determine the outcome: the weakened cell wall from lysozyme action plus water moving out due to the hypertonic sucrose solution will cause plasmolysis (cell shrinkage), so water moves out of the cell.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Structure and Characteristics of Gram-Positive Bacteria

Gram-positive bacteria have a thick peptidoglycan cell wall that provides rigidity and protection. This wall is crucial for maintaining cell shape and preventing osmotic lysis. Unlike gram-negative bacteria, they lack an outer membrane, making their peptidoglycan layer more accessible to agents like lysozyme.

Mechanism of Action of Lysozyme

Lysozyme is an enzyme that breaks down the β-1,4-glycosidic bonds in peptidoglycan, weakening the bacterial cell wall. In gram-positive bacteria, lysozyme can degrade the thick peptidoglycan layer, compromising cell wall integrity and potentially leading to cell lysis if osmotic conditions favor water influx.

Osmotic Effects in Hypertonic Solutions

A 10% sucrose solution is hypertonic relative to the bacterial cytoplasm, causing water to move out of the cell by osmosis. This water loss can lead to plasmolysis, where the cell membrane shrinks away from the cell wall, preventing osmotic lysis despite cell wall damage from lysozyme.

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Compare and contrast the following:

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b. Active transport and facilitated diffusion

c. Active transport and group translocation

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Match the structures in column A to their functions in column B.

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Draw the bacterial shapes listed in (a), (b), and (c). Then draw the shapes in (d), (e), and (f), showing how they are special conditions of a, b, and c, respectively.

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Textbook Question

Use the following choices to answer the following question.

a. No change will result; the solution is isotonic.

b. Water will move into the cell.