Do you need to use lysozyme when purifying genomic DNA from Gram-negative bacteria in order to be successful?

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Question: Do you need to use lysozyme when purifying genomic DNA from Gram-negative bacteria in order to be successful?

Option 1: No, because lysozyme is targeting the numerous peptidoglycan layers in the cell wall of Gram-positive bacteria.
- This statement correctly describes the role of lysozyme in Gram-positive bacteria, which have thick peptidoglycan walls. However, it implies the same reasoning applies to Gram-negative bacteria, which is not accurate. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane that provides additional protection, so lysozyme is not as critical for disrupting their walls during genomic DNA purification. The statement is partly correct about Gram-positive targeting but misleading if applied to Gram-negative purification needs.

Option 2: Yes, lysozyme is essential in breaking down the cell wall of Gram-negative bacteria.
- This is not correct. Gram-negative bacteria possess an outer membrane that protects the peptidoglycan layer, making lysozyme less effective. In many standard genomic DNA preps for Gram-negative bacteria, lysozyme is not strictly essential, or may be omitted, and other reagents (e.g., detergent/abrupt lysis) are used to break cells. Claiming lysozyme is essential here overstates its role.

Option 3: Yes, lysozyme is critical in breaking down the cell membrane.
- This is incorrect because lysozyme does not target membranes; it enzymatically cleaves the β-1,4-glycosidic bonds in the peptidoglycan of bacterial cell walls. The cell membrane is not its primary substrate. Therefore, this option misstates the mechanism of action of lysozyme.

Option 4: No, because lysozyme is targeting the nucleus which Gram-negative bacteria lack.
- This is incorrect on multiple counts. Bacteria do not have a nucleus, and lysozyme does not target nuclei. The fundamental misunderstanding here makes this option false. Lysozyme acts on cell wall components, not any nuclear structure (which bacteria simply do not possess).

Summary: Analyzing these statements shows that the most accurate and relevant idea is that lysozyme is not essential for purifying genomic DNA from Gram-negative bacteria due to the outer membrane barrier and the fact that lysozyme mainly targets thick peptidoglycan seen in Gram-positive bacteria. The other options either misstate lysozyme’s target (membrane, nucleus) or overstate its essential role for Gram-negative cells.

BIOL2309.13196.202610 Quiz 3: DNA Purification and Quantification

Do you need to use lysozyme when purifying genomic DNA from Gram-negative bacteria in order to be successful?

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