Final answer:
The major difference between exotoxins and endotoxins is that endotoxins are physically part of the bacterial structure, part of the LPS in gram-negative bacteria, whereas exotoxins are proteins secreted by bacteria and have specific cellular targets.
Step-by-step explanation:
A major difference between exotoxins and endotoxins is that endotoxins are physically part of the bacterial structure. Endotoxin, specifically known as lipid A, is a component of the lipopolysaccharide (LPS) of the gram-negative bacterial cell envelope. It is released when a cell dies and during bacterial cell division. In contrast, exotoxins are protein molecules secreted by bacteria, predominantly gram-positive, but some gram-negative bacteria produce them as well. Exotoxins are known for their specific targeting mechanisms — they attach to specific cell receptors and disrupt particular cellular functions.
Endotoxin is associated with a general systemic inflammatory response, whereas exotoxins have a much more pinpointed action. Moreover, endotoxins are stable at high temperatures and require significant heat to be inactivated, unlike most exotoxins, which are denatured at lower temperatures. Exotoxins can be catastrophic to the host even in minute quantities, exemplified by the extreme lethality of botulinum toxin.