Fill in the Blanks. The diphtheria exotoxin is an a-b toxin that __________. view available hint(s) the diphtheria exotoxin is an a-b toxin that __________. causes host cell lysis is encoded for by genes in the chromosome of corynebacterium diphtheriae cells is found in all corynebacterium diphtheriae cells is found only in corynebacterium diphtheriae cells that have been infected with lysogenic bacteriophage β

The diphtheria exotoxin is an A-B toxin that is found only in Corynebacterium diphtheriae cells that have been infected with lysogenic bacteriophage β.

Extra: Diphtheria is a disease caused by the bacterium Corynebacterium diphtheriae. However, not all strains of this bacterium cause diphtheria. In order for the bacterium to be capable of causing the disease, the bacterium must be infected by a certain type of virus called a bacteriophage. Specifically, it's the lysogenic bacteriophage β (beta) which carries the gene for the diphtheria toxin. When the bacteriophage integrates its genetic material into the bacterial chromosome (a process known as lysogeny), the bacterial cells gain the ability to produce the diphtheria toxin. This toxin is an example of an A-B toxin, which means it has two components: the A part (active component) that is responsible for the toxic effect, and the B part (binding component) that binds to the surface of host cells and enables the entry of the A part into the cell. The A component of this toxin blocks protein synthesis in the host cell, leading to cell death. This process can cause severe symptoms in humans, which is why diphtheria used to be a major cause of illness and mortality before vaccines were introduced.