Question

Assignment Score: 0% Resources Hint Check Answer Question 3 of 18 > The doctor asks you, "If botulinum toxin was present and cleaved the SNAP/SNARE complex, would the Ach concentration in the synaptic cleft be higher or lower than normal, and why would this be?" The concentration of Ach would be in the synaptic cleft, because impaired vesicle lower fusion reduces endocytosis of Ach by the postsynaptic cell. formation reduces endocytosis of Ach by the postsynaptic cell. fusion reduces crocytosis of Ach formation within the presynaptic cell reduces exocytosis of Ach. acer ģ nik

Answer 1

Ans) Botulinum toxin is secreted by Clostridium botulinum.It is a neurotoxin and thus inhibits the release of neurotransmitter i.e acetylcholine in the synaptic cleft thereby affecting the nerve impulse transmission (From 1 cell to another) and ultimately causing paralysis.Thus, the concentration of Acetylcholine will be "lower" (as asked in the question). Apart from being a neurotoxin, it also has a proteolytic activity and cleaves SNAP/SNARE complex.

Now lets solve the question,

Vesicle fusion requires V-SNARE (VAMP,Syntaxin) to interact with T-SNARE (SNAP-25) to dock the vesicle with the target membrane. In the normal case, the loaded vesicles with the neurotransmitter will dock at the synaptic site with the help of SNAP/SNARE complex,neurotransmitter will be released in the synaptic cleft by exocytosis of loaded vesicle and then the clathrin coated vesicle will be pinched off by dynamin protein by undergoing GTP hydrolysis.

In the case of botulinum toxin,it will cleave SNAP/SNARE complex thereby affecting the fusion or docking and thus reducing or inhibiting the release of acetylcholine in the synaptic cleft.

$\therefore$ The answer is "The concentration of Ach would be lower in the synaptic cleft,because impaired vesicle fusion reduces exocytosis of Ach".

The other option would be incorrect because there is no endocytosis taking place in this process and the cleavage of SNAP/SNARE complex will impair the vesicular fusion or docking process and not the vesicle formation (vesicles will be formed normally,only the fusion will be impaired).