1) Botulinum toxin (BT) is not only the basis of Botox treatments but is also us
ID: 5896 • Letter: 1
Question
1) Botulinum toxin (BT) is not only the basis of Botox treatments but is also used in many medical applications. Recent studies have shown that after this chemical is injected into synapses of facial neurons, it appears in the brain. How would you hypothesize that BT travels to the brain in these circumstances? 2) Given the simple mechanism shown in the figure, explain how diarrhea may result from the alteration in the pathway by the E. coli stimulating adenlylate cyclase [Hint: Keep in mind that diarrhea is really just an excess of water being moved out of the cell into the lumen, and consider what may lead to that water imbalance.Explanation / Answer
1. The botulinum toxin which is injectes into synapses of facial neurons can easily enter the brain. A synapse is a junction between two axons. So this toxin enters the axon by endocytosis. It then travels up the axon to the neuron and then into the brain.2. The microbe E.coli can act in a similar way as the cholera toxin. The cholera toxin uses the signal transduction pathway to wreak havoc.A protein called the G protein is present at the plasma membrane. This protein has 3 subunits. The toxin ribosylates the subunit of this protein. By adding a ribosyl group it activates this subunit.It activates this subunit permanently. once the subunit is activated, it activates the enzyme adenylate cyclase. This enzyme then activates the secondary messenger cAMP. This secondary messenger cAMP then activates the protein kinase enzyme. The activated protein kinase then phosphorylates the following proteins of the cascade. The final result is the secretion of water and the different ions like Na+ and Cl- into the lumen of the intestine. This excess water and electrolytes go out in the form of diarrhoea. All the water in the cell comes out. The electrolyte balance is lost with the loss of both Na+ and Cl-
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