What is Acetaminophen toxicity and what are the lethal consequences of an overdose?

Acetaminophen is one of the most commonly used oral analgesic (pain-killer), also known as paracetamol and Tylenol. Overdose would mean exceeding the 4000 mg daily recommended dose and lethal dose ranges from 10-15 g in adults. Toxicity would manifest in 4 phases of clinical symptoms, with the risk of liver failure. Oxidation of paracetamol produces a toxic product N-acetyl-p-benzoquinone imine (NAPQI) via the glucuronide pathway. Glutathione inactivates NAPQI in a normal pathway. On overdose the altered pathway produces NAPQI in excess. Liver reserves of glutathione (cellular reducing agent) are depleted by conjugation with the excess NAPQI. This results in oxidative stress, mitochondrial damage, and necrosis of hepatocytes.

A catalyst X is employed in a biochemical reaction, how are the following affected in the course of the reaction: a) Initial and Final Energy levels b) Reaction rate c) Catalyst

Biological catalysts which are mostly enzymes alter many biochemical reactions such as photosynthesis, respiration etc. The catalysis does not alter the state of the energy of the substrates or products. Enzymes (proteinaceous or RNA based ribozymes) increase the reaction rates by million folds, whereas inorganic catalysts (metal salts) increase the reaction rate up to 100 folds. The biocatalysts alter the reaction rate for a thermodynamically feasible reversible reaction without undergoing any irreversible chemical damage/change.

Why does one often yawn while exercising?

There are two possible explanations for this phenomenon : 1. Our bodies naturally warm up when we work out, the temperatures rise and as a mechanism to cool the body by bringing in the fresh air, the brain stimulates a yawn. 2.With the metabolism speeding up coupled with an increased blood supply towards the exercising muscles, there is a possible temporary lack of blood flow to the brain. To make up for the oxygen deficit there's a yawn. To keep the body alert the brain signals it to draw in fresh air.