Detoxification

• one important role of the liver is detoxifying substances that may cause harm. Some compounds, such as hydrogen peroxide, are produced in the body. Other toxic compounds may be consumed as part of our diet, health, or recreational reasons- e.g. medicine and/or recreational drugs.
• Toxins can be rendered harmless via oxidation, reduction, methylation and or combining with another molecules. Liver cells contain many enzymes that render toxic molecules less toxic.
• What is the significance of catalse in the liver?

  Catalse converts hydrogen peroxide to oxygen and water. Catalase has a particularly high turnover number (the number of molecules of hydrogen peroxide that one molecule of catalase can render harmless in one second) of five million.
• What is the significance of cytochrome P450 in the liver?

  P450 is a group of enzymes used to breakdown drugs including cocaine and various medicinal drugs. The cytochrome are also used in other metabolic reactions such as electron transport in respiration. Their role in metabolising drugs can interfere with other metabolic roles and cause the unwanted side effects of some medicinal drugs.
• Alcohol, aka ethanol, is a drug that depresses nerve activity. Alcohol contains chemical potential energy which can be used in respiration
• Alcohol is broken down by hepatocytes by the action of the enzyme alcohol dehydrogenase. The resulting compound is ethanal. The final compound produced is ethanoate, acetate. This acetate is combined with a co-enzyme A to form acetyl coenzyme A which enters the process of aerobic respiration. The hydrogen atoms released from alcohol are combined with another coenzyme called NAD to form reduced NAD.
• The co-enzyme NAD is also required to oxidize and break down fatty acids for use in respiration. If the liver has to detoxify too much alcohol. it uses up stores of NAD and has insufficient left to deal with the fatty acids. These fatty acids are then converted back to lipids and stored as fat in the hepatocytes which causes the liver to become enlarged. This is also known as having a fatty liver, leading to alcohol-related hepatitis or cirrhosis.
• Why cant excess amino acids be stored?

  They are toxic due to the amino groups.
• the process to get from an amino acid to urea is what?

  For an amino acid to be converted into ammonia and a keto acid, it undergoes deamination. For the ammonia and keto acid to become urea it goes through the ornithine cycle
• Describe the process of deamination.

  deamination removes the amino group and produces ammonia. Ammonia is very soluble and highly toxic thus it cannot be allowed to accumulate. Keto acid is also produced, this is an organic compound which can be directly used in respiration
• what is the first step of the ornithine cycle?

  Ammonia (N H 3) is produced from the deamination of amino acids.
• What is the second stage of the ornithine cycle?

  In the mitochondria, ornithine reacts with carbamoyl phosphate (formed from ammonia and carbon dioxide).
• What is the third stage of the ornithine cycle?

  There is a reaction to form citrulline, which exits the mitochondria into the cytosol.
• What is the fourth stage in the ornithine cycle?

  Citrulline reacts with aspartate to form arginine in the cytosol.
• What is the fifth stage in the ornithine cycle?

  Arginine is broken down by the enzyme arginase, releasing urea, which is excreted in urine, and regenerating ornithine to continue the cycle.