Discuss how protein/amino acid metabolisand energy metabolism are interlinked

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Question:- Discuss how protein/amino acid metabolisand energy metabolism are interlinked.


Metabolism is defined as the sequence of chemical reactions occurs in the living organisms to maintain life. It includes anabolism and catabolism.

Proteins are building blocks of the muscles and provide constituent materials to the body. Protein metabolism is the process which results in formation of proteins from the amino acids. It includes five phenomenons' that are amino acid synthesis, transcription, translation, post translational modifications, and protein folding.

The nutrients which provide energy are basically lipids and carbohydrates. Energy metabolism refers to the process of producing energy in the form of ATP, through the nutrients. Metabolism of energy consists of connected pathways which can function in the absence as well as presence of oxygen. In the presence of oxygen (aerobic), one glucose molecule converts to approximately 30 to 32 ATP molecules. In the absence of oxygen (anaerobic), the fermentation is less efficient than the presence of oxygen.

Proteins are also a source of energy in some cases. So, in case of starvation or when energy intake is inadequate, some consumed proteins are used as an energy source. On the other hand, proteins in body do not have a form for energy storeroom, such as triglycerides (triacylglycerol) for lipids and glycogen for carbohydrates. Consequently, amino acids (gained mainly by partial degradation of muscle proteins can be used for energy).

Proteins may hydrolyzed by many kind of enzymes. Many time, amino acid are recycled for the production of new proteins, and sometimes for glucose catabolism. Every amino acid has its own amino group, which can be eliminated before the entry into pathways. The amino group leads to conversion into ammonia. The liver produces urea from 2 ammonia molecules and one carbon dioxide molecule. So, nitrogen is the waste product in the metabolism of amino acids, which can excreted through urine from the body.

The breakdown and production of lipids, carbohydrates and proteins are connected with the pathways for catabolism of glucose. The simplest form of carbohydrates are galactose, glycogen, fructose, and pentose. These all are catabolized through glycolysis. The amino acids connects with the catabolism of glucose through acetyl CoA, pyruvate, and elements of citric acid cycle. The synthesis of carbohydrate begins with the acetyl group, and the elements of triglycerides which comes from the glycerol-3-phosphate from the acetyl groups generated in the mitochondria from pyruvate and through the process of glycolysis.

So, we can say that the metabolic pathway is connected with pathways of glycolysis and citric acid cycles, but they may undergo different pathways at some points. 

Question 2:- 

Case study: A 14-year-old European male was admitted to A & E with the following symptoms; a history of nausea and vomiting and an altered mental status. A blood profile of the patient’s renal function and serum electrolytes was within normal range. The patient was given antiemetics and intravenous fluid treatment. However, having not improved the patient was found to have a blood ammonia level of 280mmol/L (reference interval of < 50mmol/L). Blood analysis identified loss of a specific enzyme and confirmed a diagnosis of Citrullinemia (Type I).

Demonstrate your understanding of the urea cycle by discussing what citrullinemia is, including the specific enzyme that is defective and highlighting the key differences between type I and type II. Finally, what effect does this rise in ammonia levels have on the patient's survival outcome and why?


Question 2- Part b- case study

The urea cycle in the body is primarily involved with the clearance of ammonia in the form of urea through a cyclical process called as ornithine cycle. There are many steps involved in this process and each step is directed by a specific enzyme to break down the metabolic products. In this case, the lack of or a deficiency of the enzymes results in the urea cycle disorders. Prominently there are two types of disorders Citrullinemia type 1 and type 2. While type 1 is typically observed in the neonates or a relatively milder form in the later years. This is due to the deficiency of the enzyme argininosuccinate synthetase. This may occur due to the mutations in the ASS1 gene.  The most common symptoms associated with this disorder is vomiting, encephalopathy, hyperammonemia, intracranial pressure and accumulation of toxic products such as glutamine (Quinonez & Thoene, 2016). The citrullinemia type 2 is usually observed in the adults or has a late onset. The most common symptoms in this case also are very similar to the previous case and also include hepatomegaly, hypoglycemia and fibrosis in the liver. In this case the deficiency of citrin a transporter protein i.e., aspartate in the surface of the mitochondria. The hepatic glycosis is negatively affected by this deficiency (Hayasaka & Numakura, 2018)

In the cells, there are different ammonia detoxification systems, of which primarily it is ureagenesis i.e. the production of urea and the other glutamine synthesis. The glutamine synthesis system hunts for the ammonia molecules in the cells and maintains the low ammonia concentrations in the blood. The glutamine synthase is involved in the conversion of the glutamine from glutamate in the presence of ammonia. An impairement in this function of the enzyme leads to the accumulation of ammonia as is seen in the current case of the 14-year old. (Hayasaka & Numakura, 2018)

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