Amino Acid Metabolism in MBBS 1

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Questions and Answers

What is the primary reason why there is no 'storage' form of protein in the body?

The body has a limited capacity to store protein

Protein is rapidly catabolized and excreted as urea

Protein is not essential for human health

Protein is needed to replace lost amino acids and allow for tissue repair (correct)

What is the recommended daily intake of protein?

50 – 70 g per day (correct)

100 – 150 g per day

70 – 100 g per day

30 – 50 g per day

What happens to surplus amino acids in a well-fed individual?

They are converted into energy

They are used to synthesize other nutrients

They are stored in the body for later use

They are rapidly catabolized and the nitrogen is excreted as urea (correct)

Which of the following amino acids can be synthesized by humans?

One of the 10 amino acids that can be synthesized from other intermediates Signup and view all the answers

What is the state of nitrogen balance when the amount of nitrogen taken in equals the amount of nitrogen excreted?

Nitrogen equilibrium Signup and view all the answers

What is the consequence of prolonged negative nitrogen balance?

Irreversible loss of essential body tissue Signup and view all the answers

In which of the following conditions is positive nitrogen balance commonly seen?

Normal growth in children Signup and view all the answers

What is the consequence of high protein intake in a well-fed individual?

Rapid catabolism of surplus amino acids and excretion of nitrogen as urea Signup and view all the answers

What is the primary role of the ubiquitin breakdown system in cellular protein regulation?

To remove damaged or old proteins Signup and view all the answers

What is the fate of most amino acids after losing their amino groups during transamination and deamination?

They are metabolized by the TCA pathway to CO2 and H2O Signup and view all the answers

Which of the following amino acids can only be degraded to acetyl CoA?

Leucine and lysine Signup and view all the answers

What is the role of cortisol in protein degradation?

It stimulates protein breakdown in muscle Signup and view all the answers

What is the process by which cells take in foreign proteins or damaged organelles?

All of the above Signup and view all the answers

What is the primary fate of the carbon skeletons of 13 amino acids during starvation?

They are converted back to glucose by the liver Signup and view all the answers

What happens to the amino groups of amino acids in the liver?

They are converted into urea for excretion. Signup and view all the answers

Which amino acid is a safe carrier of ammonia in the blood stream?

Glutamine Signup and view all the answers

What is the result of impaired conversion of NH3 to urea?

Hyperammonaemia Signup and view all the answers

Which of the following is NOT a product of nitrogen metabolism?

Glucose Signup and view all the answers

What is the primary function of the liver in nitrogen metabolism?

To degrade excess amino acids and convert them into urea Signup and view all the answers

Which amino acid can be converted into glucose?

Phenylalanine Signup and view all the answers

What is the consequence of ammonia toxicity in the brain?

Cerebral oedema, coma, and death Signup and view all the answers

What is the name of the cycle that converts ammonia into urea?

Urea cycle Signup and view all the answers

What is the average daily protein turnover in an adult?

300g-400g Signup and view all the answers

What is the primary role of amino acids in the body?

Building blocks for proteins and other molecules Signup and view all the answers

What is the term for the process of converting an amino acid into a keto acid, releasing ammonia in the process?

Deamination Signup and view all the answers

What is the significance of the classification of amino acids as essential or non-essential?

It determines the body's ability to synthesise them Signup and view all the answers

What is the term for the process of transferring an amino group from one amino acid to a keto acid, resulting in the formation of a new amino acid and a keto acid?

Transamination Signup and view all the answers

What is the term for the balance between the amount of nitrogen ingested and the amount of nitrogen excreted in the body?

Nitrogen balance Signup and view all the answers

What is the term for the process of degrading proteins into amino acids?

Protein degradation Signup and view all the answers

What is the significance of glutamate, glutamine, aspartate, and alanine in amino acid metabolism?

They are involved in the metabolism of amino acids Signup and view all the answers

Study Notes

Protein Turnover and Amino Acid Pools

Body proteins are continuously degraded to amino acids and re-synthesized, with an average turnover of 300-400g per day in an adult
Most proteins have half-lives of several days, while structural proteins like collagen may have half-lives of years
Hormones and digestive enzymes are degraded very rapidly, with half-lives of minutes
The amino acid pool consists of free amino acids in very low concentrations inside cells or in the bloodstream
Amino acids in the pool mix and exchange with other free amino acids distributed throughout the body

Nitrogen Balance

Nitrogen balance is a state where the total amount of nitrogen taken in the diet as protein is equal to the amount of nitrogen excreted from the body
Positive nitrogen balance occurs when protein synthesis exceeds the rate of breakdown, and is seen in normal growth in children, convalescence after serious illness, and pregnancy
Negative nitrogen balance occurs when protein breakdown exceeds synthesis, and is seen in starvation, serious illness, and injury

Classification of Amino Acids

There are 20 amino acids commonly found as building blocks of proteins
Humans can synthesize only 10 amino acids from other intermediates, and rely on dietary sources for the remaining essential amino acids
Essential amino acids include valine, methionine, histidine, lysine, phenylalanine, leucine, isoleucine, and threonine

Pathways of Protein Degradation

Most cellular proteins are removed by the ubiquitin breakdown system
Foreign proteins and old or damaged subcellular organelles are taken into vesicles by endocytosis or autophagocytosis, and then degraded by proteolytic enzymes in lysosomes

Transamination and Deamination

Transamination involves the transfer of the amino group of an amino acid to an acceptor molecule, such as 2-oxoglutarate, resulting in an oxo acid and glutamate
Deamination involves the release of the ammonia group as ammonia (NH3) or ammonium ions (NH4+)