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Questions and Answers
What is the primary role of deamination in amino acid metabolism?
Which of the following amino acids is considered exclusively ketogenic?
What categorizes an amino acid as glucogenic?
Which of the following is true about non-essential amino acids?
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What condition is indicated by elevated levels of AST and ALT in plasma?
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Which of the following processes is responsible for transferring the amine group from an amino acid to $eta$-ketoglutarate?
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What occurs during a negative nitrogen balance?
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Which amino acids are excluded from the transamination process?
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What is one primary function of amino acids within the body?
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During which metabolic state are amino acids primarily absorbed via a secondary active sodium-dependent transport system?
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What is the significance of glucogenic and ketogenic amino acids?
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Which amino acids primarily serve as nitrogen carriers to the liver for the urea cycle?
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What is the result of the transamination process?
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Study Notes
Protein Structure and Functions of Amino Acids
- Amino acids are the building blocks of proteins, essential for protein synthesis.
- They play roles as precursors for nitrogen-containing compounds, neurotransmitters, hormones, heme, and purine/pyrimidine bases.
- Amino acids are utilized for energy during starvation.
Protein Digestion and Absorption
- Protein digestion occurs during the fed state, with absorption facilitated by an active Na+-dependent transport system and facilitated transporters.
Nitrogen Balance
- Defined as the difference between nitrogen intake and nitrogen loss through urine, sweat, and feces.
- Healthy adults maintain a nitrogen balance of zero.
- A negative nitrogen balance indicates more nitrogen is lost than consumed, often due to inadequate protein intake, lack of essential amino acids, or physiological stress.
- A positive nitrogen balance indicates more nitrogen is ingested than excreted, necessary for growth, pregnancy, and recovery from illness.
Nitrogen Removal Processes
- Transamination and deamination are critical for protein turnover and amino acid degradation.
- Alanine and glutamine serve as major nitrogen carriers from muscle to the liver for the urea cycle.
Transamination
- Involves the transfer of an amine group from an amino acid to α-ketoglutarate, forming glutamate.
- Catalyzed by transaminases, requiring pyridoxal phosphate (vit B6).
- All amino acids undergo this process except lysine and threonine.
- Diagnostic markers such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are elevated in liver diseases and certain other conditions.
Deamination
- The process of removing nitrogen from amino acids like glutamate and asparagine, resulting in ammonia for the urea cycle.
- Deamination occurs in cells and gut bacteria.
Catabolism of Amino Acids
- Involves amino group removal and breakdown of carbon skeletons for intermediate products of metabolism.
- Glucogenic amino acids produce pyruvate or TCA cycle intermediates, important for gluconeogenesis.
- Ketogenic amino acids yield acetoacetate or acetyl CoA; leucine and lysine are exclusively ketogenic.
Classification of Amino Acids
- Glucogenic Amino Acids: Yield pyruvate or TCA cycle intermediates. Includes nonessential (e.g., alanine, asparagine) and essential amino acids (e.g., histidine, valine).
- Ketogenic Amino Acids: Yields acetoacetate or acetyl CoA. Exclusively ketogenic amino acids include leucine and lysine.
- Essential Amino Acids: Must be obtained through the diet.
- Non-Essential Amino Acids: Can be synthesized in the body from glycolytic pathway intermediates and Kreb's Cycle; amino groups are added via transamination.
Summary
- Amino acid metabolism is essential for maintaining nitrogen balance, energy production, and protein synthesis.
- Distinct metabolic pathways for glucogenic and ketogenic amino acids indicate their varied importance in energy and glucose homeostasis.
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Description
Test your knowledge on the structure and functions of amino acids, their roles in human physiology, and the intricacies of protein digestion and absorption. This quiz also covers the concept of nitrogen balance, highlighting its significance in health and nutrition.
