Amino Acid Catabolism and Urea Production
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Questions and Answers

What is the initial step in amino acid catabolism?

  • Removal of the amino group (correct)
  • Removal of the carboxylic group
  • Conversion to glucose
  • Conversion to fatty acids

Which molecule is primarily involved in nitrogen metabolism during amino acid catabolism?

  • Alanine
  • Glutamate (correct)
  • Aspartate
  • Serine

How do aquatic vertebrates primarily excrete nitrogen?

  • As ammonium ions in urine
  • As urea through kidneys
  • As uric acid through the gastrointestinal tract
  • As ammonia through diffusion or active transport (correct)

Why do many terrestrial vertebrates excrete nitrogen in the form of urea?

<p>Because urea is less toxic than ammonia (C)</p> Signup and view all the answers

What is a significant advantage of excreting nitrogen as uric acid for birds and reptiles?

<p>It allows for conservation of water (C)</p> Signup and view all the answers

What indicates liver dysfunction when elevated?

<p>ALT and AST levels (A)</p> Signup and view all the answers

Which process involves the transformation of ammonia into urea?

<p>Transdeamination (D)</p> Signup and view all the answers

What form of nitrogen is measured by BUN?

<p>Total nitrogen (C)</p> Signup and view all the answers

How is ammonia typically transported in the bloodstream?

<p>As glutamine (B)</p> Signup and view all the answers

Which enzyme is responsible for removing ammonia from glutamate?

<p>Glutamate dehydrogenase (D)</p> Signup and view all the answers

What component of liver function tests is represented as SGOT?

<p>Aspartate transaminase (B)</p> Signup and view all the answers

Which electron acceptor can be used in oxidative deamination?

<p>NAD+ (B), NADP+ (D)</p> Signup and view all the answers

In what cell organelle does oxidative deamination occur?

<p>Mitochondria (B)</p> Signup and view all the answers

Which of the following amino acids is classified as both nonessential and conditionally essential?

<p>Alanine (B)</p> Signup and view all the answers

What percentage of the body’s energy production is accounted for by the catabolism of amino acid carbon skeletons?

<p>10% (C)</p> Signup and view all the answers

Which of the following amino acids is considered essential?

<p>Lysine (D)</p> Signup and view all the answers

Which group of amino acids is primarily needed in young, growing animals or during illness?

<p>Conditionally essential amino acids (D)</p> Signup and view all the answers

Which amino acids are part of the acronym PVT TIM HALL, representing essential amino acids?

<p>Phenylalanine, Tryptophan, Methionine (C)</p> Signup and view all the answers

What is azotemia typically associated with?

<p>High levels of nitrogenous waste in blood (B)</p> Signup and view all the answers

What is the primary role of transaminations in the metabolism of amino acids?

<p>To transfer an amine group to a common metabolite (D)</p> Signup and view all the answers

Why is excess NH3 particularly harmful to the brain?

<p>It leads to glutamate accumulation causing neural toxicity (A)</p> Signup and view all the answers

Which treatment is effective in reducing ammonia levels associated with asterixis?

<p>Lactulose (A)</p> Signup and view all the answers

Which cofactor is essential for the enzymatic transamination process?

<p>Pyridoxal phosphate (A)</p> Signup and view all the answers

What happens to glutamate levels in the brain during liver failure?

<p>They build up due to impaired metabolism (C)</p> Signup and view all the answers

What is the result of the transamination of α-ketoglutarate?

<p>Generation of L-glutamate (B)</p> Signup and view all the answers

What process occurs due to excess glutamate in the brain?

<p>Formation of hepatic encephalopathy (B)</p> Signup and view all the answers

Which amino acid is specifically involved in the reaction catalyzed by alanine transaminase (ALT)?

<p>Alanine (A)</p> Signup and view all the answers

Which of the following is a temporary storage of nitrogen generated from transamination reactions?

<p>L-Glutamate (D)</p> Signup and view all the answers

What is the primary amino acid used to detoxify ammonia in the brain?

<p>Glutamine (A)</p> Signup and view all the answers

What neurological symptom is associated with ammonia toxicity?

<p>Asterixis (C)</p> Signup and view all the answers

Which enzymes are primarily monitored to assess liver function?

<p>Alanine transaminase (ALT) and aspartate transaminase (AST) (A)</p> Signup and view all the answers

The glucose-alanine cycle is most active in which type of muscle condition?

<p>Anaerobic respiration (C)</p> Signup and view all the answers

What substance is typically accepted by α-ketoglutarate during transamination?

<p>Amino group (C)</p> Signup and view all the answers

What main factor contributes to the conversion of excess glutamate into GABA?

<p>Astrocyte function (A)</p> Signup and view all the answers

What happens to L-glutamate when nitrogen is needed for amino acid biosynthesis?

<p>It donates back the amino group (C)</p> Signup and view all the answers

Which of the following correctly describes NH4+ in relation to membranes?

<p>It is in equilibrium with NH3 (A)</p> Signup and view all the answers

Which mechanism is described as using a ping-pong model in transaminations?

<p>Enzymatic transamination (A)</p> Signup and view all the answers

What is the byproduct formed when alanine is converted into pyruvate?

<p>L-Glutamate (A)</p> Signup and view all the answers

Why is free ammonia considered toxic?

<p>It disrupts cellular pH balance (B)</p> Signup and view all the answers

What type of reaction does alanine transaminase perform?

<p>Transamination (C)</p> Signup and view all the answers

What does L-glutamate regenerate during the reverse reaction of transamination?

<p>α-Ketoglutarate (D)</p> Signup and view all the answers

What is the primary role of alanine in the transport of substances to the liver?

<p>It transports amino groups and pyruvate in a non-toxic form. (A)</p> Signup and view all the answers

Which enzyme initiates the conversion of ammonia into carbamoyl phosphate in the urea cycle?

<p>Carbamoyl phosphate synthase 1 (CPS1) (B)</p> Signup and view all the answers

Which of the following is true regarding the urea cycle?

<p>The cycle requires the equivalent of 4 ATP to produce one urea. (D)</p> Signup and view all the answers

What is the function of glutamate in the context of ammonia transport?

<p>It can be converted to glutamine for ammonia transport to the liver. (B)</p> Signup and view all the answers

What byproduct is generated from the urea cycle along with the production of urea?

<p>Fumarate (D)</p> Signup and view all the answers

In the urea cycle, which enzyme facilitates the conversion of argininosuccinate into arginine?

<p>Lyase (B)</p> Signup and view all the answers

Which amino acids must be obtained through dietary sources?

<p>Essential amino acids (B)</p> Signup and view all the answers

What happens to ammonia after it is generated in mitochondria?

<p>It enters the urea cycle. (B)</p> Signup and view all the answers

Flashcards

Amino Group Removal

The process of removing amino groups from amino acids during catabolism.

Transamination

Transfer of an amino group from an amino acid to a keto acid, creating a new amino acid and keto acid.

Aminotransferases

Enzymes that catalyze transamination reactions.

Pyridoxal Phosphate (PLP)

A coenzyme essential for transaminase function and a key part of vitamin B6 metabolism.

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α-ketoglutarate

A keto acid that accepts amino groups in transamination reactions.

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L-glutamate

An amino acid that acts as a temporary storage site for nitrogen, obtained from amino group transfer.

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Alanine Transaminase (ALT)

An enzyme that catalyzes the transfer of an amino group from alanine to α-ketoglutarate, producing pyruvate.

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Liver Function Tests

Blood tests that measure levels of liver enzymes, including ALT and AST, used to assess liver health.

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Transaminase Ping-Pong

A catalytic mechanism of aminotransferases. The enzyme reacts and regenerates its original form for repetitive catalytic cycles.

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Liver Enzymes

Components of liver function tests (LFTs), elevated levels indicate liver dysfunction like cirrhosis or hepatitis.

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ALT and AST

Liver enzymes; elevated levels signal potential liver problems.

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SGOT/SGPT

Alternative names for liver enzymes (AST/ALT), found in lab results.

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Transaminases (AST/GOT)

Essential enzymes catalyzing amino acid and alpha-keto acid interconversion in liver.

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Ammonia Transport

Ammonia, a toxic byproduct, is transported via glutamine to the liver for processing.

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Glutamine

A molecule that carries ammonia from tissues to the liver for urea production.

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Glutamate Dehydrogenase

Enzyme that further removes ammonia from glutamate in the liver's mitochondria.

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Oxidative Deamination

Process that removes ammonia from glutamate within liver mitochondria.

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Urea

The final form of ammonia excretion in the body.

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Transdeamination

Combination of transamination and oxidative deamination to remove ammonia completely.

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Blood Urea Nitrogen (BUN)

A lab test measuring the amount of urea nitrogen in blood, indicating kidney or liver health.

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Ammonia toxicity

Excess ammonia, often due to liver failure, is harmful to the brain, causing hyperammonemia, glutamate buildup, hepatic encephalopathy, asterixis (flapping tremor), and coma.

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Asterixis

A flapping tremor, a sign of liver failure and ammonia toxicity.

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Glutamate

An excitatory neurotransmitter; excess buildup due to liver failure can be harmful.

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Glutamine

An amino acid crucial for ammonia detoxification in the brain. (Converted from glutamate)

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Ammonia detoxification

The process of converting ammonia to less toxic forms, like urea in the liver, or glutamine in the brain.

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Urea cycle

Metabolic pathway in the liver that converts ammonia to urea for excretion.

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Hyperammonemia

High levels of ammonia in the blood.

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Lactulose

A disaccharide used to treat asterixis, binding ammonia and promoting its excretion.

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Hepatic encephalopathy

Brain dysfunction due to liver failure and ammonia accumulation.

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Pyruvate Conversion

Part of pyruvate from glycolysis is converted to lactate, while another part is converted to alanine for transport to the liver.

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Alanine Transport

Alanine carries amino groups and pyruvate to the liver in a non-toxic form.

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Alanine to Pyruvate

The liver reconverts alanine to pyruvate for gluconeogenesis and excretes ammonia as urea.

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Glutamine Transport

Glutamate can be converted to glutamine in muscle to transport ammonia to the liver.

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Carbamoyl Phosphate

Ammonia is initially converted to carbamoyl phosphate in the urea cycle.

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Urea Cycle Enzymes

Enzymes like CPS1, OTC, Synthetase, Lyase, and Arginase work sequentially to convert ammonia to urea.

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Urea Cycle ATP

Production of urea requires the equivalent of four ATP molecules.

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Essential Amino Acids

Essential amino acids must be obtained from the diet.

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Amino Acid Catabolism

The breakdown of amino acids for energy production or other uses.

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NH4+

Ammonium ion; the result of removing the amino group from amino acids.

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α-keto acids

The carbon skeletons of amino acids remaining after the amino group is removed.

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Central Metabolism

Metabolic pathways like glycolysis and the citric acid cycle used to generate energy.

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Liver's role in Nitrogen Metabolism

The liver processes excess amino acids, converting ammonia to less toxic forms like urea or uric acid.

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Urea

A less toxic form of nitrogenous waste, produced in the liver, and excreted by many terrestrial vertebrates and sharks.

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Uric Acid

A nitrogenous waste product, largely insoluble, often excreted as a paste by birds and reptiles.

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Glutamine

A key amino acid for nitrogen transport and metabolism.

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Glutamate

A key amino acid involved in nitrogen metabolism and conversion to α-ketoglutarate.

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Alanine

An amino acid converted to pyruvate as part of nitrogen metabolism.

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Aspartate

An amino acid converted to oxaloacetate for nitrogen metabolism.

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Nitrogenous waste

A byproduct of metabolism that contains nitrogen.

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Ammonia Excretion

Many aquatic animals release ammonia into their environment.

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Plant Nitrogen Conservation

Plants often retain most nitrogen compounds.

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Essential Amino Acids

Amino acids that the body cannot produce and must be obtained from food.

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Nonessential Amino Acids

Amino acids that the body can produce from other compounds.

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Conditionally Essential Amino Acids

Amino acids that are not usually essential but become so under specific conditions like illness or growth.

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Amino Acid Degradation

Breaking down amino acids to release energy. This is a part of catabolism.

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Energy Production

Amino acid breakdown contributes 10% of the body’s energy needs.

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Study Notes

Amino Acid Catabolism and Urea Production

  • Amino acid catabolism occurs during normal protein degradation/synthesis (protein turnover) within cells, recycling amino acids into new proteins. Excess amino acids are also catabolized.
  • Catabolism also happens when animals rely solely on meat (carnivores) or when the diet provides more amino acids than the body needs for protein synthesis.
  • Starvation and uncontrolled diabetes mellitus also cause amino acid catabolism, as carbohydrates are unavailable.

Dietary Protein Digestion

  • Food triggers gastric mucosa cells to release gastrin, stimulating HCl secretion by parietal cells and pepsinogen secretion by chief cells.
  • Pepsinogen is converted into pepsin at low pH (1.5-2).
  • Pepsin breaks down proteins into peptides in the stomach.
  • Trypsin and chymotrypsin further break down proteins and peptides into smaller peptides in the small intestine.
  • Aminopeptidase and carboxypeptidases A and B in the small intestine break down peptides into amino acids which are absorbed.

Amino Acid Catabolism Pathways

  • Absorbed amino acids are used for making new proteins or for energy.
  • Amino acids are first converted to ammonia (NH4+) and a-keto acids (carbon skeletons), which are then further catabolized.
  • Excess amino acids are sent to the liver for catabolism, transporting ammonia.
  • Ammonia is reused or excreted as urea or uric acid.
  • Glutamate, glutamine, alanine and aspartate are crucial for nitrogen metabolism. They are easily converted into TCA intermediates (a-ketoglutarate, pyruvate, oxaloacetate).

Ammonia Handling and Transport

  • Free ammonia is toxic and cannot be released directly into the bloodstream.
  • Ammonia is recycled by converting it into glutamine.
  • Excess ammonia is transported to the liver (and to a lesser degree to specialized cells in small intestine and kidneys) via glutamine.
  • Glutamine is converted into urea for excretion.

Enzymatic Transamination

  • Transamination: transfer of an amino group from an amino acid to a-ketoglutarate, producing glutamate.
  • Aminotransferases (also called transaminases) catalyze this reaction.
  • Pyridoxal phosphate (vitamin B6) is a cofactor required for these enzymes.
  • Glutamate acts as a temporary storage of nitrogen.

Urea Cycle

  • Ammonia is first converted into carbamoyl phosphate, by CPS1 in mitochondria.
  • The urea cycle is a series of reactions converting ammonia into urea.
  • Key enzymes in the urea cycle include carbamoyl-phosphate synthetase I (CPS1), ornithine transcarbamoylase (OTC), ornithine-transcarbamoylase, argininosuccinate synthetase, argininosuccinase, and arginase.

Essential vs. Nonessential Amino Acids

  • Essential amino acids must be obtained from the diet, while nonessential amino acids can be synthesized by the body.
  • Some amino acids are conditionally essential under specific conditions, like growth, illness or specific metabolic needs (example: arginine).

Amino Acid Degradation Pathways

  • Catabolism pathways for various amino acids that eventually feed into the central metabolic pathways like the Krebs cycle
  • There are also specific pathways for some amino acids that can branch off into different pathways.
  • Some amino acids have both glucogenic and ketogenic pathways, meaning their carbon skeletons can be used to make glucose or ketone bodies.

Ammonia Toxicity

  • Ammonia is toxic to the brain.
  • High levels of ammonia can lead to hyperammonemia, causing neurological problems (hepatic encephalopathy), asterixis (liver flap), and coma.
  • Treatment strategies for high ammonia levels involve managing the underlying cause (like liver failure), and possibly using lactulose to remove ammonia through the intestines.

Clinical Aspects of Amino Acid Metabolism

  • Liver enzyme tests (ALT and AST) are used to assess liver function and diagnose liver disease or damage.
  • Genetic disorders affecting amino acid catabolism can cause a variety of symptoms (e.g., inborn errors of metabolism).
  • These disorders often have specific characteristic features, which can be used for diagnosis and treatment options.

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Amino Acid Catabolism and Urea Production PDF

Description

This quiz explores the processes of amino acid catabolism and urea production, including their significance during normal metabolism and under specific dietary conditions such as carnivory and starvation. It also covers the digestion of dietary proteins in the stomach and small intestine, detailing enzyme functions and pH levels involved. Test your knowledge on these vital biochemical processes!

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