Lippincott's Biochemistry Chapter 19 - Amino Acids (Nitrogen Disposal)
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Questions and Answers

What is the primary mechanism through which nitrogen is disposed of from the body?

  • Formation of urea (correct)
  • Synthesis of amino acids
  • Conversion to creatinine
  • Release as free ammonia

Which of the following conditions is most likely to cause hyperammonemia?

  • Increased energy expenditure
  • High levels of glucose consumption
  • Deficiency in urea cycle enzymes (correct)
  • Excessive protein intake

What role does glutamine play in nitrogen metabolism?

  • It is a storage form of amino acids.
  • It is a precursor for glucose synthesis.
  • It directly converts ammonia into urea.
  • It carries ammonia to the liver for excretion. (correct)

Which of the following symptoms is commonly associated with ammonia intoxication?

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

Which strategy is primarily utilized for detoxifying ammonia in the body?

<p>Synthesis of urea (C)</p> Signup and view all the answers

What mechanism is primarily responsible for keeping blood ammonia levels low in the liver?

<p>Glutaminase and GDH in peri-portal hepatocytes (D)</p> Signup and view all the answers

Which condition can lead to hyperammonemia?

<p>Genetic defects in the urea cycle (C)</p> Signup and view all the answers

What is the role of glutamine synthetase in ammonia detoxification?

<p>It acts as an ammonia scavenger. (D)</p> Signup and view all the answers

Which of the following is NOT a symptom of ammonia intoxication?

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

When liver function is compromised, what level of blood ammonia is considered a medical emergency?

<p>Above 1,000 µmol/L (C)</p> Signup and view all the answers

What immediate effect does elevated ammonia concentrations have on the central nervous system?

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

Which substance combines with glutamine to help detoxify ammonia in the body?

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

What is the normal range for blood ammonia levels?

<p>5-35 µmol/L (B)</p> Signup and view all the answers

Which component is essential for activating CPS I in the urea cycle?

<p>N-acetylglutamate (B)</p> Signup and view all the answers

What is the primary consequence of hyperammonemia on the central nervous system?

<p>Toxicity leading to potential damage (B)</p> Signup and view all the answers

How is ammonia primarily transported from peripheral tissues to the liver?

<p>Through glutamate and glutamine (A)</p> Signup and view all the answers

Which factor does NOT contribute to the regulation of ammonia levels in the body?

<p>Dietary fat intake (D)</p> Signup and view all the answers

What is the primary metabolic pathway that produces ammonia from amino acids?

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

Which clinical symptom is commonly associated with ammonia intoxication?

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

What strategy is primarily employed for ammonia detoxification in the liver?

<p>Formation of urea (C)</p> Signup and view all the answers

What role does arginine serve in relation to N-acetylglutamate synthase?

<p>Activator of N-acetylglutamate synthase (C)</p> Signup and view all the answers

In which condition is an increased production of ammonia most likely to occur?

<p>High protein diet (C)</p> Signup and view all the answers

Which of the following is NOT a function of glutamate in ammonia metabolism?

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

What is the primary mechanism for ammonia removal in the central nervous system?

<p>Formation of glutamine from glutamate and ammonia (B)</p> Signup and view all the answers

Which process primarily disposes of ammonia produced in the liver?

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

What condition can arise from a buildup of ammonia in the blood?

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

Which amino acid is typically released by muscle to transport nitrogen instead of ammonia?

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

What is a key reason for the low levels of ammonia in the blood?

<p>Efficient removal by the liver (D)</p> Signup and view all the answers

What clinical symptoms can result from ammonia intoxication?

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

Which tissue is primarily responsible for the synthesis of glutamine from glutamate and ammonia?

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

What form of nitrogen do skeletal muscle and other tissues typically release?

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

Which of the following best describes the role of glutamine in the body?

<p>A transport form of ammonia and a source of nitrogen (B)</p> Signup and view all the answers

How does the body primarily form ammonia from dietary amines?

<p>By the action of monoamine oxidase (A)</p> Signup and view all the answers

What is the primary mechanism by which the body disposes of nitrogen from amino acids?

<p>Synthesis of urea in the liver (C)</p> Signup and view all the answers

Which condition is NOT a major cause of hyperammonemia?

<p>Chronic kidney disease (A)</p> Signup and view all the answers

In the context of amino acid metabolism, what role does glutamine play?

<p>Transports nitrogen safely to the liver (A)</p> Signup and view all the answers

Hyperammonemia can lead to neurologic effects primarily due to damage in which part of the body?

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

What is the main consequence of ammonia not being detoxified effectively in the body?

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

Which enzyme deficiency is associated with congenital hyperammonemia?

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

What is the primary use of free ammonia in the human body?

<p>Conversion to urea for excretion (A)</p> Signup and view all the answers

Alanine functions primarily in what capacity regarding nitrogen transport?

<p>To transport nitrogen to the liver for disposal (C)</p> Signup and view all the answers

Which of the following describes the main pathway for removing amino groups from amino acids?

<p>Deamination to form a-keto acids (A)</p> Signup and view all the answers

Which clinical condition is primarily characterized by an accumulation of ammonia in the bloodstream?

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

What is the immediate consequence of argininosuccinate cleavage in the urea cycle?

<p>It yields arginine and fumarate. (D)</p> Signup and view all the answers

Which statement accurately describes the transport and fate of urea after its synthesis?

<p>Urea diffuses into the kidneys to be filtered and excreted. (D)</p> Signup and view all the answers

What is the role of malate in the urea cycle and associated metabolic pathways?

<p>Malate links to the TCA cycle and can be used for gluconeogenesis. (B)</p> Signup and view all the answers

Which enzyme exclusively cleaves arginine to yield ornithine and urea in the urea cycle?

<p>Arginase-1 (C)</p> Signup and view all the answers

What occurs to urea in the intestine after being transported from the blood?

<p>Urea is cleaved by bacteria into carbon dioxide and ammonia. (B)</p> Signup and view all the answers

What occurs to ornithine in the metabolic process described?

<p>It is transformed into L-arginine. (D)</p> Signup and view all the answers

What is the primary role of fumarase within this metabolic pathway?

<p>To convert malate to fumarate. (D)</p> Signup and view all the answers

What is synthesized from citrulline in the described process?

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

What distinguishes short-lived proteins from long-lived proteins regarding their half-lives?

<p>Short-lived proteins typically have half-lives of minutes to hours. (C)</p> Signup and view all the answers

In the mitochondria, which reaction involving ammonia is indicated?

<p>Conversion to L-ornithine. (C)</p> Signup and view all the answers

Which enzyme system is primarily responsible for the selective degradation of damaged proteins?

<p>Ubiquitin-proteasome system (A)</p> Signup and view all the answers

Which amino acid is primarily involved in the transport of nitrogen as described in the process?

<p>L-arginine (B)</p> Signup and view all the answers

What is the primary role of ubiquitin in the ubiquitin-proteasome system?

<p>It tags proteins for degradation. (B)</p> Signup and view all the answers

What is the effect of increased ammonium ion concentration in the mitochondria?

<p>Inhibition of urea synthesis. (A)</p> Signup and view all the answers

How do lysosomes contribute to protein degradation?

<p>By nonselectively degrading proteins through hydrolases. (D)</p> Signup and view all the answers

Which type of proteins typically have half-lives measured in months or years?

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

What is required for the regeneration of fumurate in this pathway?

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

Which product is generated when ammonia combines with other components in the mitochondrial matrix?

<p>L-ornithine (B)</p> Signup and view all the answers

What happens to nitrogen from amino acid degradation in the body?

<p>It is released as ammonia and then converted to urea. (C)</p> Signup and view all the answers

What characterizes proteins targeted for degradation by the ATP-dependent ubiquitin-proteasome system?

<p>They have been incorrectly synthesized. (A)</p> Signup and view all the answers

What structural form does L-arginine take within the cellular process described?

<p>A substrate for biosynthesis. (A)</p> Signup and view all the answers

What is the primary significance of citrulline in cellular metabolism as illustrated?

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

What is the main role of E3 ligase in the ubiquitin-proteasome pathway?

<p>Identifies degradation signals on target proteins (A)</p> Signup and view all the answers

Which of the following best describes the process of ubiquitination?

<p>It requires ATP hydrolysis for the transfer of ubiquitin (B)</p> Signup and view all the answers

What happens to proteins that are tagged with polyubiquitin chains?

<p>They are recognized and unfolded by the proteasome (D)</p> Signup and view all the answers

What characterizes the proteasome's role in protein degradation?

<p>It consists of multiple subunits forming a catalytic core (A)</p> Signup and view all the answers

Which of the following statements about ubiquitin is accurate?

<p>It can be recycled after protein degradation (D)</p> Signup and view all the answers

How do degradation signals influence protein half-lives?

<p>They provide specific cues for selective degradation (A)</p> Signup and view all the answers

Which type of enzymes has the highest diversity in the ubiquitin-proteasome system?

<p>E3 enzymes (D)</p> Signup and view all the answers

What is the primary function of ATP in the ubiquitin-proteasome pathway?

<p>To provide energy for the tagging and degradation processes (B)</p> Signup and view all the answers

In the context of protein degradation, what occurs after a protein is cut into fragments by the proteasome?

<p>The fragments are further degraded by cytosolic proteases (B)</p> Signup and view all the answers

Which of the following substances contributes to the formation of urea by providing a nitrogen atom?

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

What role does bicarbonate play in urea synthesis?

<p>It provides carbon for urea. (A)</p> Signup and view all the answers

In the context of urea formation, which biological process is most directly associated with free ammonia?

<p>It provides nitrogen for urea synthesis. (B)</p> Signup and view all the answers

Which compounds react to produce urea during the urea cycle?

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

Which of the following processes occurs in the liver as part of nitrogen metabolism?

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

How is the nitrogen in urea ultimately derived from aspartate?

<p>By deamination of the amino group. (B)</p> Signup and view all the answers

Which molecule is primarily formed as a byproduct when ammonia is detoxified in the liver?

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

Which enzyme plays a crucial role in the initial step of the urea cycle?

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

What is the source of the ammonia that is involved in the formation of urea?

<p>Deamination of amino acids (A)</p> Signup and view all the answers

During the urea synthesis process, which role does aspartate primarily serve?

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

Match the following processes with their corresponding descriptions:

<p>Transamination = The process of transferring an amino group to a keto acid Oxidative deamination = The removal of an amino group to produce ammonia Urea cycle = The metabolic pathway for converting ammonia to urea Glucose metabolism = Utilization of carbon skeletons from amino acids for energy</p> Signup and view all the answers

Match the following nitrogen-containing products with their primary source:

<p>Urea = Excess nitrogen from amino acid catabolism Creatinine = Byproduct of muscle metabolism Ammonia = Product of amino acid degradation Glutamine = Transport form of nitrogen in the bloodstream</p> Signup and view all the answers

Match the following amino acids with their roles in nitrogen metabolism:

<p>Alanine = Transports nitrogen to the liver Arginine = Precursor in urea cycle reactions Glutamate = Amino donor in transamination Ornithine = Intermediate in the urea cycle</p> Signup and view all the answers

Match the following terms with their meanings:

<p>Nitrogen catabolism = Breakdown of amino acids for energy and waste Ammonia detoxification = Conversion of ammonia into less toxic substances Keto acids = Carbon skeletons remaining after amino group removal Amino acid synthesis = Formation of amino acids from simpler compounds</p> Signup and view all the answers

Match the following stages of amino acid catabolism with their processes:

<p>Phase I = Removal of amino groups Phase II = Conversion to energy-producing intermediates Transamination = Transfer of amino groups to create new amino acids Deamination = Direct removal of amino groups yielding ammonia</p> Signup and view all the answers

Match the sources contributing to the amino acid pool with their descriptions:

<p>Degradation of endogenous proteins = Amino acids released from body proteins Exogenous dietary protein = Amino acids obtained from food Synthesis of nonessential amino acids = Amino acids created from simple metabolic intermediates Consumption for nitrogen-containing molecules = Amino acids utilized as building blocks for small molecules</p> Signup and view all the answers

Match the processes involved in amino acid pool depletion:

<p>Synthesis of body protein = Amino acids used to create body proteins Conversion to glucose = Amino acids transformed into glucose for energy Conversion to ketone bodies = Amino acids used to produce ketones Oxidation = Amino acids broken down for energy release</p> Signup and view all the answers

Match the terms related to protein turnover with their definitions:

<p>Protein synthesis = The process of creating new proteins Protein degradation = The breakdown of proteins into amino acids Protein turnover = The balance between protein synthesis and degradation Total protein maintenance = Keeping protein levels constant in the body</p> Signup and view all the answers

Match the components involved in nitrogen metabolism:

<p>Ammonia (NH3) = A toxic nitrogenous waste product Urea = A safer nitrogen waste excreted in urine Glucose = A primary energy source from amino acids Fatty acids = Energy storage molecules derived from amino acids</p> Signup and view all the answers

Match the dietary protein source with its classification:

<p>Animal protein = Complete protein containing all essential amino acids Plant protein = Incomplete protein lacking one or more essential amino acids High-protein diet = Diet significantly above average protein intake Common U.S. diet = Diet with typical protein consumption around 100 g/day</p> Signup and view all the answers

Flashcards

Ammonia Metabolism

The process by which the body removes ammonia, a toxic byproduct of protein breakdown.

Urea Cycle

A series of biochemical reactions in the liver that convert ammonia into urea, a less toxic compound, for excretion.

Hyperammonemia

A medical condition characterized by excessively high levels of ammonia in the blood.

Blood Ammonia Levels

Normal blood ammonia levels are typically 5-35 µmol/L.

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Ammonia Intoxication

Symptoms resulting from high ammonia levels in the blood, including tremors, slurred speech, drowsiness, and potentially coma/death.

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Hepatic Urea Cycle

The liver's ability to convert ammonia and produce urea.

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Urinary Urea Nitrogen (UUN)

The measurement of urea in urine, used to evaluate nitrogen excretion.

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Blood Urea Nitrogen (BUN)

The measurement of urea in blood, reflecting the activity of the urea cycle.

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Ammonia Production

Amines (from diet and hormones) and purines/pyrimidines (in catabolism) generate ammonia.

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Low Blood Ammonia Levels

Liver rapidly removes blood ammonia, and tissues release nitrogen as glutamine/alanine, not free ammonia.

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Urea Formation

The liver's main method to get rid of ammonia. Urea moves from liver to kidneys for excretion.

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Glutamine Formation

Glutamine is a non-toxic way to store and transport ammonia, using ATP. Primarily made in muscle and liver.

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Glutamine's Function

Glutamine transports ammonia in the blood and is the major method of removing ammonia in the brain. Also used in biosynthetic reactions.

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Monoamine Oxidase

An enzyme that helps produce ammonia from monoamines.

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Glutamate's Role

Glutamate is a key player in ammonia metabolism, participating in the synthesis of glutamine from ammonia.

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Ammonia Toxicity

High levels of ammonia are harmful to the central nervous system.

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Urea Cycle Regulation

Regulation of the urea cycle involves enzyme induction and substrate availability.

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Source of Ammonia

Amino acids are the primary source of ammonia in the body.

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NAG Role in Urea Cycle

N-acetylglutamate (NAG) activates the rate-limiting enzyme of the urea cycle, CPS I (carbamoyl phosphate synthetase I).

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Ammonia Disposal

The liver primarily handles ammonia disposal, converting it to urea.

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Amino Acid Catabolism

The breakdown of amino acids, removing their nitrogen-containing groups.

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Ammonia excretion

A portion of free ammonia is eliminated through urine.

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Glutamine Formation

Converting glutamate into glutamine to safely transport ammonia.

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Nitrogen Disposal

The process of removing excess nitrogen from the body.

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Urea Synthesis

The primary process of converting ammonia to urea for excretion.

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Urea Synthesis

The liver's primary process for eliminating nitrogen from the body.

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Alanine role in nitrogen disposal

Alanine carries nitrogen to the liver for urea production.

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Amino Acid Source

Amino acids come from diet, synthesis, or breakdown of body proteins.

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a-amino groups

The nitrogen-containing parts of amino acids that are removed during catabolism.

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Hyperammonemia causes

Liver diseases and deficiencies in urea cycle enzymes can lead to hyperammonemia.

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Amino acid degradation

Breakdown of proteins and amino acids in the body.

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Ammonia

A toxic byproduct of amino acid breakdown.

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a-keto acids

Carbon skeletons remaining after nitrogen removal from amino acids.

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Amino acid synthesis

The creation of amino acids to build proteins.

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Dietary protein degradation

The breakdown of dietary proteins.

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Nitrogen-containing molecules

Varied molecules that include dietary proteins as major sources, ultimately processed to urea, ammonia and other products.

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Amino group transfer

Transfer of amino groups to form a-keto acids.

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Nitrogen source

Amino acids are the primary source for nitrogen removal.

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Short-lived proteins

Proteins that are rapidly degraded, having half-lives in minutes or hours.

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Long-lived proteins

Proteins that are metabolically stable and have half-lives of days to weeks.

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Structural proteins

Proteins such as collagen; metabolically stable and have half-lives of months to years.

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Ubiquitin-proteasome system

An ATP-dependent enzyme system that degrades proteins, specifically targeting damaged or short-lived proteins.

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Lysosomes

Enzyme system that degrades intracellular and extracellular proteins, using acid hydrolases.

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Protein Degradation Methods

Two primary methods: Ubiquitin-proteasome system and lysosomes.

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Malate to Fumerate

A step in the Citric Acid Cycle, where Malate is converted to Fumerate. This reaction releases energy.

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Ornithine Regeneration

Ornithine is regenerated within the mitochondrial matrix during the Urea Cycle, following the synthesis of Citrulline.

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Citrulline Synthesis

Citrulline is synthesized within the mitochondrial matrix as part of the Urea Cycle.

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Citrulline Transport

The process of transporting Citrulline outside of the mitochondrial matrix to continue the Urea Cycle.

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L-Arginine

An amino acid involved in the Urea Cycle.

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L-Ornithine

One of the amino acids used in the urea cycle, important in recycling and transporting nitrogen.

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Urea Cycle Steps

A series of biochemical reactions to convert ammonia to urea, reducing toxicity.

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Ubiquitination Process

A three-step, enzyme-catalyzed, ATP-dependent process attaching ubiquitin to a target protein.

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Polyubiquitin Chain

Multiple ubiquitin molecules attached to a target protein, signaling for degradation.

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Proteasome

A large protein complex that recognizes and degrades polyubiquitinated proteins.

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Protein Degradation Signal

A structural aspect of a protein recognized by E3 ligase, triggering its degradation.

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E1 Enzyme

Activating enzyme that prepares ubiquitin for conjugation.

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E2 Enzyme

Conjugating enzyme that transfers ubiquitin to the target protein.

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E3 Enzyme

Ligase that identifies the target protein to be degraded and interacts with E2.

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Ubiquitin

A small protein that tags other proteins for degradation.

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Urea formation

The liver's main method of removing ammonia by converting it to urea.

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Amino acid breakdown

The process of removing nitrogen from amino acids, producing ammonia as a byproduct.

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Ammonia disposal

The liver primarily handles the conversion of ammonia into urea for safe excretion.

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Glutamine formation

The body converts glutamate into glutamine for safe transportation and storage of ammonia.

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Nitrogen atoms in urea

One nitrogen atom comes from an amino acid, and the other comes from bicarbonate.

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Free ammonia

A harmful byproduct of amino acid breakdown, produced in cells but not directly excreted.

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Source of nitrogen

Amino acids are a primary source of nitrogen in the body.

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Urea Cycle

A series of biochemical reactions that convert ammonia into urea, a less toxic compound for excretion, primarily in the liver.

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Ammonia

A toxic byproduct of amino acid breakdown that's converted to urea within the Urea Cycle.

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Argininosuccinate Cleavage

Argininosuccinate is broken down into arginine and fumarate by argininosuccinate lyase, a crucial step in the Urea Cycle.

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Arginine to Ornithine

Arginine is hydrolyzed to ornithine and urea by arginase-1, primarily in the liver; ornithine recycling for the cycle.

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Urea Excretion

Urea diffuses from the liver into the bloodstream, filtered by the kidneys and excreted in urine.

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Arginase-1

Liver enzyme that specifically cleaves arginine into ornithine and urea, crucial for Urea Cycle completion.

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Urea's Fate

Urea diffuses into the blood from liver, filtered by kidneys and eliminated in urine; some is also processed by bacteria in the intestine.

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Amino Acid Catabolism

The breakdown of amino acids to remove their nitrogen-containing groups, producing ammonia.

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Nitrogen Disposal

The process of removing excess nitrogen from the body, primarily through urea synthesis.

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Ammonia

A toxic byproduct of amino acid breakdown; converted to urea for excretion.

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Urea Synthesis

The liver's primary method for converting ammonia to urea for excretion.

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Urea Cycle

A series of biochemical reactions in the liver converting ammonia to urea for disposal.

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Amino Acid Source

Amino acids come from dietary protein, synthesis, or the breakdown of body protein.

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Free Ammonia

A harmful byproduct of amino acid breakdown produced inside cells, but not immediately excreted.

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Nitrogen-containing molecules

Various compounds, with dietary proteins as a major source, ultimately processed into urea, ammonia, and other products.

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Amino Acid Pool

A collection of free amino acids throughout the body (cells, blood, extracellular fluids) considered as a single entity for metabolic purposes.

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Protein Turnover

The simultaneous synthesis and degradation of protein molecules in the body.

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Amino Acid Pool Sources

The amino acid pool is supplied by endogenous protein degradation, dietary protein, and non-essential amino acid synthesis.

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Amino Acid Pool Depletion

Used for body protein synthesis, essential nitrogen-containing molecules, and conversion to other molecules (glucose, fatty acids).

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Protein Constant Amount (healthy adults)

In healthy adults, protein synthesis rate exactly balances protein degradation rate, maintaining a constant total protein amount.

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Dietary Protein Variation

Daily protein intake can vary widely, from zero to over 100 grams daily, but 100 grams per day is common in the U.S. diet.

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Study Notes

Amino Acids: Nitrogen Disposal

  • Amino acids are not stored in the body; they must be obtained from diet, synthesized, or produced from body protein breakdown.
  • Excess amino acids are degraded. This process begins by removing the amino group, forming ammonia and the corresponding a-keto acid.
  • Ammonia is partially excreted in the urine, but mostly used in urea synthesis (a key way the body disposes of nitrogen).
  • The second phase of amino acid catabolism involves the conversion of a-keto acids into common metabolic intermediates, yielding carbon dioxide, water, glucose, fatty acids, or ketone bodies.
  • Amino acid catabolism is part of a larger nitrogen metabolism process, where nitrogen enters the body primarily as amino acids from dietary protein and exits as urea, ammonia, and related byproducts (like creatinine).
  • The amino acid pool is a circulating pool of free amino acids in cells, blood, and extracellular fluids, a crucial part of protein synthesis.
  • Protein turnover is the constant synthesis and breakdown of proteins in the body. This maintains a steady-state protein concentration.
  • Short-lived proteins have fast turnover rates, while more stable proteins stay in the body longer.
  • Protein degradation is primarily controlled by either the ATP-dependent ubiquitin-proteasome system or the lysosome system.
  • Dietary protein digestion begins in the stomach with hydrochloric acid to denature proteins and activate the enzyme pepsinogen to pepsin.
  • Pancreatic enzymes (trypsin, chymotrypsin, elastase, carboxypeptidases) further break down proteins into smaller peptides and amino acids in the small intestine.
  • Amino acids are absorbed into the bloodstream by various transport systems (sodium-dependent and some independent).
  • Errors in amino acid absorption can lead to cystinuria, with specific amino acids appearing in the urine.

Dietary Protein Digestion

  • The body has specialized enzymes for protein digestion, located in different organs (stomach, pancreas, and small intestine).
  • Ubiquitin-proteasome system is the process where proteins are marked for degradation.
  • Proteasomes break down degraded proteins into smaller amino acids.

Nitrogen Removal from Amino Acids

  • Transamination is a key process that transfers amino groups from one molecule to another, often involving a specific amino acid and an a-keto acid.
  • Glutamate is a central amino acid in this process, acting as a recipient of amino groups from most other amino acids.
  • Aminotransferases are enzymes responsible for transamination functions.
  • Oxidative deamination is another important process, removing the amino group from glutamate to yield free ammonia directly.
  • Glutamate dehydrogenase catalyzes oxidative deamination of glutamate.
  • D-Amino acid oxidase is the enzyme that metabolizes D-amino acids to a-ketoacids in the liver and kidneys.

Urea Cycle

  • Urea is the primary way the body gets rid of nitrogenous waste.
  • The urea cycle is a series of enzymatic reactions that occur in the liver.
  • The cycle begins with the combination of ammonia, and bicarbonate to form carbamoyl phosphate, a crucial intermediate.
  • Carbamoyl phosphate synthetase I (CPS I) is the rate-limiting step. N-acetylglutamate activates CPS I.
  • Different enzymes are involved in the different stages of the urea cycle.
  • The cycle processes nitrogen from amino acids into urea, which is then released into the bloodstream.
  • The urea is filtered out and excreted by the kidneys.

Ammonia Metabolism

  • Ammonia is toxic at high levels and must be quickly removed.
  • The liver is a major site for ammonia disposal through urea cycle synthesis.
  • Two important ways to transport and remove ammonia are via glutamine, and alanine.
  • Glutamine acts as a temporary reservoir for ammonia and plays a key role in the transport and detoxification of ammonia.
  • Alanine is another important method. In this case, alanine conveys nitrogen to the liver for urea cycle conversion.
  • Ammonia levels elevated above normal are problematic and can lead to severe issues in the nervous system.

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Explore the critical process of amino acid catabolism and nitrogen disposal in the body. This quiz covers how excess amino acids are processed, the role of ammonia, and the conversion of a-keto acids. Understand the significance of the amino acid pool and protein turnover in overall metabolism.

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