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Questions and Answers
Match the following enzymes with their primary function:
Match the following enzymes with their primary function:
Glutaminase = Removes nitrogen and generates glutamate Asparaginase = Breaks down asparagine L Amino Acid Oxidase = Generates peroxide from L amino acids D Amino Acid Oxidase = Breaks down D amino acids and generates peroxide
Match the following processes with their descriptions:
Match the following processes with their descriptions:
Glucose-Alanine Cycle = Converts alanine to pyruvate Urea Cycle = Converts ammonia to urea Ammonia trapping in urine = Decreases toxicity by forming ammonium ion Catalase action = Detoxifies peroxide in peroxisomes
Match the following nitrogen-related substances with their toxicity levels:
Match the following nitrogen-related substances with their toxicity levels:
Ammonia = Toxic at levels greater than 10 micrograms per liter Ammonium ion = Toxic at levels around half a milligram Urea = Less toxic compared to ammonia Glutamate = Non-toxic nitrogen carrier
Match the following components of the glucose-alanine cycle with their functions:
Match the following components of the glucose-alanine cycle with their functions:
Match the following conditions with their implications:
Match the following conditions with their implications:
Match the urea cycle enzymes with their corresponding reactions:
Match the urea cycle enzymes with their corresponding reactions:
Match the urea cycle reactants with their products:
Match the urea cycle reactants with their products:
Match the conditions with their implications regarding the urea cycle:
Match the conditions with their implications regarding the urea cycle:
Match the following compounds with their roles in the urea cycle:
Match the following compounds with their roles in the urea cycle:
Match the process steps with their corresponding enzymes:
Match the process steps with their corresponding enzymes:
Match the following enzymes with their specific substrates:
Match the following enzymes with their specific substrates:
Match the enzyme activation to its triggering molecules:
Match the enzyme activation to its triggering molecules:
Match the following urea cycle defects with their descriptions:
Match the following urea cycle defects with their descriptions:
Match the urea cycle enzymes with their functions:
Match the urea cycle enzymes with their functions:
Match the components with their roles in hyperammonemia treatment:
Match the components with their roles in hyperammonemia treatment:
Match the locations of urea cycle enzymes with their respective compartments:
Match the locations of urea cycle enzymes with their respective compartments:
Match the urea cycle intermediates with their descriptions:
Match the urea cycle intermediates with their descriptions:
Match the treatment approaches for hyperammonemia with their effects:
Match the treatment approaches for hyperammonemia with their effects:
Match the signs and symptoms of urea cycle defects with their implications:
Match the signs and symptoms of urea cycle defects with their implications:
Match the following terms with their associated effects in the urea cycle:
Match the following terms with their associated effects in the urea cycle:
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Study Notes
Urine and Ammonia
- Urine is acidic and traps ammonia as the ammonium ion, decreasing the toxicity of the ammonia.
- Ammonia is far more toxic than the ammonium ion.
Glutaminase and Asparaginase
- Glutaminase removes nitrogen and generates glutamate and glutamine.
- Glutamine can be thought of as an intracellular carrier of nitrogen.
- Asparaginase is an enzyme that exists, but typically not an issue.
L and D Amino Acid Oxidase Enzymes
- L Amino Acid Oxidase requires FMN (flavine mononucleotide) and generates peroxide.
- D Amino Acid Oxidase uses FAD and generates peroxide.
- This enzyme is important for breaking down D amino acids, which are typically found in bacterial infections.
The Glucose-Alanine Cycle (Cahill Cycle)
- The glucose-alanine cycle conserves glucose backbones.
- It involves converting alanine to pyruvate and back to glucose in the liver.
- This cycle sustains glucose usage in the brain and red blood cells.
- It prevents glucose breakdown into fatty acids and ketone bodies in muscle cells.
The Importance of Catalase
- Catalase detoxifies peroxide generated by L and D amino acid oxidases.
- Catalase is found in peroxisomes.
Ammonia Toxicity
- Ammonia levels greater than 10 micrograms per liter are toxic to cells.
- The ammonium ion is less toxic, with a toxic level of around half a milligram.
- There is a 100-fold higher concentration of ammonium ion than ammonia under physiological conditions.
Urea Cycle
- A complete block in any step of the urea cycle is incompatible with life.
- The urea cycle is a crucial process in the liver.
- It converts nitrogen from ammonia into urea, which is then excreted.
- The urea cycle is split between the mitochondrion and the cytosol.
Location of Enzymes
- The first two enzymes of the urea cycle are located in the mitochondrial matrix.
- The remaining three enzymes are located in the cytosol.
Carbonyl Phosphate Synthetase 1 (CPS 1)
- CPS 1 is the first enzyme of the urea cycle.
- It catalyzes the reaction between bicarbonate and ammonium ion to form carbonyl phosphate.
- Carbonyl phosphate is an activated form of urea, with a phosphate group on one end and a nitrogen group on the other.
Ornithine Transcarbamylase
- Ornithine transcarbamylase is the second enzyme of the urea cycle.
- It catalyzes the reaction between ornithine and carbamyl phosphate to form citrulline.
Urea Cycle Reactions
| Enzyme | Reactants | Products |
|---|---|---|
| CPS 1 | Bicarbonate, Ammonium ion | Carbonyl phosphate |
| Ornithine Transcarbamylase | Ornithine, Carbamyl phosphate | Citrulline |
| Arginosuccinate Synthetase | Citrulline, Aspartate | Arginosuccinate |
| Arginosuccinate Lyase | Arginosuccinate | Arginine |
| Arginase | Arginine | Urea |
Hyperammonemia
- High levels of ammonia in the blood.
- Deficiencies in enzymes of the urea cycle can lead to hyperammonemia.
Activation of the Urea Cycle
- The urea cycle is activated by the flow of nitrogen.
- The enzyme N-Acetylglutamate Synthetase regulates this.
- N-Acetylglutamate Synthetase generates N-Acetylglutamate, which activates Carbonyl Phosphate Synthetase 1.
Urea Precursors
- The urea precursors provide nitrogen for the urea cycle.
- They include:
- Aspartate
- Free ammonium ion
- Carbamyl phosphate
Hyperammonemia
- Hyperammonemia results from urea cycle deficiencies.
- Consists of 2 main enzymes: Carbamylphosphate Synthetase 1 (CPS 1) and Ornithine Transcarbamylase (OTC)
- CPS 1 is the rate-limiting enzyme, regulated by N-Acetylglutamate.
Hyperammonemia Process
- Ammonium ion + Bicarbonate → Carbamylphosphate (via CPS 1)
- Carbamylphosphate → Citrulline (via OTC)
- Citrulline → Argininosuccinate (via Argininosuccinate Synthetase)
- Argininosuccinate → Arginine (via Argininosuccinate Lyase)
- Arginine → Urea (via Arginase)
- Urea → Ornithine (via Arginase)
Hyperammonemia diagnosis
- Elevated ammonia levels
- Decreased BUN levels
- Increased blood glutamine levels
Enzyme Deficiencies
- Ornithine Transcarbamylase (OTC) Deficiency
- Symptoms:
- Hyperammonemia
- Elevated carbamylphosphate levels
- Elevated orotic acid levels (due to artificial stimulation of pyrimidine biosynthesis)
- Diagnosis: Orotic acid urea
- Symptoms:
- Carbamylphosphate Synthetase 1 (CPS 1) Deficiency
- Symptoms:
- Hyperammonemia
- Decreased carbamylphosphate levels
- Decreased orotic acid levels
- Diagnosis: No orotic acid urea
- Symptoms:
Clinical Signs and Symptoms
- Central edema
- Lethargy
- Convulsions
- Coma
- Death
- Ammonia can cross the blood-brain barrier, leading to central edema.
Summary
| Enzyme Deficiency | Symptoms | Diagnosis |
|---|---|---|
| OTC Deficiency | Hyperammonemia, Elevated Carbamylphosphate, Elevated Orotic Acid | Orotic Acid Urea |
| CPS 1 Deficiency | Hyperammonemia, Decreased Carbamylphosphate, Decreased Orotic Acid | No Orotic Acid Urea |
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