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Questions and Answers
What condition results from defects in the conversion of ammonia to urea?
Which enzyme deficiency is associated with severe neonatal disorder and fatal consequences?
What is the primary consequence of increased ammonia levels in the brain?
What condition is characterized by hyper-ornithinemia, hyperammonemia, and homocitrillinuria?
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What is the role of S-adenosylmethionine (SAM) in methionine metabolism?
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What can result from methionine metabolism beyond cysteine production?
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What neurological symptoms can result from hyperammonaemia?
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Which enzyme action alters DNA accessibility through modification of histone proteins?
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What is the first product formed in the urea cycle?
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Which of the following compounds is NOT a substrate for Carbamoyl phosphate synthetase I (CPS I)?
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Which enzyme requires N-acetylglutamate (NAG) for its activity?
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What is the primary nitrogen source in the synthesis of urea from the urea cycle?
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Which step in the urea cycle is considered rate-limiting?
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What is the end product of the protein metabolism process involving the urea cycle?
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From which organ are urea molecules transported for excretion?
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What is the major difference between Carbamoyl phosphate synthetase I (CPS I) and Carbamoyl phosphate synthetase II (CPS II)?
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What is one primary way ammonia (NH4+) is handled in the body following amino acid degradation?
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Which statement is true regarding the amino acid pool in the body?
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What role do certain amino acids play beyond being building blocks for proteins?
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Which of the following best describes the dynamics of protein turnover in the body?
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How are essential amino acids generally obtained by animals?
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What is the relationship between tyrosine and phenylalanine in the body?
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What distinguishes essential amino acids from nonessential amino acids?
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Which molecule can arginine be derived from in the body?
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Which amino acids do not participate in transamination?
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What is the first step in the mechanism of transamination?
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Where does transamination predominantly occur?
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Which enzyme is specifically found in the liver mitochondria to perform oxidative deamination?
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What compound does glutamate dehydrogenase produce during oxidative deamination?
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What is a consequence of cellular damage in relation to enzymatic activity?
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Which of the following describes the role of glutamate in amino acid metabolism?
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What is the main purpose of oxidative deamination?
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What substance accumulates in the urine of individuals with PKU due to the enzyme deficiency?
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What is the inheritance pattern of Phenylketonuria (PKU)?
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Who first described Phenylketonuria and related it to the urine's musty odor?
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Which gene mutation is directly associated with Phenylketonuria?
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What is one of the common symptoms of PKU?
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What dietary management is typically used to treat PKU?
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What is a characteristic physical feature associated with PKU?
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What is a potential consequence of not adhering to the dietary restrictions for PKU?
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Study Notes
Amino Acid Degradation
- Amino acid degradation results in ammonium (NH4+) and carbon skeletons.
- NH4+ can be converted into nitrogen-containing compounds like nucleotides or excreted as urea.
- Carbon skeletons can enter TCA cycle intermediates for ATP production, fatty acid synthesis, or gluconeogenesis.
Functions of Amino Acids
- Certain amino acids act as neurotransmitters, including glycine, aspartate, and glutamate.
- The body contains approximately 100g of free amino acids as an amino acid pool.
- Glutamate and glutamine make up about 50% of the amino acid pool; essential amino acids account for around 10%.
- Intracellular amino acid concentration exceeds that of extracellular; cellular uptake occurs against a concentration gradient.
Sources and Turnover of Amino Acids
- The amino acid pool is maintained through dietary protein intake and synthesis of non-essential amino acids.
- Body protein turnover involves 300-400g of protein being constantly degraded and synthesized daily.
Essential and Nonessential Amino Acids
- Essential amino acids must be obtained through diet; they have more complex structures and require numerous enzymatic reactions for synthesis.
- Conditional essential amino acids include tyrosine (derived from phenylalanine) and arginine (partially synthesized from argininosuccinate).
Transamination Mechanism
- Transamination involves transferring the amino group from an amino acid to an α-keto acid, producing a new amino acid and a keto acid.
- The process utilizes pyridoxal phosphate (PLP) as a coenzyme, facilitating amino group transfer.
Transamination and Deamination
- Transamination occurs in the cytoplasm, converting amino acids while transporting amino groups as glutamic acid to the liver.
- Deamination removes an amino group from amino acids as NH3, contributing to urea synthesis from liberated ammonia.
Glutamate Dehydrogenase (GDH)
- GDH, found in liver mitochondria, converts glutamate to α-ketoglutarate and ammonia.
- GDH is regulated allosterically, activated by ADP and inhibited by GTP.
Urea Cycle
- Urea is synthesized in the liver and transported to kidneys for excretion, comprising two nitrogen atoms from ammonia and aspartic acid.
- The urea cycle consists of five steps involving specific enzymes; initial steps occur in mitochondria while the latter steps take place in the cytosol.
Enzyme Regulation and Deficiencies
- Carbamoyl phosphate synthetase I (CPS I) initiates urea production by converting NH4+ and CO2 into carbamoyl phosphate, requiring N-acetylglutamate for activity.
- Disorders of urea metabolism lead to hyperammonaemia, resulting from inherited or acquired enzyme deficiencies.
Methionine Metabolism
- Methionine is vital for epigenetic regulation and cysteine production, influencing gene expression through methylation processes.
Phenylketonuria (PKU)
- PKU is an autosomal recessive disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene, leading to mental retardation and other symptoms.
- An early 20th-century case study identified the condition, originally named 'imbecillitas phenylpyruvica.'
- Management involves a strict low-protein diet to mitigate symptoms and improve health outcomes.
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Description
This quiz explores the processes involved in amino acid degradation, focusing on the production of ammonium and carbon skeletons. It covers their roles in synthesizing nitrogen-containing compounds and generating ATP, highlighting their importance in metabolism and energy production.
