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Questions and Answers
What is produced when DNA is transcribed?
What is produced when DNA is transcribed?
Translation of mature mRNA occurs in the nucleus.
Translation of mature mRNA occurs in the nucleus.
False
What type of bonding stabilizes the primary structure of proteins?
What type of bonding stabilizes the primary structure of proteins?
Peptide bonds
The tertiary structure of a protein describes its _____ overall fold.
The tertiary structure of a protein describes its _____ overall fold.
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Match the following protein structures with their descriptions:
Match the following protein structures with their descriptions:
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Which enzyme is essential for the glucose-alanine cycle?
Which enzyme is essential for the glucose-alanine cycle?
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Fumarate is produced by glutamate in the urea cycle.
Fumarate is produced by glutamate in the urea cycle.
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What intermediate connects the Krebs cycle and the urea cycle?
What intermediate connects the Krebs cycle and the urea cycle?
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The enzyme that initiates the urea cycle requires _____ as an allosteric effector.
The enzyme that initiates the urea cycle requires _____ as an allosteric effector.
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Match the following enzymes with their roles in the urea cycle:
Match the following enzymes with their roles in the urea cycle:
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What is one of the main functions of the glucose-alanine cycle?
What is one of the main functions of the glucose-alanine cycle?
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Ornithine transcarbamylase (OTC) cleaves argininosuccinate into fumarate and arginine.
Ornithine transcarbamylase (OTC) cleaves argininosuccinate into fumarate and arginine.
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What accumulates when the urea cycle is blocked after CPS1?
What accumulates when the urea cycle is blocked after CPS1?
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The reaction catalysed by argininosuccinate lyase cleaves argininosuccinate into _____ and arginine.
The reaction catalysed by argininosuccinate lyase cleaves argininosuccinate into _____ and arginine.
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What is the primary cause of enhanced fibrinolytic activity in chronic liver disease?
What is the primary cause of enhanced fibrinolytic activity in chronic liver disease?
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Disseminated intravascular coagulation results in blood clots forming only in large blood vessels.
Disseminated intravascular coagulation results in blood clots forming only in large blood vessels.
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What happens to surplus amino acids in the fed state?
What happens to surplus amino acids in the fed state?
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Ammonia is detoxified in the body by converting it into ______ for urinary excretion.
Ammonia is detoxified in the body by converting it into ______ for urinary excretion.
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Match the following components of the glucose-alanine cycle with their functions:
Match the following components of the glucose-alanine cycle with their functions:
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How does chronic liver disease primarily affect clotting factors?
How does chronic liver disease primarily affect clotting factors?
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The development of varices is a vascular complication associated with chronic liver disease.
The development of varices is a vascular complication associated with chronic liver disease.
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What happens to muscle proteins during fasting or starvation?
What happens to muscle proteins during fasting or starvation?
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The principal ammonia scavenger and transporter in muscle is ______.
The principal ammonia scavenger and transporter in muscle is ______.
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Which clotting factors are synthesized in the liver?
Which clotting factors are synthesized in the liver?
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Factor III is produced by the liver.
Factor III is produced by the liver.
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What is the function of gamma-glutamyl carboxylase enzyme in the liver?
What is the function of gamma-glutamyl carboxylase enzyme in the liver?
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Vitamin K is essential for the synthesis of factors _____, _____, _____, and _____.
Vitamin K is essential for the synthesis of factors _____, _____, _____, and _____.
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Match the following clotting factors with their sites of synthesis:
Match the following clotting factors with their sites of synthesis:
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How does chronic liver disease contribute to reduced synthesis of clotting factors?
How does chronic liver disease contribute to reduced synthesis of clotting factors?
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Chronic liver disease can lead to Vitamin K deficiency.
Chronic liver disease can lead to Vitamin K deficiency.
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Study Notes
Protein Synthesis and the Urea Cycle
- Learning Objectives: Cover albumin synthesis, function, and clinical significance; clotting factor synthesis, function, and clinical significance; urea cycle, role in metabolism, ammonia neurotoxicity, and urea cycle disorders. Also explores protein synthesis, transcription/translation location, mRNA maturation and protein modifications. Discusses protein structure. Details the role of the liver in protein synthesis and the clotting cascade. Explores clinical conditions, like chronic liver disease and its relation to bleeding. Examines ammonia toxicity, clinical signs, and treatment.
Protein Synthesis
- Pre-mRNA is produced when DNA is transcribed.
- Transcription occurs in the nucleus.
- Mature mRNA is generated through post-transcriptional modifications such as 5' capping, 3' Poly-A tail addition.
- Mature mRNA enters the cytoplasm through nuclear pores.
- Translation of mature mRNA happens in ribosomes.
- Protein folding and post-translational modifications happen after translation.
- The primary structure of a protein is a polypeptide chain.
Protein Structure
- Peptide bonds stabilize the primary structure of proteins.
- Secondary structures include alpha helices and beta sheets, stabilized by different types of hydrogen bonds.
- The tertiary structure of a protein is the overall 3D fold incorporating secondary structures.
- Quaternary structures exist in multi-subunit complexes, where each subunit is a distinct polypeptide chain.
Major Proteins Synthesized in the Liver
- The liver synthesizes albumin, CRP, hormone-binding globulins, apolipoproteins, other transport proteins, caeruloplasmin, and ferritin.
- Albumin is the primary plasma protein maintaining oncotic pressure.
- The liver is crucial in various metabolic pathways.
Clotting Cascade
- The liver synthesizes most clotting factors.
- Clotting factors like factor III, IV, and VIII are exceptions in the liver's clotting factor synthesis.
Vitamin K
- Vitamin K is essential for the synthesis of clotting factors X, IX, VII, and II and the gamma-glutamyl carboxylase enzyme.
Urea Cycle
- Surplus amino acids are processed into glucose, glycogen, fatty acids or oxidized to produce ATP.
- During fasting or starvation, muscle proteins are broken down to yield amino acids for gluconeogenesis, maintaining blood glucose levels.
- Ammonia, a byproduct of amino acid metabolism, is extremely toxic and must be detoxified.
- Ammonia is converted into urea for urinary excretion in the liver.
- Ammonia that evades detoxification is incorporated into glutamine by glutamine synthetase.
- Fumarate acts as a connecting link between the Krebs and urea cycles.
Glucose-Alanine Cycle
- Alanine is the principal ammonia scavenger and transporter in muscle.
- Ammonia from muscle is attached to alanine.
- Glutamate collects ammonia in muscle.
- Alanine aminotransferase (ALT) transfers the amino group from glutamate to pyruvate.
Urea Cycle Disorders
- These disorders are characterized by the buildup of ammonia, leading to various problems, including cerebral edema, impaired brainstem function, and potentially life-threatening symptoms.
Ammonia Toxicity
- The oculocephalic reflex is relevant to assessing ammonia toxicity.
- Decerebrate posturing in ammonia toxicity signifies brain stem damage or dysfunction.
- Characteristics include rigid extension of limbs, plantar flexion of feet, and backward arching of the head.
- Ammonia disrupts brain metabolism, causing cerebral edema and impaired brainstem function.
Conditions Associated with Elevated Ammonia
- Loss of liver cells (toxins or viruses) and blood bypassing the liver (cirrhosis) may elevate ammonia.
- Ammonia crosses the blood-brain barrier easily, depleting a-ketoglutarate, stopping the citric acid cycle, and leading to cell damage and death.
Treatment and Dietary Modifications
- Treatment may include providing glucose to induce anabolism, and dietary adjustments (low protein diet, supplements like arginine). Ammonia buildup is targeted in treatment.
Other Important Considerations
- The glutamine hypothesis explains ammonia neurotoxicity.
- Two major consequences are cerebral edema and neural cell death.
- Advanced treatment options include haemofiltration, liver transplantation, or umbilical vein hepatocyte transfusion.
- Oral emergency regimens are used to manage urea cycle defects, starting at the first symptom.
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Description
Test your understanding of protein synthesis, albumin production, and the urea cycle. This quiz covers key concepts such as transcription, translation, and clinical implications related to protein metabolism and liver function. Identify disorders related to the urea cycle and their impact on health.
