The Many Fates of Nitrogen: Part 1 and Part 2

Flashcards based on lecture notes about nitrogen metabolism, amino acids, and related disorders, designed to help students prepare for exams.

What is nitrogen balance?

The difference between nitrogen intake (from proteins) and nitrogen excretion.

What are essential amino acids?

Amino acids that cannot be synthesized by the body and must be obtained through diet.

What is Kwashiorkor?

A form of protein malnutrition characterized by edema, stunted growth, and skin lesions.

What is Marasmus?

A severe form of malnutrition due to calorie deficiency, leading to extreme weight loss.

What is the role of trypsin?

A digestive enzyme that breaks down proteins in the small intestine.

What is the significance of the ubiquitin-proteasome system?

A mechanism that targets and degrades short-lived proteins using ATP.

What is the amino acid pool?

A reserve of amino acids available for protein synthesis and other metabolic processes.

What are glucogenic amino acids?

Amino acids that can be converted into glucose through gluconeogenesis.

What are ketogenic amino acids?

Amino acids that can be converted into ketone bodies.

What is the average daily protein intake recommended for adults to maintain nitrogen balance?

About 44 grams of protein per day.

What dietary sources can provide protein?

Eggs, meat, beans, and nut butter.

What happens in a negative nitrogen balance?

Nitrogen excretion exceeds nitrogen intake, usually due to malnutrition or illness.

What diseases are associated with negative nitrogen balance?

Wasting diseases, trauma, burns, and dialysis.

What is the importance of glutamine and arginine for patients with trauma?

They are conditionally essential amino acids that may benefit recovery.

What role does ammonia play in nitrogen metabolism?

Ammonia is produced from amino acid deamination and is converted to urea for excretion.

How is urea formed in the body?

Via the urea cycle in the liver, converting ammonia and aspartate.

What are the steps of the urea cycle?

Conversion of ammonia and aspartate to urea through a series of enzymatic reactions.

What is the consequence of urea cycle deficiency?

Hyperammonemia, which can cause neurological damage.

What hormones influence protein digestion?

Gastrin, cholecystokinin (CCK), and secretin.

What is the function of pepsin?

A digestive enzyme that breaks down proteins in the stomach.

What is the primary effect of glucagon on nitrogen metabolism?

Stimulates gluconeogenesis and amino acid usage for energy during fasting.

What is the role of bile salts in digestion?

They help emulsify fats and aid in fat digestion.

What does the term 'protein turnover' refer to?

The continuous process of protein synthesis and degradation.

What can cause hyperammonemia?

Urea cycle disorders or liver diseases that impair ammonia disposal.

What impact does age have on protein needs?

Protein requirements increase during growth phases like pregnancy.

What are the two major classes of amino acids?

Essential and nonessential amino acids.

How are amino acids absorbed in the intestine?

Through specific solute carrier (SLC) proteins in the intestinal epithelium.

What is transamination?

The transfer of an amino group from one amino acid to a keto acid.

What is the function of aspartate in the urea cycle?

It contributes nitrogen to urea by combining with ammonia.

What is homocystinuria?

A condition caused by a defect in cystathionine beta-synthase, leading to high homocysteine levels.

What dietary changes can help treat phenylketonuria (PKU)?

Strictly limiting phenylalanine intake and increasing tyrosine.

What are zymogens?

Inactive enzyme precursors that require activation to function.

What enzyme activates trypsinogen?

Enteropeptidase activates trypsinogen to trypsin in the intestine.

What is the role of N-acetylglutamate in the urea cycle?

It activates carbamoyl phosphate synthetase I (CPS I).

What types of proteins undergo rapid turnover?

Short-lived regulatory proteins and misfolded proteins.

What factors can affect the rate of protein synthesis?

Nutritional status, hormonal changes, and tissue demands.

What is the significance of alanine in gluconeogenesis?

It transports nitrogen to the liver and serves as a substrate for glucose synthesis.

What is cystinuria?

An inherited disorder affecting the uptake of cystine and some other basic amino acids.

How does the body dispose of excess nitrogen?

By converting it into urea, which is excreted in urine.

What is the main risk associated with untreated homocystinuria?

Increased risk of thrombosis or stroke.

What does the term 'conditional amino acids' refer to?

Amino acids that are normally nonessential but become essential under specific circumstances.

What enzyme is deficient in maple syrup urine disease?

Branched-chain alpha-keto acid dehydrogenase.

What does excessive phenylalanine lead to?

Neurotoxic effects due to the accumulation of metabolites.

What are the signs of cystinuria?

Kidney stones caused by the accumulation of cystine.

What role do proteases play in digestion?

They hydrolyze protein into peptides and amino acids.

What happens to the amino acids not used in biosynthesis?

They are burned for energy or converted into other compounds.

What are the products of the urea cycle?

Urea and fumarate.

What is hyperphenylalaninemia?

An excess of phenylalanine in the blood, characteristic of PKU.

What is the function of cystathionine beta-synthase?

It catalyzes the conversion of homocysteine to cysteine.

What is the metabolic fate of branched-chain amino acids?

They are primarily oxidized for energy and not used for gluconeogenesis.

What is the major storage form of nitrogen in the body?

Urea.

What can be the result of amino acid oxidation?

Producing energy and nitrogen waste that is excreted.

What happens during oxidative deamination?

Removal of the amino group from an amino acid, producing ammonia and a keto acid.

What is the diagnostic test for urea cycle disorders?

Measuring levels of ammonia and orotic acid in blood and urine.

What are the potential consequences of untreated phenylketonuria?

Severe intellectual disability and other neurological problems.

What is the role of the liver in amino acid metabolism?

It is the central site for amino acid catabolism and urea synthesis.

What is the key reaction catalyzed by glutamate dehydrogenase?

The oxidative deamination of glutamate to produce ammonia.

What metabolic pathways connect amino acid and carbohydrate metabolism?

Transamination and gluconeogenesis.

What are the two primary processes affecting amino acid balance in the body?

Protein synthesis and degradation.

What is the relationship between nitrogen excretion and protein intake?

Higher protein intake leads to increased nitrogen excretion as urea.

What is an example of a conditionally essential amino acid?

Arginine—essential during periods of growth or stress.

What can cause protein energy malnutrition?

Inadequate protein and calorie intake.

What is a common symptom of Kwashiorkor?

Swelling or edema due to protein deficiency.

What happens to amino acids during fasting?

They are released from body proteins and used for energy.

Why is dietary protein intake variable?

Due to differences in dietary habits, availability, and physiological needs.

How are ammonia levels regulated in the body?

Through the urea cycle and synthesis of glutamine.

What nutrients are required to support amino acid synthesis?

Vitamin B6 (pyridoxal phosphate) and other cofactors.

What is the nitrogenous waste primarily excreted by humans?

Urea.

What role do dietary carbohydrates play in amino acid metabolism?

They provide energy and can influence nitrogen balance.

What is the effect of insulin on amino acid metabolism?

It promotes amino acid entry into cells and protein synthesis.

What is the function of amino acid transporters in the kidney?

To reabsorb amino acids from urine back into the blood.

What is the significance of CCK in protein digestion?

It stimulates the release of digestive enzymes and bile salts.

What can lead to a positive nitrogen balance?

States of growth, pregnancy, or recovery from illness.

What is the primary means of nitrogen disposal during starvation?

Increased use of amino acids for gluconeogenesis and energy.

What are the symptoms of phenylketonuria?

Intellectual disability, seizures, and hypopigmentation.

What is the mechanism by which ammonia is detoxified in the liver?

Incorporation into urea via the urea cycle.

What metabolic pathway is activated by high protein consumption?

The urea cycle, to handle increased nitrogen.

What are the types of post-translational modifications that proteins can undergo?

Phosphorylation, acetylation, and ubiquitination.

What metabolic fates do excess amino acids have?

Conversion to glucose, fatty acids, or urea.

What is the effect of glucagon on amino acid metabolism?

It promotes the release of amino acids from muscle into the bloodstream.

What enzyme catalyzes the formation of urea in the urea cycle?

Arginase, which converts arginine to urea.