Biochemistry urea cycle and amino acid metabolism flashcards

What is the primary function of the urea cycle?

To convert ammonia, a toxic byproduct of amino acid metabolism, into urea for excretion.

Name the key starting substrate of the urea cycle.

Ammonia (NH₃) is the key starting substrate.

Identify the first enzyme in the urea cycle.

Carbamoyl phosphate synthetase I (CPS I) catalyzes the first step.

True or False: The urea cycle occurs in both mitochondria and cytosol.

True. The cycle has steps in both mitochondria and cytosol.

Fill in the blank: The final product of the urea cycle is _____.

Urea.

What role does ornithine play in the urea cycle?

Ornithine acts as a carrier to facilitate the cycle; it combines with carbamoyl phosphate.

List two key regulatory molecules of the urea cycle.

- N-acetylglutamate - Ammonia (NH₃)

Compare carbamoyl phosphate and urea.

Carbamoyl phosphate is an intermediate; urea is the end product excreted.

What is the role of arginase in the urea cycle?

Arginase catalyzes the conversion of arginine to urea and ornithine.

How many ATP are consumed in the urea cycle?

Two ATP molecules are consumed in the formation of carbamoyl phosphate.

True or False: The urea cycle is only active during fasting.

False. It is always active but increases during protein-rich diets.

What is the connection between the urea cycle and the citric acid cycle?

Fumarate, produced in the urea cycle, can enter the citric acid cycle.

Identify the second enzyme of the urea cycle.

Ornithine transcarbamylase (OTC) is the second enzyme.

What is the significance of N-acetylglutamate?

It activates carbamoyl phosphate synthetase I, enhancing urea cycle activity.

Cause → Effect: Elevated ammonia levels lead to _____.

Increased urea cycle activity to detoxify ammonia.

List the steps of the urea cycle.

- Synthesis of carbamoyl phosphate - Formation of citrulline - Conversion to argininosuccinate - Cleavage to arginine and fumarate - Hydrolysis of arginine to urea and ornithine

What are essential amino acids?

Essential amino acids cannot be synthesized by the body and must be obtained from the diet. Examples include leucine, isoleucine, and valine.

True or False: All amino acids are essential.

False. Only nine amino acids are essential; the rest can be synthesized by the body.

List the three branched-chain amino acids (BCAAs).

Leucine, isoleucine, valine.

What is amino acid catabolism?

Amino acid catabolism is the process by which amino acids are broken down to generate energy or to produce other compounds. It primarily occurs in the liver.

Fill in the blank: The main nitrogenous waste from amino acid catabolism is _____ .

urea.

Compare transamination and deamination.

- Transamination: Transfer of an amino group to a keto acid. - Deamination: Removal of an amino group, resulting in ammonia.

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

The liver is crucial for amino acid catabolism, conversion to glucose, and urea cycle processing. It regulates the distribution of amino acids to other tissues.

True or False: Amino acids can be converted directly to fatty acids.

True. Excess amino acids can be converted to fatty acids through gluconeogenesis and lipogenesis.

What are non-essential amino acids?

Non-essential amino acids can be synthesized by the body. Examples include alanine, aspartate, and serine.

Cause → Effect: What happens if dietary protein is insufficient?

Inadequate protein leads to muscle wasting, impaired immune function, and reduced synthesis of hormones and enzymes.

Short example of amino acid synthesis.

For instance, serine can be synthesized from glycine via serine hydroxymethyltransferase.

Which pathways involve amino acid synthesis?

Key pathways include the Krebs cycle, glycolysis, and various transamination reactions.

What is phenylketonuria (PKU)?

A genetic disorder causing phenylalanine accumulation due to phenylalanine hydroxylase deficiency. Symptoms include intellectual disability and seizures.

Map the urea cycle's role.

Converts ammonia to urea. Prevents toxic ammonia accumulation. Key in nitrogen metabolism.

True or False: Arginine is essential for adults.

False. Arginine is conditionally essential; needed in higher amounts during stress or illness.

Compare Maple Syrup Urine Disease (MSUD) and PKU.

- MSUD: Branched-chain amino acid metabolism disorder. - PKU: Phenylalanine metabolism disorder. Different amino acids affected, leading to varied symptoms.

Fill in the blank: Ornithine transcarbamylase deficiency leads to __________.

hyperammonemia due to impaired urea cycle function.

What causes Alkaptonuria?

A deficiency in homogentisate oxidase leads to accumulation of homogentisic acid, causing dark urine and joint issues.

True or False: The urea cycle occurs primarily in the mitochondria.

True. The urea cycle takes place mainly in liver mitochondria and cytosol.

What is the effect of citrullinemia?

Caused by argininosuccinate synthetase deficiency, leads to ammonia accumulation, and requires dietary protein restriction.

Name two disorders related to amino acid metabolism.

- Phenylketonuria (PKU) - Maple Syrup Urine Disease (MSUD)

How does liver disease affect amino acid metabolism?

Impaired urea cycle function leads to ammonia toxicity. Symptoms include lethargy and confusion.

List the main products of amino acid catabolism.

- Ammonia - Carbon skeletons - Energy (ATP)

What is the link between urea cycle disorders and neurological symptoms?

Accumulation of toxic ammonia affects neurotransmitter synthesis, leading to symptoms like confusion, seizures, and coma.