Biochemistry Urea Cycle and Citric Acid Cycle Quiz

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Questions and Answers

What is the only product generated in the urea cycle?

Citrulline

Arginine

Urea (correct)

Fumarate

In which part of the cell do the first two reactions of the urea cycle occur?

Nucleus

Mitochondria (correct)

Cytoplasm

Endoplasmic Reticulum

Which molecule combines with ammonia and carbon dioxide to initiate the urea cycle?

Arginino succinate

N-acetyl glutamate

Ornithine

Carbamoyl phosphate (correct)

What is the total ATP consumption for the synthesis of one molecule of urea in the urea cycle?

2 ATP Signup and view all the answers

Which intermediate is formed from the combination of ammonia and carbon dioxide within the urea cycle?

Citrulline Signup and view all the answers

What is the significance of elevated ALT levels in the diagnosis of Hepatitis?

It indicates liver injury more accurately than AST Signup and view all the answers

During the Citric Acid Cycle, which component is primarily associated with filling up reactions?

Citrate Signup and view all the answers

Which of the following enzymes would you expect to have increased activity due to liver damage in Hepatitis?

Alanine aminotransferase (ALT) Signup and view all the answers

What can be inferred if both ALT and AST levels are elevated, but ALT is significantly higher in a patient?

This is characteristic of acute liver conditions Signup and view all the answers

In the context of the Citric Acid Cycle, what role does oxaloacetate play?

It combines with acetyl-CoA to form citrate Signup and view all the answers

What effect does a protein-free diet have on enzyme levels?

It decreases enzyme levels. Signup and view all the answers

Which statement accurately reflects the role of L-Glutamate Dehydrogenase?

It produces ammonia ($NH_3$) from L-Glutamate. Signup and view all the answers

What is the consequence of increased dietary protein or starvation on enzyme levels?

It increases enzyme levels. Signup and view all the answers

What is the function of N-Acetyl Glutamate in the urea cycle?

It acts as an activator of CPS-I. Signup and view all the answers

Which of the following is true regarding starvation's impact on enzyme levels?

Starvation increases the levels of many enzymes. Signup and view all the answers

What is the primary fate of urea produced in the liver?

It is released into the blood and then filtered by the kidneys. Signup and view all the answers

What is the role of bacterial urease in the intestine with respect to bile urea?

It hydrolyzes bile urea to carbon dioxide and ammonia. Signup and view all the answers

What percentage of ammonia is converted to urea in the liver through the urea cycle?

90% Signup and view all the answers

Which organ is primarily responsible for the excretion of ammonia in urine?

Kidney Signup and view all the answers

Where is most urea excreted from the body?

It is mostly excreted in urine by the kidneys. Signup and view all the answers

What concentration range of urea can typically be found in the blood?

10-50 mg/dL Signup and view all the answers

During acidosis, which amino acid is primarily synthesized for ammonia handling in the body?

Glutamine Signup and view all the answers

Which compound is formed through the transamination of glutamate and oxaloacetate?

Aspartate Signup and view all the answers

What percentage of urinary ammonia is excreted by the kidneys?

40% Signup and view all the answers

Which of the following statements about the urea cycle is NOT correct?

It results in the excretion of ammonia directly in urine. Signup and view all the answers

What is the product of the enzymatic reaction involving Homoserine Deaminase?

a-Keto Glutarate Signup and view all the answers

Which enzyme is responsible for converting Glutamine into Glutamate?

Glutaminase Signup and view all the answers

If Asparagine is converted to Aspartate, what enzyme is utilized in this reaction?

Asparaginase Signup and view all the answers

Which of the following reactions results in the release of ammonia?

All of the above Signup and view all the answers

Study Notes

Biochemistry of GIT

This book covers the biochemistry of the Gastrointestinal Tract (GIT).
The content is divided into three main sections: Protein Metabolism, Nucleotide Metabolism, and Vitamins and Minerals.
The book is authored by Dr. Mohamed Agha for the academic years 2024-2025.

Protein Metabolism

Blood amino acid levels range from 3-6 mg/dL in the fasting state, rising to 2-3 mg/dL after a protein meal.
Approximately 300 grams of protein are broken down daily into amino acids in the body.
Amino acids participate in both anabolic (building) and catabolic (breaking down) pathways.
Anabolic pathways involve the formation of tissue proteins, plasma proteins, hemoglobin, enzymes, hormones, and non-protein nitrogenous compounds.
Catabolic pathways involve the conversion of proteins to Urea, a primary breakdown product in the liver.
Energy supply from protein is 4.1 kcal/g, only if there is a lack of carbohydrates or fats.
Nitrogen balance is the difference between total nitrogen intake (from dietary protein) and total nitrogen losses (in stools, urine and other ways).
Nitrogen equilibrium occurs when nitrogen intake matches nitrogen losses.
Positive nitrogen balance occurs if nitrogen intake surpasses losses, aiding growth, pregnancy or recovery from illness.
Negative nitrogen balance happens when intake is less than losses, usually due to starvation, illness or malnutrition causing increased losses.

General Metabolism of Proteins

The liver is the main site for removing amino groups.
Major process of amino acid breakdown involves transamination followed by oxidative deamination.
Minor process happens via oxidative deamination by D- and L-amino acid oxidase.
Amino acids undergo transamination with a-ketoglutarate to transfer and amino group forming Glutamate- this is a reversible reaction
Vitamin B6 (PLP) is required as a coenzyme during transamination.

Metabolic Fate of Carbon Skeleton of Amino Acids

The carbon skeletons of amino acids, after the removal of their amino groups, are further metabolized into intermediates in the citric acid cycle (TCA cycle). These intermediates can be converted to:
Glucogenic amino acids
Ketogenic amino acids
Mixed (glucogenic and ketogenic) amino acids

Metabolism of Ammonia

Ammonia is primarily removed from the body as urea, through the urea cycle which happens in the liver.
90% of Ammonia is converted into Urea.
60% of the urea is formed through the conversion of Glutamine and Glutamate into ammonia- then urea.

Ammonia Transport in Circulation

Ammonia is transported in the blood predominantly as non-toxic forms like urea and glutamine.
Glutamine is an amide of glutamic acid, acting as a storage and transport form for ammonia.

Krebs Urea Cycle

The Krebs Urea Cycle (Krebs Hensleit Cycle) is a metabolic process that converts ammonia into urea in the liver.
Urea is the major end product of amino acid nitrogen catabolism, making up 90% of excreted nitrogen
The Urea cycle comprises five reactions, with two happening in the mitochondria and the remaining three in the cytoplasm.
Fumarate is a link between the Krebs Urea Cycle and the Krebs TCA Cycle (Citric Acid Cycle).

Short-Term and Long-Term Regulation of Urea Cycle

The urea cycle is regulated to match the body's need for urea production.
In short-term regulation, enzymes like Carbamoyl Phosphate Synthetase I are directly affected by N-acetylglutamate, helping the rate-limiting step.
Long-term regulation manages enzyme levels based on protein intake and other factors.

Ammoniacal Encephalopathy

Elevated ammonia levels in the blood can be toxic to the brain.
This can cause a spectrum of disorders, from mental alterations to coma. This toxicity is due to the conversion to Glutamate, which in turn alters GABA production and decreases ATP synthesis.
There are both congenital and acquired reasons for these conditions.

Metabolic Disorders of Phenylalanine and Tyrosine

Phenylketonuria (PKU) is a genetic disorder affecting phenylalanine metabolism.
Tyrosinemia is another genetic disorder affecting tyrosine metabolism.

Tyrosine

Tyrosine is a non-essential amino acid synthesised from phenylalanine.
It is a precursor to several important compounds for the body.

Melanin

Melanin is a pigment synthesised from tyrosine.
Melanin protects the skin from harmful UV rays.
Melanin production is affected by a number of illnesses or disorders including disorders in amino acid metabolism

Metabolism of Glycine

Glycine is a non-essential amino acid.
It is converted into serine, then pyruvate through different steps of reaction.
It has major roles in the body including its role in protein synthesis, purine synthesis, and bile salt synthesis

Metabolism of Tryptophan

Tryptophan is a glucogenic and ketogenic amino acid, with important roles in both energy creation and structure in the body
It is an essential amino acid, converted through a specific pathway to NAD+ and NADP+
Tryptophan through the Kynurenine pathway gets converted to important cofactors which can be converted to niacin.

Water Soluble Vitamins

Vitamins like Thiamine (B1), Riboflavin (B2), Niacin (B3), and Pantothenic acid (B5) are all crucial in important energy releasing reactions.
They play major roles in the cellular reactions by helping in converting nutrients into energy.
Vitamin B6, biotin and folic acid also fulfil important functions in the body.

Mineral Metabolism

Discusses elements that play vital roles in body functions, such as:
Sodium-osmotic balance, muscle functions
Potassium-muscle tone, nerve impulses
Calcium-bone formation, blood clotting
Magnesium-enzyme activation
Phosphorus-energy storage, bone formation
Sulphur-amino acid structure
Chloride-regulation of body fluids
Other trace elements also mentioned: copper, zinc, iodine, manganese, selenium, etc

Nucleotide Metabolism

Nucleotides are vital building blocks of DNA and RNA, carrying energy and acting as coenzymes.
Their digestion involves enzymes that break down nucleoproteins, nucleic acids into nucleotides
Nucleosides are absorbed from the digestive system.
The degradation and synthesis of purine and pyrimidine nucleotides is covered.

Purine Salvage Pathway

This recycling pathway saves energy by reusing the nitrogenous bases from the breakdown of nucleotides, mainly those from purines.

Purine Catabolism

Explains the breakdown of purines, leading to the production of uric acid, the final product of this breakdown.

Clinical Disorders of Purine Catabolism

Discusses hyperuricemia and gout, conditions resulting from abnormalities in uric acid metabolism.

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Description

Test your knowledge on the urea cycle and citric acid cycle with this quiz. Explore key concepts like ATP consumption, enzyme activity, and the significance of metabolic intermediates. Perfect for biochemistry students and professionals alike.