Chapter 15 Nitrogen Metabolism 2 (degredation) Flashcards
What is meant by the term turnover of protein and nuclei acids?
The need to constantly undergo renovation of most living cells, as the cellular concentration of each type of protein is due to the balance between its synthesis and degradation it serves different purposes:
1) metabolic flexibility
2) protection us from abnormal proteins
3) regulate some metabolic processes
What are the classification of amino acids in catabolism?
1) gluconeogenic amino acids
2) ketogenic amino acids
What are the seven products yielded from all amino acid catabolism?
1) Acetyl-CoA
2) Acetoacetyl-CoA
3) Pyruvate
4) a-ketoglutarate
5) succinyl-CoA
6) Fumarate
7) Oxaloacetate
What is the meaning of glucogenic amino acid?
The amino acid that yield intermediate of gluconeogenesis upon catabolism (pyruvate, a-ketoglutarate, succinyl-CoA, fumarate, oxaloacetate), can be used in gluconeogenesis
What is meant by ketogenic amino acids?
The breakdown of amino acids producing ketone bodies (Acetyl-CoA, Acetoacetyl-CoA), they can be converted into fatty acids or ketone bodies they are:
1) leucine
2) lysine
- FYI (ANY AMINO ACID THAT STARTS WITH AN “L”)
What are the five amino acids that can be ketogenic and glucogenic?
1) isoleucine
2) phenylalanine
3) threonine
4) tryptophan
5) tyrosine
-FYI (ANY AMINO ACID THAT STARTS WITH “T OR i” + phenylalanine)
What is meant by deamination?
The removal of the amine group from an a-amino acid via two different reactions:
1) Transamination
2) Oxidative deamination
What is the characteristics of the deamination reaction?
1) Reversible (amino groups can be shifted from abundant amino acids to synthesize the rare ones)
2) When the amino groups are in excess they become available for urea synthesis, which is synthesized in large amounts when the diet is high in protein or there is a massive breakdown of protein (during starvation)
- But its not for all amino acid a-carbon (the famous one is glutamate dehydrogenase) the remaining is by the transfer of a-amino acid to an a-keto acid
What are the enzymes that can deaminase some of the amino acids?
The main one is glutamate dehydrogenase used in the oxidative deamination of glutamate the rest are:
1) L-amino acid oxidases
2) Serine & threonine dehydrases
3) Bacterial urease (intestinal bacteria)
4) Adenosine delaminase
How does different organs get rid of excess amino group?
1) Muscles: amino groups are transferred to a-ketoglutarate forming glutamate & a-keto acids (which is transferred by the blood to the liver by the glucose-alanine cycle)
2) Liver: reverse of the alanine transaminase reaction forms the glutamate
How are the ammonium ions produced by extrahepatic tissues arrived into the liver?
As the amide group of glutamine
How is glutamine synthesized?
By the conversion of glutamate via glutamine synthetase using ATP into glutamine, in the liver it is hydrolyzed to form glutamate and NH4+ (using glutaminase), and an additional NH4+ is formed by the conversion of glutamate into a-ketoglutarate via glutamate dehydrogenase
What forms urea?
1) ammonia
2) CO2
3) Aspartate
What is the percentage of nitrogen is disposed by the urea cycle?
90%
What are the reactions of the urea cycle?
Mainly in the liver occurring in both the mitochondria and the cytoplasm
1) CO2 + ammonia = carbamoyl phosphate via carbamoyl phosphate synthetase I utilizing 2ATP into 2ADP (it is the regulatory step of the urea cycle)
2) carbamoyl phosphate + L-ornithine = L-citrulline + Pi via ornithine transcarbamoylase
Citrulline will leave the mitochondria for an exchange with L-ornithine
3) L-citrulline + Aspartate = Arginosuccinate utilizing ATP into AMP + PPi via the enzyme arginosuccinate synthase
4) arginosuccinate lyase will cleave fumarate forming arginine
5) arginase will utilize H2O cleaving Urea producing ornithine
What is the overall equation of the urea cycle?
CO2 + NH4+ + Aspartate + 3 ATP + 2 H2O = Urea + Fumarate + 2 ADP + 2Pi + AMP + PPi + 5H+
What is the structure of urea?
NH2-C-(=O)-NH2
It can hold two ammonium ions, one of them is from free ammonia the other one is from aspartate
What is the aspartate-arginino succinate shunt of citric acid cycle?
It connects the fumarate produced n the urea cycle to the citric acid cycle via some of the isoforms of the enzymes found in the mitochondria which converts fumarate into malate and malate into oxaloacetate which will be converted into aspartate by the transamination of a-amino acid (usually glutamate) into its a-keto acid
How is the urea cycle controlled (regulated)?
- Urea is strictly regulated as it is toxic to the body
- Dietary protein regulate urea cycle enzymes
- Glucagon and glucocorticoids activates urea cycle
- Insulin represses its synthesis
- Substrates concentration controls all enzymes function
The short term regulation is by the control of the enzymes, while the long term regulation is by the variation in the dietary protein consumption
Examples of the catabolism of amino acid carbon skeleton
1) Asparagine converted to aspartate converted to oxaloacetate which can be used for energy production or glucose biosynthesis
2) glutamine converted to glutamate converted to a-keto glutarate which can be used in glucose biosynthesis or energy production
3) alanine to pyruvate which can be used for glucose biosynthesis, energy production, fatty acids, cholesterol
What are the amino acids converted into pyruvate?
1) alanine
2) serine
3) glycine
4) cysteine
5) threonine
What are the amino acids that can be converted into acetyl-CoA?
1) pyruvate
2) isoleucine
What are the amino acids that can be converted into acetoacetyl-CoA?
1) phenylalanine
2) tyrosine
3) tryptophan
What are the amino acids that can be converted into citric acid cycle intermediate?
1) Forming a-ketoglutarate (1. Glutamate (glutamine), 2. Arginine, 3. Proline, 4. Histidine)
2) Forming succinyl-CoA (1. Methionine, 2. Threonine, 3. Isoleucine, 4. Valine)
3) Forming oxaloacetate (Aspartate)
