Amino acid catabolism Flashcards
What additional transport proteins are needed for mitochondrial uptake of L-ornithine?
NH4+, HCO3-, L-citrulline
These transport proteins facilitate the transport of these substances into and out of the mitochondria.
What happens to proteins tagged for degradation?
They are recognised by specific proteases and degraded, releasing ubiquitin for reuse.
What is the role of E3 in the ubiquitin pathway?
Catalyses the transfer of ubiquitin from E2-ubiquitin to the target protein.
What are destabilising residues in proteins?
Phenylalanine, tryptophan, aspartate, arginine, lysine.
What are stabilising residues in proteins?
Methionine, glycine, alanine, serine.
What is the substrate for E3 in the ubiquitin pathway?
E2-ubiquitin combination.
What is the function of the PEST region in proteins?
Recognised by proteolytic enzymes for degradation.
What is the primary process for protein breakdown?
Proteolysis.
What are the two types of peptidases found in the gut?
Endopeptidases, exopeptidases.
What are the key ‘thematic reactions’ in amino acid metabolism?
Transamination, oxidative deamination.
What is the main goal of catabolic transamination?
To channel amino nitrogen into a small number of amino acids.
How many essential amino acids are there?
Nine.
What is the fate of pyruvate during amino acid breakdown?
It can form glucose via gluconeogenesis.
What are glucogenic amino acids?
Amino acids that can supply gluconeogenesis.
What are ketogenic amino acids?
Amino acids that can contribute to fatty acid or ketone body synthesis.
What is the role of the Urea Cycle?
Converts toxic ammonia to urea in the liver.
What are the two processes involved in protein degradation?
Endocytosis, autophagy.
What is the energy cost to form one molecule of urea?
4 high energy phosphates (3 ATP + 1 PPi).
What types of proteins are degraded by the lysosomal pathway?
Long-lived proteins.
What is oxidative deamination?
The release of the amino group from glutamate as ammonia.
What is the significance of alanine in amino acid transport?
It transports ammonia from muscle to liver.
What is the function of glutamine synthase?
Traps ammonia by forming glutamine.
What are the five enzymes involved in the Urea Cycle?
Argininosuccinate synthase, arginase, argininosuccinate lyase, ornithine transcarbamoylase, carbamoylphosphate synthase.
What is the main source of amino acids for catabolism?
Dietary proteins, storage proteins, metabolic turnover of endogenous proteins.
What are aminotransferases also known as?
Transaminases.
What is the primary function of aminotransferases?
Catalyse the transfer of the amino group from an amino acid to a keto acid.
What is the relationship between α-oxoglutarate and glutamate?
α-oxoglutarate is converted to glutamate via transamination.
What is the breakdown product of dietary proteins?
Amino acids and small peptides.
What happens to ammonia in terrestrial animals?
It is converted to urea, a non-toxic form.
What is the difference between essential and non-essential amino acids?
Essential cannot be synthesized by the body; non-essential can.
What is the significance of histidine and arginine during cell growth?
They are essential during periods of rapid cell growth, such as childhood and illness.
What is the role of the inner mitochondrial membrane?
It is an effective barrier to charged, polar, and large molecules.
What are ammonotelic organisms?
Aquatic organisms that excrete ammonia as the major end-product of nitrogen metabolism.
Fill in the blank: The Urea Cycle is a unique function of the _____ in mammals.
liver.
What is the main aim of catabolic transamination?
To channel the amino nitrogen into a small number of amino acids, including glutamate
Where is urea produced in mammals?
In the liver through the action of the Urea Cycle
Who originally described the Urea Cycle?
Krebs and Henseleit
What are the two major routes of deamination?
- Transamination
- Oxidative deamination
What do endopeptidases do?
Hydrolyse internal peptide bonds
What do exopeptidases do?
Remove successive amino acids from the end of the peptides
What are the two types of exopeptidases?
- Carboxypeptidases
- Aminopeptidases
Does transamination result in net deamination?
No
What is the reason transamination does not result in net deamination?
One amino acid is replaced by another amino acid
What must be considered in human metabolism regarding amino acids?
The breakdown of all amino acids, not just the non-essential ones
What begins the degradation of most amino acids?
The removal of the α-amino nitrogen (–NH2 or –NH3+)
Each amino acid is broken down by a specific pathway that converges to give common metabolic intermediates. Name some of these intermediates.
- Pyruvate
- Oxaloacetate
- α-Oxoglutarate
- Acetyl CoA
- Succinyl CoA
