Amino Acid Catabolism Flashcards
In uncontrolled diabetes, or a tumor, what is the energy source?
- Glucose cannot be used efficiently
- Fat and, if not available, protein will be degraded
Where are most amino acids metabolized?
In the liver
What happens to the ammonia? What happens to the carbon skeleton?
- Ammonia: recycled or excreted
- Carbon skeleton: TCA cycle, gluconeogenesis, ketogenesis
What happens to proteins in the stomach?
- Gastrin –> HCl
- Pepsinogen –> pepsin: protein degradation
What happens to proteins in the duodenum?
- Acidity stimulatse secretin, which stimulates the pancreas to produce bicarbonate
- pH rises to 7
What does the pancreas secrete for protein degradation?
Trypsin and chymotrypsin
What is the general amino acceptor?
a-ketoglutarate
Aminotransferases are _____ specific
amino acid
What happens when a-ketoglutarate accepts an amino group? What is the amino acid that lost its amino group known as?
- Glutamate
- a-Keto acid
PLP uses _______ as a cofactor in transamination reactions
Vitamin B6
Vitamin B6 is a cofactor for _____ and ______
PLP
glycogen phosphorylase
What happens in the liver in deamination reactions?
- Glutamate dehydrogenase removes the amino group from glutamate
- Re-creates a-ketoglutarate
Where does deamination occur?
Mitochondria of liver cells
What is the role of glutamine synthase?
- Uses energy to incorporate ammonia, and forms glutamine
- Glutamine is excreted into circulation
What is the role of glutaminase?
- Once glutamine is incorporated into the liver mitochondria
- Converts glutamine to glutamate, which removes the ammonia that is then excreted as urea
Pyruvate accepts an amino group from _____ to form _____
glutamate
alanine
In the liver, alanine is degraded by removing an ______ to form ______
amino
pyruvate
Pyruvate undergoes ________ to produce glucose
gluconeogenesis
What are the steps to the glucose-alanine cycle?
- Glucose –> Pyruvate
- Pyruvate + Amino group from Glutamate –> Alanine
- Liver: Alanine – amino group –> Pyruvate
- Pyruvate –> gluconeogenesis = glucose
- Glucose can be used for exercise
What are the sources of ammonia that contribute to glutamate in the mitochondria?
- Glutamine
- Alanine
- Glutamate
Glutamate can donate its amino group to form what? How many ammonias does that produce?
- a-Ketoglutarate
- 1 ammonia
Glutamine can donate its amino group to form what? How many ammonias does that produce
- Glutamate, which can donate its amino group to form a-Ketoglutarate
- So, 2 ammonias total
Ammonia from the intestines arrives to the liver, and is combined with ____ to form ______ through the enzyme ___________, which utilizes ____ ATPs
HCO3
carbonoyl phosphate
carbonoyl phosphate synthetase 1
2
Oxaloacetate uses the amino group from __________ to form __________, with the enzyme ___________
glutamate
aspartate
Aspartate amino transferase
_____, like Glutamate, is an amino group donor
Aspartate
What are the four cytosolic enzymes of the urea cycle?
- Ornithine transcarbamylase
- Arginosuccinate synthase
- Arginosuccinase
- Arginase
How is citrilline synthesized? What enzyme? Where does it travel to?
- Enzyme: Ornithine transcarbamylase
- Combining carbonyl-phosphate and ornithine
- Travels to the cytosol
How is arginosuccinate synthesized? What enzyme?
- Enzyme: Arginosuccinate synthase
- Citrilline and aspartate are combined
How is arginine formed in the urea cycle? What enzyme?
- Enzyme: Arginosuccinase
- Fumarase is discarded from arginosuccinate, to form arginine
How is ornithine synthesized in the urea cycle? Where does it travel to?
- Enzyme: Arginase
- Urea is removed from arginine to synthesize ornithine, which travels to the mitochondria
Which enzymes of the TCA cycle contain both cytosolic and mitochondrial isoforms?
- Fumarase
- Malate dehydrogenase
Which intermediate of the TCA cycle contributes to the formation of Aspartate?
Oxaloacetate
Which intermediates link the TCA cycle and the urea cycle?
- Oxaloacetate
- Fumarate
- Aspartate
- Malate
What is the carbon skeleton converted to during amino acid catabolism?
Intermediates of the TCA cycle
What do glucogenic amino acids create? What can that be incorporated into?
- Pyruvate
- Can be incorporated into gluconeogenesis
What do ketogenic amino acids create?
- Acetyl-CoA
- Intermediates of ketone body synthesis
Which amino acids are both ketogenic and glucogenic?
- Isoleucine
- Phenylalanine
- Threonine
- Tryptophan
- Tyrosine
Which amino acids are exclusively ketogenic?
Lysine and Leucine
Which amino acids are ketogenic?
- Leucine
- Lysine
- Phenylalanine
- Tryptophan
- Tyrosine
- Isoleucine
- Threonine
What is glutamate dehydrogenase activated by?
ADP
What is glutamate dehydrogenase inhibited by?
GTP
What are the 4 enzymes of the urea cycle and carbamoyl phosphate synthase 1 regulated by?
Nutritional status
What happens to the enzymes of the urea cycle when an individual is starving?
Enzymes are increased since you are metabolizing more amino acids
What happens to the enzymes of the urea cycle when an individual is consuming a protein-rich diet?
- Surplus amino acids = more ammonia produced
- Enzymes are upregulated
What is the high-energy used by the urea cycle offset by?
By the NADH (2.5 ATP) malate-oxaloacetate conversion reaction
How many ATPs are utilized in the urea cycle? At which stage(s)?
- 3 ATPs are utilized in the urea cycle
- 2 ATP at carbamoyl phosphate
- 1 ATP at the stage of secondary reaction
