Nitrogen 2 Flashcards
What is the fate of nitrogen in aquatic vertebrates?
-Ammonia released to environment via passive diffusion from epithelial cells or active transport via gills
What is the fate of nitrogen in terrestrial vertebrates and sharks?
-Nitrogen excreted in the form of urea as urea is less toxic than ammonia and is highly soluble
What is the fate of nitrogen in birds/reptiles?
- Excrete nitrogen as uric acid.
- Excretion as paste as uric acid is insoluble which allows for conservation of water
What do humans and apes excrete nitrogen as?
- Urea from amino acids
- Uric acid from purines
In what form is ammonia safely transported in the bloodstream?
Glutamine
Where is excess glutamine processed?
- Intestines
- Kidneys
- Liver
What do vigourously working muscles rely on for energy?
Anaerobic process of glycolysis
What does glycolysis yield?
Pyruvate which cannot be metabolised anaerobically and often builds up as lactic acid
How can pyruvate be converted to alanine?
Glutamate can donate ammonia to pyruvate to make alanine for transport to the liver
What is the glucose-alanine cycle?
- Proteins broken down when exercising
- Transported to liver as alanine/glutamine
- Carbon skeleton toe pyruvate
- Nitrogen is excreted as ammonia and converted to urea by the urea cycle
Why does glutamate have to be changed to alanine/glutamine to be transported to the liver?
- Glutamate has a negative charge
- Alanine/glutamine have NO charge
- Charged molecules don’t pass through membranes easily hence converted to uncharged molecule to allow for easy transport
What happens to excess glutamate?
It is metabolised in the mitochondria of hepatocytes
What is the glutamate dehydrogenase reaction?
Two-electron oxidation of glutamate followed by hydrolysis
What is the net process of the glutamate dehydrogenase reaction?
Oxidative deamination of glutamate
Where does the glutamate dehydrogenase reaction occur?
In mitochondrial matrix of mammals
What can used as the electron acceptor in the glutamate dehydrogenase reaction?
NAD or NADP
How is ammonia re-captured?
Via the synthesis of carbamoyl phosphate
What is the first nitrogen- acquiring reaction?
Recapturing of ammonia
What is the second nitrogen acquiring reaction?
Entry of aspartate into the urea cycle
What happens to the nitrogen from carbomoyl phosphate?
It enters the urea cycle
What happens to carbon atoms of degraded amino acids?
They emerge as major metabolic intermediates
What happens to the carbon skeletons after amino groups are removed?
Either converted to glucose or oxidised as part of the citric acid cycle
What are the 6 intermediate compounds?
- Acetyl-CoA
- Pyruvate
- a-ketoglutarate
- Succinyl-CoA
- Fumarate
- Oxaloacetate
What is the primary role of carbs and fat?
To provide energy
What is the primary role of amino acids?
Building blocks for proteins
What are the 8 essential amino acids?
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenlyalanine
- Threonine
- Tryptophan
- Valine
Glucogenic
Amino acids which feed in to gluconeogenesis and go on to produce glucose or glycogen in the liver
Ketogenic
Amino acids which feed in to acetoacetate or acetyl CoA but cannot result in gluconeogenesis
What amino acids are both glucogenic and ketogenic?
- Isoleucine
- Tyrosine
- Phenylalanine
Why can ketogenic amino acids not result in gluconeogenesis?
Pyruvate dehydrogenase reaction is irreversible and no NET synthesis of oxaloacetate through citric acid cycle
What are ketone bodies?
- Small water soluble
- Produced by liver
- Used by brain in absence of glucose
