urea cycle and nitrogen metabolism Flashcards
state the functions of the urea cycle
- mainly to eliminate toxic ammonia from the body
- regulation of nitrogen balance
- maintenance of blood pH
- amino acid metabolism
- regulation of blood urea levels
state the mechanisms which operate to regulate the urea cycle
- susbtrate availibility (ammonia concentration and availibility of amino acids)
- enzyme regulation
- hormonal regulation (glucagon, insulin and cortisol stimulate or inhibit urea cycel)
- nitrogen balance and demand (less cycle activity in deman of N)
give the reactions which lead to formation of urea from NH4 and CO2 including those involved in the regenerations of aspartate
what are the three processes in the maintenance of nitrogen balance
Transamination: Transfers amino groups from amino acids to α-keto acids, producing new amino acids and α-keto acids. Key enzymes are ALT and AST.
Oxidative Deamination: Removes amino groups from glutamate, producing α-ketoglutarate and free ammonia. The key enzyme is glutamate dehydrogenase.
Direct Deamination: Directly removes amino groups from specific amino acids, producing α-keto acids or other products and free ammonia. Key enzymes include serine dehydratase and threonine dehydratase.
show how nitrogen-containing groups generated from amino acid catabolism in muscle and other tissues are transported to the liver for converstion to urea
Nitrogen-containing groups generated from amino acid catabolism in muscle and other tissues are transported to the liver primarily through two key amino acids: alanine and glutamine. These amino acids serve as carriers for ammonia (NH₃) and amine groups, safely transporting them through the bloodstream to the liver, where they are converted to urea via the urea cycle
define glucogenic when applied to amino acids
glucogenic refers to amino acids that can be converted into glucose through gluconeogenesis. These amino acids are metabolized into intermediates that can enter the citric acid cycle (Krebs cycle) and subsequently be used to produce glucose via the gluconeogenic pathway.
- pyruvate
- oxaloacetate
- alpha ketogluterate
- succinyl CoA
- fumarate
define the term ketogenic when applied to amino acid catabolism
ketogenic refers to amino acids that are degraded into acetyl-CoA or acetoacetate, which are precursors for ketone bodies. These amino acids can contribute to ketogenesis, the process of producing ketone bodies, which serve as an alternative energy source, especially during prolonged fasting, low carbohydrate intake, or intense exercise.
- leucine (keto only)
- lysine (keto only)
- isoleucine
- phenylalanine
- tyrosine
- tryptophan
- threonine
list the seven amphibolic end points of amino acid catabolism and indicate which are glucogenic and which are ketogenic
- pyruvate (glucogenic)
- oxaloacetate (glucogenic)
- alpha ketoglutarate (glucogenic)
- succinyl-CoA (glucogenic)
- Fumarate (glucogenic)
- Acetyl-CoA (ketogenic)
- Acetoacetate (ketogenic)
explain why some amino acids are both glucogenic and ketogenic
their catabolism can produce both glucogenic intermediates (which can be used to synthesize glucose) and ketogenic intermediates (which can be used to produce ketone bodies). This dual capability allows these amino acids to contribute to different metabolic pathways depending on the body’s needs
what are the Two pathways can lead to an excess of nitrogenous compounds in animals’ body:
- diet protein digestion and breakdown = amino acids
- breakdown of skeletal muscle proteins (starvation) = amino acids
what is the process of deamination
breaking down amino acids into their usable biproducts
why is the urea cycle important
- when amino acids are broken down in the body, one of the by products is ammonia
- ammonia is toxic
- ammonia can be added to other products or converted to urea via the urea cycle
- urea can then be excreted in urine
- this process mainly takes placce in the liver (but other organs are capable too)
where does ammonia come from
break down of amino acids
- intra cellular amino acid turn over
- dietary protein
where does the urea cycle occur
- ammonia is found in all cells during metabolism of various compounds
- occurs mostly in liver
- urea excreted by kidneys are urine
what happens if too much ammonia builds up
- ammonia is toxic (especially to brain)
- build up id known as hyperammonemia
- damages cells
- damages brain cells leading to abnormal behaviour, including dizziness coma and death
what conditions cause hyperammonemia
- liver dysfunction
- abnormality in hepatic portal flow (i.e shunt delivering blood away from liver)
- starvation (body breaks down skeletal muscle = more amino acid catabolism)
- abnormality in an enzyme involved in urea cycle
what is deamination
the process of removing an amino group from an amino acid or compound
what is the krebs cycle
a cyclic process by which a series of enzymes convert Acetyl-CoA into carbon dioxide (breathed out), water and energy (ATP)
- occurs in EVERY CELL
what is nitrogen balance
refers to the amount of nitrogen availible for use in the body. nitrogen is required to create and rebuild protein after it is lost (excersise). the amount of nitrogen lost should not exceed the amount availible
what are nitrogen compounds
- NH2
- NH3 (ammonia)
- NH4 (ammonium)
all amino acids contain nitrogen
what are non-protein nitrogens
nitrogens from amides, amines, urea, peptides and ammonium ions.
- ruminants can use non-protein nitrogen for protein synthesis as NPNs cn be converted into ammonia as a nitrogen source
what is oxidative deamination
the process of removing an amino group from an amino acid or compound. A result of this process creates ammonia
what is transamination
the process by which amino acids are transferred between compounds often to create a new molecule (happens in the liver)
summarize the urea cycle
amino cids are deaminated (amino acid removed from compound) creting alpha keto acids (for Krebs) and ammonia
- ammonia converted to urea
in simple stomached animals, in which organ does the majority of metabolism of ammonia take place
liver
what is the name of the process for amino acids to be modified to NH4 or alpha keto acids
transamination
what is the term for the creation of new glucose from the krebs cycle
gluconeogenesis
how do most land animals excrete urea
urea created in liver which is transported to kidneys via blood. the urea is then excreted with wter via ureters into the bladder in the form of urine. the urine is excreted
what are the main ways by which excessive amino acids can be created in the body
- excessive dietary protein
- breakdown of skeletal muscle due to starvation
what is the definition of an essential amino acid
an amino acid that cannot be synthesised by the animal and must be obtained via diet
what is the definition of a non-essential amino acid
an amino acid which can be synthesised from alpha keto precursors in the animal
what enzymes are involved in the urea cycle
- carbamoyl synthetase
- ornithine transcarbamoylase
- ATP
- arginosuccinase
- arginase
