Nitrogen Flashcards
What are the main nitrogen containing molecules of the body?
Amino acids
Nucleotides
What is the role of dietary protein in overall nitrogen metabolism?
Primary role of carbs and fats - to provide energy
Primary role of amino acids - building blocks for proteins
How many essential and non-essential amino acids exist?
E 9
NE 20
Why do vegetarians need a variety of different plant foods to ensure adequete intake of essential amino acids?
Plant proteins are not as well digested and processed by the body as animal proteins, and are not as ‘complete’ as protein from meat.
What can cellular proteins be targeted for?
Destruction
What can cellular proteins be used for?
- Misfolded proteins
- Foreign proteins
- Unwanted proteins
Eventually all proteins are
Turned over
What is a ubiquinated protein?
Covalently modified protein to fit into the proteosome which is effectively a protein destroying machine.
What is a carbon skeleton?
The pattern in which the carbon atoms are bonded together in a molecule
Where can the aminopeptidases be found?
Intestine - membrane bound proteins
How are dietary proteins enzymatically hydrolyzed?
Pepsin cuts proteins into peptides in the stomach
Pepsin and chymotrypsin cut proteins into smaller peptides in the small intestine
Aminopeptidase and carboxypeptidase degrade peptides in the small intestine to amino acids
Under which three circumstances do amino acids go under oxidative catabolism?
Leftover amino acids from normal protein turnover
Excess dietary amino acids
Proteins in the body are broken down (during starvation)
How much of a herbivores energy intake is met by amino acids?
Small fraction
What is the name given to nitrogen fixing bacteria?
Diazotrophs
What does the assimilation stage of the nitrogen cycle consist of?
Fixation (n2 to ammonium)
TO
Glutamate
TO
other amino acids
TO
Proteins and other amino acids
What is the degradation stage of the nitrogen cycle?
Proteins/nucleotides
TO
Other amino acids
TO
Glutamate
TO
NH4+
What is the effect of lightning on nitrogen gas?
Breaks the triple bond and makes NO(nitric oxide) or NO2 (nitrite)
What ways of fixing nitrogen exist?
Haber process, Lightning, Nitrogen fixing bacteria
Name two nitrogen fixing bacteria
Cyanobacteria and rhizobia
What do the nitrogen fixing bacteria require?
Lots of ATP, nitrogenase enzyme inhibited by oxygen - anaerobic conditions needed , cyanobacteria form heterocysts whose cell wall forms a wall to oxygen, leguminous plants contain legheomoglobin which binds to oxygen and provides an environment that nitrogenase can work.
What happens to ammonium once it is fixed?
Nitrifiction to nitrite (NO2-) to nitrate (NO3-) this is taken up by plants and microbes - then converted to ammonia via nitrile
What amino acid plays a key role in regards to nitrogen?
Glutamate
What is special about glutamate?
It is the only amino acid that can directly obtain its nitrogen from NH4 and the only one that can give up its nitrogen directly
What are the 4 amino acids usually found in much higher concentrations than others?
Alanine, glutamine, glutamate and aspartate
How do organisms conserve N2?
Transamination - The transfer of amino groups from one biological molecule to another
What type of reaction is transamination if the reaction is reversible?
Synthesis and degradation
What do amino transferases rely on?
Pyridoxal phosphate cofactor transfers the amino acid during the reaction.
What molecule usually accepts the amino groups?
Alpha ketoglutarate
Which molecule usually acts as a temporary storage of nitrogen?
L - Glutamine (possible of donating the amino acid when it is needed for biosynthesis)
What is pyridoxal phosphate made from?
Made from vitamin B6
Why do all excess amino acids have to be catabolised?
There is no storage facility for protein
How is ammonia transported in the bloodstream?
As glutamine
Where is excess glutamine processed?
Intestines kidney and liver
Glutamate + ammonia =
Glutamine
How is alanine made?
Glutamate donates ammonia to pyruvate
Why is pyruvate converted to alanine?
Pyruvate builds up in an anaerobically working muscle - lactic acid build up.
By forming alanine it can be transported to the liver.
What happens to the protein that’s broken down during exercise?
Transported to the liver as alanine or glutamine.
Carbon skeleton is converted into glucose or oxidised as part of the citric acid cycle.
Nitrogen is excreted as ammonia and converted to urea by the urea cycle
Why is nitrogen transported through the body as glutamine and alanine instead of glutamate?
Glutamate has a negative charge - does not pass readily through cell membranes
Alanine and glutamine do not bear charge
Where is excess glutamate metabolised?
Mitochondria of hepatocytes
What is the name of the process where glutamate loses its notrogen as ammoia to form alpha ketoglutarate? And what is the electron acceptor?
Oxidative deamination (two electron oxidation followed by hydrolysis) NAD+ and NADP+
What is the function of Carbomyl Phosphate?
Recaptures the ammonia from glutamate and enters the urea cycle.
What is the fate of ketogenic amino acids?
They are broken down to produce acetyl - CoA (forms ketone bodies or is oxidised in the citric acid cylce) and acetoacetylacetate.
What are glucogenic amino acids?
Feed in to gluconeogenesis and can produce glucose or glycogen in the liver.
Why can’t ketogenic amino acids produce glucose?
Pyruvate dehydrogenase reaction is irreversible (Pyruvate to acetyl CoA). No net increase in Oxaloacetate.
Why can’t ketogenic amino acids produce glucose?
Pyruvate dehydrogenase reaction is irreversible (Pyruvate to acetyl CoA). No net increase in Oxaloacetate.
What do all amino transferases rely on?
Pyridoxal phosphate cofactor
Inherited metabolic disorders usually result in abnormal synthesis and catabolism of:
Amino acids
Proteins
Carbohydrates
Lipids
When are symptoms of an inherited metabolic disorder usually most severe?
Infancy or childhood
What type of inheritance pattern do IMD’s follow?
Autosomal recessive inheritance
What are some of the most common clinical features of inherited metabolic disorders present in childhood?
Acidosis
Failure to thrive
Vomiting, refusal of feeds, vomiting
Central nervous system dysfunction
Hypoglycaemia
Unusual odor
What happens to ingested protein that is surplus to the bodies needs? Why?
It is catabolised because there is no storage facility for excess proteins.
What is the urea cycle function?
Converts excess ammonia into urea in the mitochondria of liver cells.
The urea forms, then enters the blood stream, is filtered by the kidneys and is ultimately excreted in the urine.
What happens to ingested protein that is surplus to the bodies needs? Why?
It is catabolised because there is no storage facility for excess proteins.
Where in the cell is the urea cycle?
It is split between the cytosol and the mitochondria
How many enzymes catalyse the reaction in the liver?
5
What does the concentration of the enzymes controlling the urea cycle depend on?
The quantity of protein in the diet
What is the regulatory enzyme in the urea cycle?
CPS1 - Carbomyl Phosphate synthase
What is the allosteric activator of CPS1? (Carbomyl phosphate synthase)
N Acetylglutamtae
How many inherited disorders of the urea cycle exist?
6
What may amino acids be metabolised into?
Other amino acids, hormones, neurotransmitters, pigments
What do inherited gene defects in the amino acid conversion pathway result in?
Decreased enzyme activity
Decreased product
Increased precursors
Alternative metabolic products, potentially toxic
What enzyme is deficient or absent in phenylketonuria?
Phenylalanine hydroxylase (responsible for converting phenylalanine to tyrosine)
What type of inheritance is PKU?
Autosomal recessive
Why are high levels of phenylalanine bad?
Toxic - can result in impaired brain development
What is the treatment?
Reduced protein diet supplemented with tyrosine
Defects of the urea cycle can lead to
- Rare group of inherited metabolic disorders
- 6 inherited disorders of the urea cycle
- Most common is ornithine transcarbamoylase (OTC) deficiency - 1 in 40,000 UK births
- OTC has X-linked inheritance, rest are autosomal recessive
- Characterised by hyperammonaemia (elevated blood ammonia level) - high toxic
- Elevated blood ammonia is a medical emergency
- Typically presents in newborn period
Where does the urea cycle take place?
Mainly in the liver
What comprises the synthesis of urea from ammonium?
Comprises the synthesis
of urea from ammonium, CO2,
aspartate and bicarbonate.
Net reaction per urea cycle
2 NH3 + CO2 + 3 ATP + H2O → urea + 2 ADP + 4 Pi + AMP
What enters the urea cycle?
Ammonia
What leaves the urea cycle?
The urea cycle removes ammonia from the blood and makes urea, which is eventually excreted as urine.
What causes pKU
Amino acid phenylalanine to builds up in the body.
PKU is caused by a change in the phenylalanine hydroxylase (PAH) gene.
This gene helps create the enzyme needed to break down phenylalanine.
How is nitrogen transported to the liver?
The alanine-glucose cycle
Ammonia from amino acid degradation is transaminated to form glutamate.
