Protein and Amino Acid Metabolism Flashcards
what are the major nitrogen containing components in the body
- amino acids
- proteins
- nitrogenous bases
- creatine
what is creatinine
break down product of creatine and creatine phosphate
what is the level of creatinine in the urine proportional to
muscle mass
what is creatinine used as an indicator for
renal function (raised levels on damage to nephrons)
when is it normal to have a large nitrogen intake than output
during pregnancy or rapid growth
when is it normal to have a larger nitrogen output than intake
it is never normal - only occurs in trauma, infection and malnutrition
what is the main method for nitrogen output
loss of nitrogen through the faeces and urine
what is proteolysis
production of amino acids from proteins
what happens to amino acids in the liver
they are broken down into an amino group and the carbon skeleton
what are glucogenic amino acids
ones that can undergo gluconeogenesis to give energy e.g. glycine
what are ketogenic amino acids
ones that produce ketone bodies to give energy e.g. lysine and leucine
what determines whether an amino acid is glucogenic or ketogenic
their side chains
give an example of an amino acid that is both glucogenic and ketogenic
tyrosine
what effect does insulin have on protein synthesis
increases
what affect does glucocorticoids have on protein synthesis
decreases it
what is cushing’s syndrome
excessive breakdown of protein occurs weakening the skin structure leading to striae formation
what are non essential amino acids synthesised from
- intermediates of glycolysis
- pentose phosphate pathway
- krebs cycle
what is transamination
the conversion on one amino acid to another by swapping an amine group of an amino acid with an oxygen of a keto acid
what does tyrosine produce
- catecholamines
- melanin
- thyroid hormones
what does cysteine produce
- glutathione
what does histidine produce
histamine
what does arginine produce
nitric oxide
what does glycine produce
- haem
- creatine
- purines
- glutathiones
what are the 2 methods for removal of nitrogen from amino acids
- transamination
- deamination
outline transamination to produce glutamate
alpha ketogluatarate is converted into glutamate and an amino acid into a keto acid by an aminotransferase enzyme
outline transamination to produce aspartate
a glutamate is converted into a keto acid and oxaloacetate is converted into aspartate by aspartate aminotransferase
what coenzymes do aminotransferase enzymes use
coenzymes requiring vitamin B6
what does alanine aminotransferase do
converts alanine to glutamate
what can levels of aminotransferase enzymes be used to test
liver function tests
what do high levels of aminotransferase enzymes mean
liver cellular necrosis from toxins, viral hepatitis
what is deamination
the removal of amine group from an amino acid
where does deamination occur
liver and kidney
why must ammonia be removed
it is very toxic
what enzymes deaminate amino acids
- amino acid oxidases
- glutaminase
- glutamate dehydrogenase
what happens to ammonia
it is converted to urea
why is ammonia converted to urea
urea is non toxic, water soluble, inert and excreted in the urine
outline the urea cycle
ammonia combines with carbon dioxide. the product combines with aspartate or glutamate which then eventually produces urea
how many enzymes are involved in the urea cycle
5
what induces the urea cycle enzyme levels
high protein diet
what is refeeding syndrome
when malnourished patients have a downregulation of enzymes in the urea cycle and so giving them too much protein quickly increases ammonia toxicity
what do defects in the urea cycle enzymes lead to
hyperammonaemia
accumulation of urea cycle intermediates
how do you manage having defects in the urea cycle
- low protein diet
- replace amino acids with keto acids in diet
what are symptoms of urea cycle defects
- vomiting
- seizures
- coma
- irritability
- mental retardation
how is ammonia toxic
- can alter the BBB and be toxic to the brain
- interferes protein synthesis
- affects pH
- interferes TCA cycle
at what levels should blood levels of ammonia be
25-40 micro moles
how is ammonia disposed (2)
- combined with glutamate to form glutamine which is transporter to the liver or kidneys where its cleaved by glutaminase to reform glutamate and ammonia, which is fed into the urea cycle
- combined with pyruvate to form alanine which is transported to the liver where its converted back into pyruvate by transamination and the amino group if fed into the urea cycle
why is the heel prick test carried out
to screen blood for sickle cell, cystic fibrosis and amino acid metabolism defects (e.g. PKU and Homocystinuria)
what is PKU
deficiency in phenylalanine hydroxylase causing the accumulation of phenylalanine which produces phenylketones
what are the symptoms of PKU
- intellectual disability
- seizures
- developmental delay
hypopigmentation
what do phenylalanine hydroxylase catalyse
conversion of phenylalanine into tyrosine
what is homocystinurias
problems with breaking down methionine giving excess homocysteine due to defects in cystathionine beta synthase
what are the treatments for PKU
- controlled low phenyalalanine diet
- avoid artificial sweeteners
- avoid high protein foods
what are the treatments for Homocystinurias
- low methionine diet
- avoid milk, meat, eggs, cheese
- cysteine, Vit B6 supplement
why should people with homocystinurias take Vit B6 supplemements
as cystathionine requires Vit B6 as a co factor
what cant be produced in homocystinurias
cysteine
what does homocystinurias cause
cardiovascular disease
- affects CT, muscle, CNS and CVS
