Protein And Amino Acid Metabolism Flashcards
(26 cards)
What is the breakdown product of creatine and creatine phosphate? In which tissue are they broken down?
Broken down into creatinine in the muscle tissue. Rate of breakdown is dependant on muscle mass (and muscle wastage)
- creatinine urine excretion over 24hrs is proportional to muscle mass
What are creatinine levels an indicator of?
Renal function - raised plasma and low urine level upon damage to kidney nephrons
What is a positive N balance?
Nitrogen intake > nitrogen output
Increase in total body protein - normal state in growth, pregnancy or in adult recovering from malnutrition
What is a negative N balance?
Nitrogen intake < nitrogen output
Net loss of body protein - never normal - trauma, infection or malnutrition
Give an example of a glucogenic amino acid
Alanine
Give an example of a ketogenic amino acid
Lysine
Give an example of an amino acid which is both glucogenic and ketogenic
Threonine
What 2 hormones increase protein synthesis and decrease protein degradation?
Insulin and Growth hormone
What group of hormones decrease protein synthesis and increase protein degradation?
Glucocorticoids e.g. cortisol
What are the 9 essential amino acids
Isoleucine, lysine, threonine, histidine, leucine, methionine, phenylalanine, tryptophan, valine
Why are animal proteins considered of higher quality than plant proteins?
Animal proteins contain all essential amino acids, most plant proteins are deficient in one or more essential amino acids
Which amino acid contains a sulfhydride group necessary to form disulphide bonds?
Cysteine
What are the 2 pathways that facilitate removal of nitrogen from amino acids?
Transamination and Deamination
Describe the mechanism of Transamination
The amine group of the amino acid is transferred to a keto acid via an aminotransferase (all aminotransferases require coenzyme pyridoxal phosphate - a vitamin B6 derivative)
What is the function of ALT?
Catalyses interconversion of alanine and alphaketoglutarate to pyruvate and glutamate
What is the function of AST?
Catalyses interconversion of aspartame and alphaketoglutarate to oxaloacetate and glutamate
What are ALT and AST levels (in a blood test) an indicator of?
Liver function - high levels found in conditions that cause extensive cellular necrosis.
E.g. viral hepatitis, autoimmune liver disease, toxic injury
What is deamination? Where does most deamination happen?
Deamination is the liberation of the amino group (of an amino acid) as free ammonia.
Most of it happens in the live and kidney
Why are ammonia and ammonium ions converted to urea?
Ammonia and NH4+ are very toxic. Urea is inert and non-toxic.
Urea is mostly excreted in urine via kidneys and performs a useful osmotic role in kidney tubes
Why can a malnourished person not be given a normal diet immediately?
Can result in refeeding syndrome
What happens in genetic disorders caused by deficiency of one of the enzymes in the urea cycle?
Hyperammonaemia and accumulation/excretion of urea cycle intermediates
Requires a low protein diet.
Symptoms include vomiting, lethargy, irritability, mental retardation, seizures, coma
Why is ammonia so toxic?
It is readily diffusible and very toxic to the brain. It interferes with amino acid transport and protein synthesis, disruption of cerebral blood flow, alkalinic pH effect, interference with metabolism of excitatory amino acid neurotransmitters, alteration of the blood-brain barrier, interference with the TCA cycle (reacts with alphaketoglutarate to form glutamate)
What are the effects of a deficiency in phenylalanine hydroxylase? What is the treatment?
Causes phenylketonuria - accumulation of phenylalanine in tissue, plasma and urine. Phenylketones in urine
Treatment is a low phenylalanine diet enriched with tyrosine, avoiding artificial sweeteners, avoiding high protein foods e.g. meat, milk, eggs
What are the symptoms of phenylketonuria (PKU)?
If not detected early, can result in: severe intellectual disability, developmental delay, microcephaly, seizures, hypopigmentation
