Protein And Amino Acid Metabolism Flashcards
What is Creatinine?
A breakdown product/metabolite of Creatine and Creatine phosphate in muscle
What is the function of Creatinine?
Has no metabolic function so is excreted by the kidneys in the urine
Clinical relevance of Creatinine levels in the urine
Provides an estimate of muscle mass
Clinical relevance of creatinine plasma levels
Indicate renal function
High plasma levels and low urine levels = poor blood filtration in kidneys
What is Nitrogen (N) Balance?
When rate of nitrogen intake matches the rate of nitrogen lost
What is meant by a positive N Balance?
More nitrogen is taken in than is lost
Increase in total body protein
When is it normal to have a positive N Balance?
Growth
Pregnancy
Adult recovering from malnutrition
What is meant by a Negative N Balance?
The loss of N is greater than the intake of N
Net loss of total body protein
When is a Negative N balance normal?
It is NEVER Normal
It indicates trauma, infection or malnutrition
What is protein turnover?
The constant breakdown and re-synthesis of proteins in the body
What is a glucogenic amino acid?
An amino acid who’s carbon chain can undergo GLUCONEOGENESIS to produce glucose to release energy
What is a ketogenic amino acid?
An amino acid who’s carbon Skelton goes into produce Ketone bodies (ketogenesis) and fatty acids to release energy
Give an example of a Glucogenic amino acid
Alanine
Give an example of a Ketogenic amino acid
Leucine
Give an example of an amino acid which is both glucogenic and ketogenic
Phenylalanine
When are protein reserves used for energy?
During starvation/extreme stress
What type of molecules regulate mobilisation of protein reserves for energy?
Hormones
What hormones stimulate protein synthesis and inhibit proteolysis?
Insulin and GH
Which hormone inhibits protein synthesis and simulated proteolysis?
Glucocorticoids (Cortisol)
How does excess Cortisol lead to the purple striae in the skin in Cushing’s Syndrome?
Cortisol stimulates proteolysis
Proteins in skin broken down
Skin weakens forming striae
How are proteins metabolised?
Digested to free amino acids
Either Used to produce cellular proteins or enter the liver
Amino group removed and excreted as urea in urine
Carbon Skeleton used to produce energy, the way this occurs depends on whether the amino acid was glucogenic or ketogenic
What are the 9 essential amino acids?
Isoleucine
Lysine
Threonine
Histidine
Leucine
Methionine
Phenylalanine
Tryptophan
Valine
What are the 3 Conditionally essential amino acids?
Arginine
Tyrosine
Cysteine
Why can tyrosine be a conditionally essential amino acid?
Tyrosine can be made from Phenylalanine
If diet is low in phenylalanine Tyrosine becomes Conditionally essential
Why can cysteine be a conditionally essential amino acid?
Cysteine can be synthesised from Methionine
If diet is low in Methionine cysteine is conditionally essential
Why can arginine be a conditionally essential amino acid ?
Small amounts of arginine can be made
Becomes essential in periods of active growth like pregnancy
What are the 2 ways by which the amino group of amino acids can be removed to allow the carbon skeleton to be utilised in oxidative metabolism?
Transamination
Deamination
What happens to the nitrogen removed from an amino acid?
Incorporated into other compounds
Excreted as urea
What is transamination?
Transfer of the amino groups to another molecule
What is the name of the enzyme which allows for transamination to occur?
Aminotransferase
What are the 2 key aminotransferases?
Alanine aminotransferase (ALT)
Aspartate aminotransferase (AST)
What is the clinical significance of the levels of ALT and AST?
Part of the liver function test
Levels high in conditions that cause extensive cell necrosis
What is Deamination?
When the amino group is removed and forms free ammonia
(Normally happens in liver and kidney)
What is the fate of free ammonia?
Converted to urea which is non toxic and inert
Ammonia is very toxic
What is the purpose of the urea cycle?
Safely convert ammonia into urea for excretion in urine
Where does the urea cycle take place?
Liver
How many enzymes are involved in the urea cycle?
5
How does a high protein diet affect the levels of the 5 enzymes involved in the urea cycle?
Increases the enzyme levels since more amino acids are being taken in so more ammonia is going to be produced
How does a low protein diet affect the levels of the 5 enzymes involved in the urea cycle?
Low protein = less amino acids so less ammonia is going to be produced
Therefore the enzyme levels are reduced
How is ammonia toxic?
Readily diffusible
Causes alkaline blood
Alters blood brain barrier
Interfere with Krebs cycle
What is Phenylketonuria?
Autosomal recessive Genetic defect in amino acid metabolism, causes accumulation of phenylalanine in tissues, blood and urine
On chromosome 12
What enzyme is deficient in Phenylketonuria (PKU)?
Phenylalanine hydroxylase
What substances build up as a result of Phenylketonuria?
Phenylalanine
Phenylketones
What is not produced as a result of a phenylalanine hydroxylase deficiency in Phenylketonuria?
Tyrosine
What is the significance of being deficient in Tyrosine?
Can’t synthesise:
Adrenaline
Noradrenaline
Dopamine
Thyroid hormones
What are the symptoms of PKU?
Severe intellectual disability
Microcephaly
Seizure
How is PKU Treated?
Avoid high protein foods
Diet with low phenylalanine and high tyrosine
What is Homocystinurias?
Autosomal recessive disorder
A problem breaking down methionine causing excess homocysteine to be excreted in urine as homocystine
Homocysteine is what would be present in the plasma (homocystine is the oxidised form of homocysteine formed from methionine being metabolised)
Which enzyme is defective in Homocystinurias?
Cystathionine B-synthase
What problems does Homocystinurias cause?
Problems with:
Connective tissues
Muscles
CNS
CVS
How does deficiency of cystathionine B-synthase cause disease?
Homocysteine and it’s metabolites accumulate causing disease symptoms
