Proteins Flashcards
What is creatinine?
A breakdown product of creatine and creatine phosphate which is usually produced at a constant rate.
What is the creatinine urine excretion proportional to?
Muscle mass
What is a positive nitrogen balance and when is this normal?
Intake of nitrogen exceeds output therefore there is an increase in total body protein.
Normal during growth, pregnancy or in an adult recovering from malnutrition.
What is a negative nitrogen balance?
The intake of nitrogen is less then the output of nitrogen therefore there is a net loss of body protein.
This is never normal.
What can cause a negative N balance?
trauma, infection and malnutrition
What does the protein turnover refer to?
Proteins are constantly being synthesised and broken down
Name the 2 ketogenic amino acids
Lysine and leucine
Give 2 examples of amino acids that are keto and glucogenic
Tyrosine
Phenylalanine
How does cortisol affect proteins?
Increases degradation and decreases synthesis
Name the nitrogen containing compounds of the body
amino acids, proteins, purines and pyrimidine, haem, creatine, neurotransmitters, catecholamine hormones
What happens to protein in skin in Cushing’s syndrome?
Excess cortisol leads to increased breakdown of protein. This weakens skin structure and causes striae to form.
Which amino acids are essential to children and pregnant women on top of the 9 already essential amino acids?
arginine, tyrosine and cysteine
Where do the carbon atoms for the synthesis of amino acids come from?
intermediates of glycolysis, pentose phosphate pathway and the Krebs cycle
Which molecules are synthesised using tyrosine?
catecholamines, melanin, thyroid hormones, dopamine
What is arginine needed for?
Nitric oxide synthesis which is required for vasodilation
What do we require glycine to make?
purines, haem, creatine, glutathione
What kind of enzymes are used for transamination?
aminotransferase enzymes
The cofactor for the aminotransferase enzymes is a derivative of which vitamin?
Vitamin B6
Which amino acids can be fed into the urea cycle?
Glutamate
Aspartate
Which is the role of alanine aminotransferase?
Conversion of alanine to glutamate using alpha-ketoglutarate.
What is the role of aspartate aminotransferase?
To convert glutamate to aspartate using oxaloacetate.
What do we measure as part of a liver function test?
ALT and AST levels in the plasma
When are AST and ALT levels high?
When the functioning of the liver is problematic
What are the deamination enzymes?
amino acid oxidases, glutaminase and glutamate dehydrogenase
What are the features of urea?
high nitrogen content, water soluble, chemically inert, non-toxic
Where does the urea cycle occur?
mitochondria and cytoplasm of hepatocytes
What other molecules does the urea cycle require?
carbon dioxide
water
Does the urea cycle require energy?
Yes
How many enzymes are involved in the urea cycle?
5 enzymes
Which inheritance pattern do defects in the urea cycle follow?
Autosomal recessive
What does a deficiency in one of the enzymes of the urea cycle lead to?
hyperammonaemia and accumulation/excretion of urea cycle intermediates
What are the symptoms of defects in the urea cycle?
vomiting, lethargy, irritability, seizures, mental retardation
What is the management for defects in the urea cycle?
low protein diet and replace amino acids in diet with keto acids
What are some of the toxic effects of ammonia?
interference with amino acid transport and protein synthesis, increase in pH, alteration of blood brain barrier, interference with TCA cycle
What are the 2 ways that ammonia can be transported safely?
combine with glutamate for transportation as glutamine or combine with pyruvate for transportation as alanine
What does the heel prick test for?
sickle cell disease, cystic fibrosis, congenital hypothyroidism and inborn errors of metabolism
What is phenylketonuria?
The most common inborn error of amino acid metabolism due to a deficiency in phenylalanine hydroxylase. Phenylalanine accumulates in tissues to phenylketones will be present in the urine. This prevents the formation of tyrosine by the body.
Which pattern of inheritance does PKU follow?
Autosomal recessive
What is the treatment for PKU?
low phenylalanine diet, avoid artificial sweeteners, avoid high protein foods
What is the major problem with PKU?
No tyrosine can be made and therefore we cannot make many other molecules.
eg. dopamine, adrenaline, thyroxine, melanin
What are the symptoms of PKU?
developmental delay, intellectual disability, microcephaly (small head), seizures, hypopigmentation
What causes homocystinurias?
There is a problem breaking down methione and therefore an excess of homocysteine. Most commonly due to a defect in cystathionine beta-synthase.
Which pattern of inheritance do homocystinurias follow?
autosomal recessive
What is the treatment for homocystinurias?
low methione diet, avoid high protein foods, avoid nuts, take vitamin supplements
What is elevated homocysteine shown to be associated with?
Increased risk of cardiovascular disease
