Protein Metabolism and Nitrogen Balance Flashcards
How are proteins absorbed
- absorbed in ileum as amino acids via secondary active transport
- digestion is slow ( hours )
Describe protein concentration in tissues and what happens to excess
- high turnover between tissues = rapid distribution
- will be expelled in urine if there is too much and proximal tube can’t reabsorb
Describe the metabolism of proteins
- broken into amino acids which are used for energy
- Amino acids undergo deamination which breaks it into glucose, fatty acids and ketone and Ammonia
- ammonia is expelled in urea
How are amino acids stored? what happens when protein is needed?
- free amino acids can’t be stored so they combine to form peptides and intracellular proteins
- when protein is needed intracellular proteins are degraded into amino acids and the transported in blood
Where are proteins stored
- liver stores most proteins along with kidneys and intestinal mucosa
- can’t be stored by cells unless AA convert to fat/glycogen
What influences the storage of amino acids
- hormone and insulin increases protein synthesis
- glucocorticoid mobilize amino acids for energy
What are the 4 plasma proteins and their function
- Albumin : generates osmotic pressure
- Globulins : innate and acquired immunity
- Transferrin : carry ferrous ions
- Fibrinogen: mediates clot formation and repairs leaks in Circulation
What produces plasma protein and what can affect the rate of production
- plasma is formed by the liver
- in stress conditions production increases
- in liver disease it decreases and thus causes oedema
List the 4 stages of protein metabolism in liver
1- Transamination
2- Deamination
3- Oxidation
4- Excretion
Describe Transamination & the main substrate used
- amino group transferred from amino acid to alpha keto acid by aminotransferase
- glutamine amino is usually used
What is the effect of aminotransferase on protein synthesis
aminotransferase used vitamin B6 which decreases protein synthesis
Describe Deamination
- amino group is removed from amino acids
- amino acid is converted to ammonia which is excreted in urea
Describe role of alpha ketoglutarate
- amino acid and alpha ketoglutarate through aminotransferase will make glutamate and alpha keto acid.
- glutamate will make ammonia
- alpha ketoglutarate can also enter TCA cycle (gluconeogenesis )
Explain Gluconeogenesis and amino acids
- alpha ketoglutarate will enter TCA cycle which contains amino acids
- amino acids can also generate pyruvate
Explain Ketogenesis and amino acids
- amino acids can create Acetyl CoA
- synthesise ketones and lipids
What are the 5 classes of amino acids
1- Essential 2- Non-essential 3- Glucogenic 4- Ketogenic 5- Glucogenic and Ketogenic
How is Urea formed
- Ammonia released from deamination is ionized with carbon dioxide to create ammonium ( NH4)
- one amino from ammonium makes citrulline that combines with amino from aspartate to make arginine that with water becomes urea
What does Urea contain
Ornithine Carbamoyl phosphate ( reactor ) Citrulline Aspartate ( reactor ) Arginiosuccinate fumarate arginine = urea
What is the purpose of Urea
prevents toxic build up of ammonium
how is Protein used as a source of energy and when
- used for gluconeogenesis
- only used if all carb and fat stores are used
What happens with liver phosphorylase deficiency
- will not be able to mobilize glycogen from liver and thus gluconeogenesis and ketogenesis will be used for fuel
Growth hormone effect protein metabolism
- promotes synthesis of cellular protein
- increase amino acid membrane transport
- increase RNA transcription
Insulin effect on protein metabolism
- promotes cellular uptake of AA
- inhibits protein catabolism
- increase RNA transcription
- decrease gluconeogenesis
What hormones are needed for protein synthesis
- growth hormone and insulin
- needed TOGETHER
Testosterone and Oestrogen effect on protein metabolism
- T: transient muscle growth
- O: minor muscle growth relative to testosterone
Thyroxine effect on protein metabolism
- increases cell metabolism which activates catabolic protein pathways
- will increase protein synthesis if high carbs and fats and degradation if low
Glucocorticoids effect on protein metabolism
- increase protein break down and circulating AA and plasma proteins
Explain Citrullinemia
deficiency in arginosuccinate synthase results in accumulation of ammonia in blood
Explain Tyrosinemia
defective liver tyrosine aminotransferase will result in liver disease, osteoarthritis and mental retardation
Explain Phenylketonouria
mutation in PAH gene result in lack of phenylalanine hydroxyls which damages CNS
What is nitrogen balance and its purpose
- nitrogen is fundamental part of AA
- balance is determined by amount consumed and excreted
- nitrogen will indicate protein metabolism , if intake is greater than loss then no demand of stored protein breakdown
Effects of negative nitrogen balance
- Cachexia : loss of body mass
- hyper metabolic state : constant protein break down which can lead to sepsis
