BIOC L6 - nitrogen metabolism

Why must we metabolise nitrogen?

nitrogen particularly in the form of ammonia in the blood is toxic

What is nitrogen important in?

signaling molecules and hormones

How are amino acids absorbed into the blood?

active transport via Na+ pump

What is the relationship between alanine and pyruvate?

alanine is a non-essential amino acid made from pyurvate which is the ketoacid of alanine

What happens if the diet is deficient in phenylalanine?

cannot make tyrosine which is a non-essential amino acid important for making other downstream molecules

Why is arginine listed as a non-essential and essential amino acid?

in adults arginine is non essential but in growing individuals it is essential from the diet

What is tyrosine a precursor for?

dopamine, adrenaline, serotonin, melatonin, thyroid hormones

What are histidines needed for?

to make histimines which are part of the immune response, digestion and brain function

What is arginine needed for?

can form nitric oxide for cardiovascular protection and for neurotransmitters

What is creatinine?

derived in skeletal muscles

What are urine creatinine levels proportional to?

muscle mass

What are blood creatinine levels a measure of?

kidney function

Who is likely to have a slightly higher creatinine output?

someone who is actively building muscle

What are fates of amino acid carbon skeletons?

CO2 + H2O, glucose, acetyl coA, and ketone bodies

What is the relationship between glutamate and glutamine?

both are connected to a-ketoglutarate and are important in urea cycle

What are N containing products excreted in urine?

urea, ammonia, uric acid, and creatinine

What does urea excretion indicate?

dietary protein, the more protein we eat, the larger amount of urea we excrete

Where does uric acid come from?

purine (A and G) catabolism

What could elevated blood uric acid levels show?

gout - issues with joints

What is nitrogen balance?

measure of N input vs N output which is dependent on dietary N intake and physiological state

What percentage of protein consumed is purely nitrogen?

16%

How else can nitrogen be lost excluding urine?

faeces, skin and hair loss, and bodily fluids (approximately 2.5g)

What is a positive nitrogen balance?

holding onto more nitrogen than excreting

What is a negative nitrogen balance?

excreting more nitrogen than consuming

What could be the reasons that someone has a positive nitrogen balance?

childhood and adolescent growth, pregancy, body building - all need nitrogen for growing muscle

What could be the reasons that someone has a negative nitrogen balance?

injury, surgery or infection, starvation - repair and starvation requires the breakdown of muscle protein for healing or energy, loss of appetite or limited access to food means these can't be replenished