Liver Flashcards
How do skeletal muscle cells convert and transport ammonia to the liver
- glutamate + pyruvate = alanine + alpha ketoglutarate
- enzyme = alanine transaminase (ALT)
- alanine moves in the blood and transports ammonia to the blood
ammonia + alpha ketoglutarate = glutamate
-enzyme = glutamate dehydrogenase
How is ammonia released in the liver from different molecules to enter the urea cycle
- glutamate = alpha ketoglutamate + ammonia
- enzyme = glutamate dehydrogenase
- glutamate + oxaloacetate = alpha ketoglutarate + aspartate
- enzyme = aspartate transminase (AST)
- alanine + alpha ketoglutarate = glutamate + pyruvate
- enzyme = alanine transaminase (ALT)
Which amino acid is the only one that can directly enter the urea cycle
-aspartate
What organic groups are the urea made of
- 2 nitrogen groups
- 1 carboxyl group
What is the first step of the urea cycle
- ammonia + CO2 + 2ATP (bicarbonate) = carbamoyl phosphate
- enzyme = carbamoyl phosphate synthetase 1 (CPS1)
- this is the rate limiting step because of the n-acetylglutamate
Which molecule allosterically activates carbamoyl phosphate synthetase 1 (CPS1)
N-acetlyglutamate
-so increases the rate of urea synthesis
What molecules form n-acetylglutamate
- glutamate + acetly-CoA = N-acetylglutamate
- enzyme = n-acetylglutamate synthestase
What is the 2nd step of the urea cycle
- Ornithine + Carbamoyl phosphate = Citrulline + free phosphates
- enzyme = orthinine transcarbamoylase
What is the 3rd step of the urea cycle
- citrulline + aspartate + ATP = arginino-succinate
- enzyme = argininosuccinate synthetase
What is the 4th step of the urea cycle
- arginino-succinate = fumarate + arginine
- enzyme = arginino-succinate lyase
What is the fumerate from the 4th step of the urea cycle used for
- fumerate = malate
- malate =oxaloacetate (enzyme - malate dehydrogenase)
Why is oxaloacetate and aspartate transminase (AST) enzyme important in the urea cycle
-they regenerate aspartate to enter the urea cycle
What molecule is directly broken down to make urea and by which enzyme
- arginine = urea + ornithine
- enzyme = arginase
What makes up a nucleotide
- 5 carbon sugar (either deoxyribose or ribose)
- phosphate group
- nitrogenous base
Give the 3 pyrimidine bases
- cytosine
- thyamine
- uracil
Give 2 purine bases
- guanine
- adenosine
What is a nucleoside
- nitrogenous base
- 5 carbon sugar
Give the names of some DNA nucleosides and the RNA counterparts
- deoxyadenosine (DNA) and adenosine (RNA)
- deoxyguanosine and guanosine
- deoxycytidine and cytidine
- deoxythymide and uridine
What are the 2 ways of making nucleotides (nucleotide synthesis)
- de novo synthesis
- salvage pathway (from diet too)
How does de novo synthesis occur
Starts with
- ribose 5-phosphate + ATP = AMP + phosphoribosyl pyrophosphate (PRPP)
- enzyme = ribose phosphate pyrophoshokinase
Which enzyme converts RNA nucleotides (in diphosphate form) to DNA nucleotides
-ribonucleotide diphosphate reductase
What is different about how purines and pyrimidines can be broken down
- pyrimidines can be broken down completely into CO2 + NH3 (ammonia) which can be exhaled by the lungs or removed by the kidneys
- purines are converted into uric acid which is then excreted into urine
How does gout occur
- build up of uric acid which enters joints and tendon
- the uric acid becomes monosodium urate which crystallises
- the body forms proteins around these crystals and the complex is called tophi
- and tophi causes an inflammatory reaction called gout which usually occurs in the big toes
How does salvage pathway produce nucleotide
- hypoxanthine and guanine from purine degradation are converted back to GMP (guanine monophosphate) and IMP (iosine monophosphate) which can be converted to AMP (adenosine monophosphate)
- through enzyme hypoxanthine guanine phosphoribosyl transferase (HGPRT) which returns the ribose and phosphjate group back to hypoxanthine and guanine
