Week 3 Amino Acid Metabolism Nitrogen Balance Module Flashcards
of the 20 AA how many can be generated by the bodY
11
protein accounts for what % of nitrogen in body?
95%
how are lipids stored int he body?
adipose tissue
how is glucose stored in the body?
glycogen (liver, muscle)
how is protein stored in the body?
its not!
what are the three states of nitrogen balance?
negative, positive, equilibrium
what is a negative nitrogen balance?
inadequate nitrogen intake or hyper-catabolic state
what is positive nitrogen balance?
a person is accumulating protein in the body over what is needed to maintain lean body mass (ideal for growing children)
what is the free amino acid pool?
ALL free amino acids of the body. those present in all tissues including blood.
what are the pathways that deplete the free amino acid pool (3)?
protein translation, nitrogenous compound biosynthesis, amino acid catabolism
what are the pathways that maintain the amino acid pool?
degradation of body proteins, dietary amino acids, biosynthesis of non-essential AA
what is the largest compartment of amino acids?
body proteins
what is protein turn over?
refers to the total flux (in and out) of proteins through protein synthesis and protein degradation pathways
how does lean tissue deposition occur?
protein synthesis>protein degradation
how does lean tissue wasting occur?
protein degradation>protein synthesis
which amino acids can be converted to purines and pyrimidines? 3
Gly, Asp, Gln
Along with Pur and Pyr, Gly is also a precursor for what to molecules?
heme and creatine
what neurotransmitters origanate from the free AA pool?
serotonin (Trp), GABA (Gln), histamine (His), EP, NE (Tyr)
NO is made from what AA
Arg
when the body degrades amino acids, what occurs to the N?
excreted in urine
what is the significance of N being excreted in the urine?
gives us a window to body protein homeostasis
nitrogen equilibrium exists when
nitrogen intake= excretion
when we have a positive nitrogen balance?…what state is the body in
intake>excretion and the protein compartment grows. anabolic state
when is positive nitrogen balance required?
in normal growth, (supports gains in lean body mass)
what is a negative nitrogen balance? what state?
excretion>intake. catabolic state
when the body is in a negative nitrogen balance how is free amino acid pool maintained?
proteins are degraded
which compartment (amino acid pool or body protein) is maintained within a narrow compartment
amino acid pool! the pathways that add to it and take from it are narrowly regulated
nitrogen balance is measured by….
nitrogen ingested-nitrogen excreted
what is a non-nutritional cause of negative nitrogen balance
cachexia
what is cachexia? cause? seen in? treatment?
a hyper-catabolic state. results in profound weight loss. seen in cancer, chronic renal disease, severe burns. Treat: stimulate anabolism (steroids)
anabolism:
building
catbolism
breaking down
what do anabolic steroids do to nitrogen balance?
lead to a large increase in nitrogen balance where less nitrogen is being excreted. build protein (and muscle)
most of the body protein is in…
skeletal muscle (40%)
if a decrease in dietary protein does not explain cachexia, what does?
the inflammatory response. cytokines catabolize skeletal muscle causing an influx in the AA pool and a correlated increase in AA breakdown
why are some AA ‘essential’?
out body doesnt have the machinery to produce them. Probably an evolutionary thing that resulted in us conserving energy by eliminating the need to synthesize some of the more metabolically complex AA
compared to essential AA, the number of proteins needed to make non-essential AA is….
far less. Essential AA would require an average of 6.6 additional enzymes per AA
why are Tyr and Cys conditionally non-essential?
they can be synthesized from the essential Phe and Met
the N equilibrium is determined mainly by…
the most limiting AA (essential), the N equilibrium point will differ for protein sources of different quality
what is an incomplete protien?
protein that does not provide all the essential AA
what does a nitrogen balance curve look like for incomplete proteins?
smaller slope and larger x-intercept
where is nitrogen equilibrium on a nitrogen balance curve?
the x-intercept
all non-essential AA except Tyr and Cys can be synthesize by…
transamination from Glutamate
Phe+Phe hydroxylase–>
Tyr
a deficiency in Phenylalanine hydroxylase results in…
phenylketonuria (PKU)
what is the cofactor of Phe hydroxylase?
tetrahydrobiopterin
co factor
a molecule essential of enzyme function
Phe hydroxylase deficiency can be caused by which two things?
mutation in gene encoding Phe hydroxylase or an inability to regenerate tetrahydrobiopterin
why is Phe hydroxylase deficiency a problem? (2)
its product (Tyr) becomes an essential AA along with its downstream metabolites. Also, an increase in the reactant (Phe) leads to the accumulation of neurotoxic metabolites of phenyllactate and phenylacetate
what is the therapy for PKU?
suppmlment Tyr and avoid Phe (things that contain aspartame such as artificial sweeteners)
how is the (conditionally) non-essential AA Cys produced?
in two steps from the non-essential AA Ser with the help of the essential AA Met
How does Met contribute to Cys synthesis
donates its sulfur, through its metabolite homocysteine (these are the only two sulfur containing AA)
what is homocystinuria? cause?
rare recessive disorder caused by a mutation in the gene coding for cystathionine synthase (CBS)
what is the role of CBS?
role in producing Cys from Met and Ser
what accumulates in people with homocystinuria? why is this bad?
Met, homocysteine. homocysteine disrupts collagen cross-linking and leads to premature atherosclerosis, strokes, heart attacks, and mental retardation
how is homocystinuria treated?
diet: limit Met and supplement Cys
what is cystathioninuria?
a disorder in which cystathionine (metabolite of homocystein) accumulates. relatively benign because this intermediate doesnt feed into many pathways
how is Asn (non-essential) asparagine produced? enzyme
in a single step from aspartate (Asp) with the enzyme asparagine synthetase (requires ATP)
what is the cause of acute lympahtic leukemia?
Asparagine snythetase deficiency in WBCs. Asn can’t be produced and becomes essential AA
what is the treatment for acute lymphatic leukemia?
administration of L-asparaginase (enzyme in prokaryotes that converts Asn TO Asp) that depletes Asn and kills cancerous leukocytes
how is glutamine (Gln) produced?
in a single step from Glu and ammonia by the enzyme glutamine synthetase (requires ATP)
what is the most abundant AA
Gln
What can be said about Gln transfer among organs
it is the FASTEST making Gln a major vehicle in N transfer among tissues
Cachexia also depletes what AA (along with protein)?
Gln, therefore supplementing Gln is used to treat Cachexia
what are important conditions that require a positive nitrogen balance?
pregnancy and childhood growth
what are two causes of a negative nitrogen balance?
malnutrition, cachexia
