Chapter 19 : amino acid synthesis and metabolism
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Transcript of Chapter 19 : amino acid synthesis and metabolism
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Amino acids synthesis and metabolism
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Ways to get energy
● Energy which occurs in the form of ATP can be gotten from acetyl CoA through the TCA cycle.
● Sources of acetyl CoA : – Beta oxidation of fatty acids
– Pyruvate by the action of PDC
– Amino acids metabolism
PS: PDC is the pyruvate dehydrogenase complex
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Steps to exploit amino acids
1)Deamination
2)Oxidative decarboxylation ( production of CO2 and NADH )
3)Dehydrogenation (that resembles betta oxidation to some point).
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methods of deamination
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Transamination
● Definition : transfer of amine from amino acid to be utilized to a ketoacid ( alpha ketoglutarate or oxaloacetate) by the enzyme aminotransferase (transaminase) which Needs pyridoxine (B6) as a cofactor
● All amino acids can undergo transamination except lysine ● Safest way because amine NH3 is a non-soluble toxic molecule
● A.A. + alpha ketoacid →alpha ketoacid + aspartate/ gulatamate
PS: if OAA is used then the product is aspartate however if alpha ketoglutarate is used then the product is glutamate
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Oxidative deamination
● The amine is extracted as a free NH3 by the enzyme oxidase
● This method includes the reduction of FMN to FMNH2
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Non oxidative dehydration
● By the enzyme dehyratase ● It involves the removal of free NH3 from the
amino acid● Just for the amino acids : serine and threonine
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Disorders in Amino acid metabolism
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PKU
● Deficiency in phenylalanine hydroxylase which leads to deficiency in the degradation of phenylalanine and synthesis of tyrosine
● The phenylalanine is transformed to phenylactate and phenylpyruvate
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Alkaptonuria
● Deficiancy in the enzyme that oxidize the homogenistic acid intermediate in the catabolism of tyrosine and phenylalanine so the oxidation of this intermediate in the urine leads to its black color
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Maple syrup urine disease (MSUD)
● Involves a mutation in the decarboxylase enzyme that convert the alpha keto acid ( of the LIV amino acids ) to acetyl COA
● Leads to accumulation of ketoacids and then to ketoaciduria
LIV : leucine isoleucine and valine
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Syntehsis of amino acids
● Synthesis of the carbon skeleton first ( ketoacid) then the addition of ammonia
● Some backbones can be synthesized => non essential whereas others can't be synthesized and should be supplied by the diet => essential
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Essential amino acids
● TV TILL PM HA ?● T: threonine and tryptophan ● I: isoleucine ● L: leucine lysine ● P: phenylalanine ● M: methionine ● H : histidine ● A: alanine
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Nonessential that come from essential aa
● The sulfur of non essential cysteine comes from methionine
● Tyrosine is synthesized from phenylalanine
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Role of amino acids :
● Building block of protein ● Energy ● Excitatory neurotransmitters : aspartate and
glutamate ● Inhibitory neurotransmitters ● Precursors of neurotransmitters● Hormones
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Glucogenic / ketogenic / both
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Glucogenic aminoacids Amino acids
Keto acids + glutamate/ aspartate
OAA
fumarate/proprionyl CoA/ketoglutarate/ pyruvate
glucose
PEP
AAA CC GGG HM PSV
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● Asparginine● Arginine● Alanine
● Cysteine ● Cystine● Glycine
● Glutamic acid● Glutamine● Histidine
● Methionine● Proline● Serine● Valine
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Ketogenic
Oxidative decarboxylation
Acetyl coA/ aetoacetate
dehyrogenation
Amino acid
PS : acetyl CoA and ketone bodies join the TCA cycle without being carbon donors for oxaloacetate ( disappear AS 2 co2)
LEUCINE LYSINE
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both
● Gives both glucogenic and ketogenic precursors
● Phenylalanine● isoleucine ● Tyrosine● Tryptophan● threonine
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Regulation of Urea cycle
● Regulation of synthesis of N acetyl glutamate the cofactor of CPS1 by arginine concentration ( directly proportional )
● Protein diet stimualte the enzymnes of urea cycle● Acidosis leads to removal of NH3 as NH4+ instead as
urea so the cycle is inhibited ● In case of fasting amino acids are degraded and more
amine are produced so the cycle is stimulated
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Regulation of amine in blood
● Glutamine is a buffer for amine● The respective transformation between different
forms containing different number of amine regulate amine concentration in blood either release or absorb
glutaminase Glutamate DH
Glutamine synthetase transaminase
Glutamine(2 NH3)
Ketoglutarate (no NH3)
Glutamate (1 NH3)
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Nitrogen balance
● Neutral (excreted = taken) ● Positive(excreted < taken) in growing or
regenerating cells so more protein is synthesized ● negative(excreted > taken) in case of protein
malnutrition or fasting so that some un-necessary aa are degraded to be utilized later on in producing other important aa or energy so more NH3 is produced