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 Synthesis and degradation of Amino acids  Synthesis and degradation of Amino acids

Synthesis and degradation of Amino acids - PowerPoint Presentation

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Synthesis and degradation of Amino acids - PPT Presentation

1 Overview The catabolism of the amino acids involves Removal of αamino groups Breakdown of the resulting carbon skeletons The resulting compounds will be used to form seven intermediate products ID: 775056

amino acids pyruvate synthesis amino acids pyruvate synthesis ketoglutarate carbon alanine coa acid skeleton glutamate phenylalanine metabolism homocysteine threonine

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Slide1

Synthesis and degradation of Amino acids

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Slide2

Overview The catabolism of the amino acids involves:Removal of α-amino groups. Breakdown of the resulting carbon skeletons.The resulting compounds will be used to form seven intermediate products: oxaloacetate, α-ketoglutarate, pyruvate, fumarate, succinyl coenzyme A (CoA), acetyl CoA, and acetoacetate. These products directly enter the pathways of intermediary metabolism, resulting either in the synthesis of glucose or lipid or in the production of energy through their oxidation to CO2 and water by the Krebs cycle.

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Slide3

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Slide4

Essential amino acids in humans

Arginine* Histidine* Isoleucine Leucine Valine

Lysine Methionine Threonine Phenylalanine Tryptophan

*Required to some degree in young growing period and/or sometimes during illness.

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Slide5

Non-essential amino acids in humans

Alanine Asparagine Aspartate Glutamate Glutamine

Glycine Proline Serine Cysteine (from Met*) Tyrosine (from Phe*)

* Essential amino acids

Can be formed from a-keto acids by transamination and subsequent reactions.

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Slide6

Metabolic relationship of amino acids

BODY PROTEINS

Proteosynthesis

Degradation

AMINO ACIDS

DIETARY

PROTEINS

GLYCOLYSIS

KREBS CYCLE

Digestion

Transamination

NONPROTEIN

DERIVATIVES

Porphyrins

Purines

Pyrimidines

Neurotransmitters

Hormones

Komplex lipidsAminosugars

UREA

NH

3

Conversion

(Carbon skeleton)

250 – 300

g/day

ACETYL CoA

GLUCOSE

CO

2

KETONBODIES

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Biosynthesis of amino acids :transamination reactionsAll amino acids except threonine, lysine, and proline can be transaminated

amino acid1 +a-keto acid2 amino acid2 +a-keto acid1

Glutamate

+

a

-

Ketoglutarate

+

Pyridoxal phosphate (PLP)-

d

ependent

a

minotransferase

Keto-acid

Amino acid

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Slide8

Clinicaly

important transaminases

ALT

Alanine-a-ketoglutarate transferase ALT(also called glutamate-pyruvate transaminase – GPT)Aspartate-a-ketoglutarate transferase AST(also called glutamate-oxalacetate transferase – GOT)Important in the diagnosis of heart and liver damage caused by heart attack, drug toxicity, or infection.

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Slide9

Glucose-alanine cycle

Ala

is the carrier of ammonia and of the carbon skeleton of pyruvate from muscle to liver.The ammonia is excreted and the pyruvate is used to produce glucose, which is returned to the muscle.

Alanine plays a special role in transporting amino groups to liver.

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Glucogenic Amino Acids

formed: a-ketoglutarate, pyruvate, oxaloacetate, fumarate, or succinyl-CoA

Aspartate Asparagine ArginineProline

Methionine Valine Glutamine Glutamate Threonine

Alanine Serine Cysteine Glycine Histidine

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Slide11

Ketogenic Amino Acids

formed acetyl CoA or acetoacetate

LysineLeucine

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Slide12

Both glucogenic and ketogenic amino acids

formed: a-ketoglutarate, pyruvate, oxaloacetate, fumarate, or succinyl-CoA in addition to acetyl CoA or acetoacetate

IsoleucineTryptophanPhenylalanineTyrosine

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Alanine

Serine

Cysteine

Threonine

The C3 family: alanine, serine, cysteine and threonine are converted to pyruvate

Pyruvate

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The C4 family: aspartate and asparagine are converted into oxalacetate

Aspartic acid

Asparagine

Oxalacetate

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The C5 family: several amino acids are converted into a-ketoglutarate through glutamate

Glutamine

Proline

Histidine

Arginine

a-

ketoglutarate

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Slide17

Interconversion of amino acids and intermediates of carbohydrate metabolism and Krebs cycle

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Slide18

Synthesis of Ala, Val, and Lue

—Ala, Val, and Lue are derived from pyruvate (EMP)

carbon skeleton

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Slide19

Synthesis of Ser, Gly and Cys

—Ser, Gly, and Cys are derived from 3-phosphoglycerate

(EMP)

carbon skeleton

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Slide20

Synthesis of Glu, Gln, Pro and Arg

—α-Ketoglutarate (TCA) gives rise to Glu, Gln, Pro, and Arg synthesis

carbon skeleton

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Slide21

—Oxaloacetate(TCA) gives rise to Asp, Asn, Met, Lys, Thr synthesis

carbon skeleton

Synthesis of

Asp, Asn, Met, Lys,Thr and Arg

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Slide22

Synthesis of His

carbon skeleton

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Slide23

Diseases related to the amino acid metabolism

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There is a not a proven cause and effect relationship of elevated homocysteine with cardiovascular disease.Elevated plasma homocysteine levels are an independent cardiovascular risk factor that correlates with the severity of coronary artery disease.Dietary supplementation with folate, vitamin B12 and vitamin B6 the three vitamins involved in the metabolism of homocysteine to a reduction in circulating levels of homocysteine.

Role of homocysteine in vascular disease

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Deficiency of phenylalanine hydroxylase (common) or deficiencies in the enzymes that synthesize or reduce the coenzyme BH4.Elevated levels of phenylalanine, phenyl- lactate, phenylpyruvate in plasma and urine  characteristic mousey odor of urine.

CNS symptoms: Mental retardation, failure to walk or talk, seizures, hyperactivity, tremor

Hypopigmentation:

deficiency of

pigmentation (fair hair, light skin color, and blue eyes) < hydroxylation of tyrosine by tyrosinase, which is the first step in the formation of the pigment melanin

Phenyl ketouria

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Neonatal diagnosis of PKU : laboratory

testing for elevated blood levels of

phenylalanine is mandatoryHowever, fetus at birth  normal level of phenyl-alanine (mother)  tests performed at birth may show false negative results  exposure of new born to protein diet 24 h after birth  better results.Treatment of PKU: feeding synthetic amino acid preparations low in phenylalanine, supplemented with some natural foodsMaternal PKU : When mother suffering from PKU + high level on phenylanaline  microcephaly, mental retardation, and congenital heart abnormalities in the fetusDietary control of blood phenylalanine prior to conception, and must be maintained throughout the pregnancy

Phenyl ketouria

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Slide27

A rare metabolic disease involving a deficiency in

 accumulation

acid oxidase acid

(degenerative pathway of

homogentisic homogentisic tyrosine)Characteristic

symptoms:

homogentisic aciduria

which is oxidized to a dark pigment on standinglarge joint arthritis and black pigmentation of cartilage and collagenous tissuePatients are without symptoms till 40Diets low in protein may help

Alkaptonuria

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Slide28

AlbinismA group of conditions with a defect in tyrosine metabolism  a deficiency in the production of melanin  partial or full absence of pigment from the skin, hair, and eyes.Oculo-cutaneous albinism: due to a deficiency of tyrosinase activity, causing a total absence of pigment from the hair, eyes, and skin The most severe form of the condition. Affected people may appear to have white hair, skin, and photophobia (sunlight is painful to their eyes), they sunburn easily, and do not tan.

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