Metabolisme Protein SaryonoBagian Biokimia

Protein1. Large molecules, 103 to 108amu2. Polymers of amino acids in specific sequences3. Sequence determines function4. Homo sapiens, 20 different amino acids make up all proteins

Asam amino dan proteinAsam amino terdiri dari gugus karboksilat dan gugus aminoProtein tdr dari beberapa asam amino yang terikat dengan ikatan peptide.Ikatan peptida adalah ikatan yang menghubungkan gugus amin dari suatu asam amino dengan gugus karboksilat dari senyawa asam amino yang lain

Asam amino sebagai ion dipolarKarena mengandung gugus karboksilat dan gugus amino, maka dapat bersifat zwitter ion (bermuatan +/-)Walaupun netral, tetapi ion dipolar masih merupakan senyawa ionSifat fisik: titik didih tinggi, dapat larut dalam air, tetapi tidak larut dalam pelarut organikIon dipolar bersifat amfoter, dapat bereaksi dengan asam/basa

Berdasarkan rantai sampingAsam amino netral:alanin, glisin, isoleusin, leusin, metionin, fenilalanin, prolin, triptofan, valinAsam amino polar+nonpolarAsam amino basa: arginin, lisin dan histidinAsam amino asam: asam aspartat dan asam glutamat

Asam aminoSemua asam amino kecuali glisin, pada atom C-2 terikat 4 gugus yang berbeda: gugus karboksilat, gugus amino, atom H dan rantai samping RAA alifatik: Gly, Ala, Val, Leu, IleAA mengandung S: Cys, MetAA mengandung gugus OH: Ser, Thr, TryAA mengandung gugus asam : Asp, Asn, Glu, GlnAA mengandung cincin aromatik : His, Phe, Tyr, TrpAA mengandung gugus basa: Arg, Lys, HisAA imino: Pro

Protein Types1. Structural- provide structurea. Collagen- tendons & cartilageb. Keratin- hair, skin, wool, & nailsc. Spongin- sponges, Porifera2. Contractile- movement, muscles & filamentsa. Myosin- contractile ms filamentb. Actin- anchor ms filament

Protein Types3. Transport- carry substances in bodya. Hemoglobin & hemocyan- transport O2b. Lipoproteins- transport lipids4. Storage- store nutrientsa. Casein- stores protein in milkb. Albumin- stores protein in eggs & bloodc. Ferritin-stores iron in spleen & liver

Protein Types5. Hormone- regulate metabolism & nervous systema. Insulin- regulates blood glucose levelsb. Somatropin- growth hormone, regulates growth phases

Protein Types6. Enzyme- catalyse biochem rxna. Sucrase- hydrolysis of sucroseb. Trypsin- hydrolysis of proteins7. Protection- defense of organisma. Immunoglobulins- stimulate immune responseb. Venoms- poisons to kill, stun, or discourage attackers

Enzymes1. Protein catalysts that lower activation energy & # rxn rate of cellular chemical reactions required for metabolism2. Pepsin, trypsine, sucrase, lipases, carbonic anhydrase

Amino Acids1. H atom, amino group, carboxyl group, & functional group attached to central carbon, aC2. Different functional groups determine characteristics of individual amino acids3. Nonpolar aa, polar aa, acidic aa, basic aa

Non-Essential Amino Acids in Humans Not required in diet Can be formed from a-keto acids by transamination and subsequent reactions Alanine Asparagine Aspartate Glutamate Glutamine Glycine Proline Serine Cysteine (from Met*) Tyrosine (from Phe*)* Essential amino acids

Essential Amino Acids in Humans Required in diet Humans incapable of forming requisite carbon skeleton Arginine* Histidine* Isoleucine Leucine Valine Lysine Methionine Threonine Phenylalanine Tryptophan* Essential in children, not in adults

Amino Acid Structure

amino carboxyl group group

functional group

Nonpolar Amino Acids1. Hydrophobic aromatic group or hydrocarbon chain2. Glycine, alanine, valine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan

Polar Amino Acids1. Hydrophilic functional groups2. Serine, threonine, asparagine, cysteine, tyrosine, glutamine

Acidic Amino Acids1. Carboxylic acid on functional group2. Aspartic acid, glutamic acid

Basic Amino Acids1. Amine group on functional group2. Lysine, arginine, histidine

Essential Amino Acids1. Ten aa are essential, must be in diet2. Essential- arg, his, ile, leu, lys, met, phe, thr, trp, val3. Ten aa can be synthesized from essentials4. Nonessential- ala, asn, asp, cys, gln, glu, gly, pro, ser, tyr

Dipolar IonDipolar ion- carboxyl group donates H+ and amino grp accepts H+

alanine, dipolar ion

Amino Acid Ionization1. Most aa exist as dipolar ions, net charge = 02. In acid soln, carboxyl grp accepts H+ & aa has positive charge3. In basic soln, amino grp donates H+ & aa has negative charge

Peptide bond1. Amide bond between carboxyl grp of one aa & amino grp of another2. Small peptides named starting at amino group using -yl or 3 letter abbreviations

Tripeptidealanylglycylserine or ala-gly-ser, a tripeptide

AspartameL-aspartic acid & methylesterphenylalanine

Polypeptide1. Long chains of amino acids2. Protein- >50 amino acids3. Primary, secondary, tertiary, & quaternary structure

Struktur proteinStruktur primer;urutan/order AA dalam rantai proteinStruktur sekunder;Alfa heliks;tulang punggung terpilin membentuk coil/ulirBeta pleated sheet; lembaran terlipat betaParalelAntiparalel Ikatan hidrogen, interaksi hidrofob, interaksi elektrostatik, interaksi van der waalsStruktur tersier; lipatan/gulungan yang kompleksIkatan disulfida memberikan stabilitas tambahanStruktur kwaterner; persekutuan unit protein

Primary Structure, 1o1. Sequence of amino acids in protein, 1o sequence determines function2. Thyroxine Releasing Hormone- glu-his-pro sequence3. Insulin- two chains, 21 aa in a chain & 30 aa in b chain

Secondary Structure1. Alpha helix2. Beta plate sheet3. Triple helix

Alpha Helix1. Hydrogen bonds between amino groups & carbonyl groups twist amino acid chain into a helix or spiral2. Functional groups are outside

Beta Sheet1. Hydrogen bonds between amino groups & carbonyl groups fold parallel amino acid chains into pleated sheet2. Functional groups are on opposite sides of sheet

Triple Helix1. Three amino acid chains woven into a braid2. Structure of collagen, found in connective tissue, skin, tendons, ligaments

Tertiary1. Three dimensional shape of protein2. Attractions & repulsions from side groups fold protein into specific shape3. Globular proteins- compact & roughly spherical, polar4. Fibrous proteins- long & thin fibers, structural

Quaternary1. Two or more polypeptide units held together by side group interaction2. Hemoglobin- globular, two a chains & two b chains

Protein Denaturation1. Bonds that stabilize the 2o, 3o, or 4o structure weakened or broken2. Heat, acids, bases, certain organic compounds, heavy metal ions, & agitation

Amino Acid BiosynthesisPlants and microorganisms can make all 20 amino acids and all other organisms need N metabolites In these organisms, glutamate is the source of N, via transamination (aminotransferase) reactions Mammals can make only 10 of the 20 amino acids The others are classed as "essential" amino acids and must be obtained in the diet All amino acids are grouped into families according to the intermediates that they are made from

Biosintesis asam aminoVertebra tidak dapat melakukan biosintesis asam amino essensialHanya non essensial yang dapat disintesis dari senyawa antara amfibolik lewat lintasan metabolikSenyawa antara : siklus asam sitrat, alfa ketoglutarat (Glu, Gln, Pro, Hyp), oksaloasetat (Asp, Asn), serta senyawa bersifat glikolitik, 3-fosfogliserat (Ser, Gly)Ketiga AA lainnya (Cys, Tyr, Hyl) dibentuk dari asam amino essensial

Glutamate-dependent transamination - primary mechanism for amino acid synthesis

Asam amino esensialDiabsorpsi melalui:Transport tergantung Na+Difusi terfasilitasiTransport terikat pada -glutamyl cycle

Transport tergantung Na+Na+ di dalam sel intestinal rendah o/k dipompa keluar ke sisi serosa oleh pompa Na,K,ATPaseNa+ dan asam amino dipompa masuk ke sel dari lumen intestinalAA dibawa dengan transporter terfasilitasi di dalam membran serosa ke darah

-glutamyl cycleDi dalam ginjal dan intestinalAA ekstrasel berreaksi dengan glutation---menjadi -glutamyl AA-glutamyl AA melewati membran sel dan melepaskan AA ke dalam selProduk lain dikonversi kembali menjadi glutation

Protein metabolism8/9 Essential amino acids: must eat them!Transamination: use the essential AA to synthesize the others!

Protein metabolismAnother route:Intestinal bacteria -> ammonia (toxic) -> liver uses it to make amino acids

Protein metabolismAmino acids: C, H, O plus amine group with N

Healthy adult: ingest N=excrete N (turnover of proteins!)

Protein metabolismAmino acids are broken down into:a) ammonia -> ureab) pyruvate or molecules that are part of the krebs cycle -> respired for energy, or converted to fats or glucose

Glucogenic Amino AcidsMetabolized to a-ketoglutarate, pyruvate, oxaloacetate, fumarate, or succinyl CoA Aspartate Asparagine Arginine Phenylalanine Tyrosine Isoleucine Methionine Valine Glutamine Glutamate Proline Histidine Alanine Serine Cysteine Glycine Threonine Tryptophan

Ketogenic Amino AcidsMetabolized to acetyl CoA or acetoacetate Isoleucine Leucine Threonine Tryptophan Lysine Phenylalanine Tyrosine

Katabolisme kerangka karbon pada asam aminoKalau AA tdp melebihi kebutuhan metabolik, kerangka karbonnya akan dikatabolisasi menjadi senyawa antara sebagai sumber energi, atau sebagai substrat bagi sintesis KH, lipidGlikogenik: Ala, Arg, Asp, Cys, Glu, Gly, His, Hyp, Met, Pro, Ser, Thr, ValKetogenik: LeuGlikogenik dan ketogenik: Ile, Lys, Phe, Trp, Tyr

Keseimbangan nitrogenMengacu pada perbedaan asupan total nitrogen dengan kehilangan nitrogen melalui feses, urin, keringatKeseimbangan nitrogen positif: konsumsi nitrogen dengan jumlah yang lebih banyak drpd jumlah yang diekskresikanProtein diuraikan dengan kecepatan yang berbeda-bedaBinatang mengekskresikan nitrogen sebagai hasil akhirnya berupa amonia, asam urat atau urea

Siklus ureaUrea merupakan produk akhir katabolisme nitrogen pada manusia, disintesis dari amonia, CO2, dan nitrogen amida aspartatKarena sintesis urea mengubah amonia yang toksik menjadi urea yang non toksik, semua defek pada sintesis urea akan mengakibatkan intoksikasi amonia.

Kelainan pada siklus ureaGejala klinis: mual, muntah terhadap makanan berprotein tinggi, iritabilitas, letargia, retardasi mental. Kelainan berupa : hiperamonemia, sitrulinemia, hiperargininemia, arginosuksinikasiduria

Defisiensi asam aminoDef. asam amino essensial Kwashiorkor: kadar protein plasma rendah, edema, diare, peningkatan resiko infeksiMarasmus : kekurangan kalori dan protein

Amino Acids Formed From a-KetoglutarateTransamination or Glutamate dehydrogenasea-Keto-glutarateGlutamateGlutamineGlutamine synthase4 StepsProlineOrnithine5 StepsArginineUrea CycleGuanidino group

GABA FormationGlutamateGamma-aminobutyrate(GABA)GABA is an important inhibitory neurotransmitterin the brainDrugs (e.g., benzodiazepines) that enhance the effectsof GABA are useful in treating epilepsy GlutamatedecarboxylaseCO2

Arginine Synthesis: The Urea CycleNH4+ + HCO3- NH2CO2PO3-2GlutamateN-AcetylglutamateOrnithineN-AcetylglutamatesynthaseCoASAc4 StepsCPS-IOrnithine Transcarbamoylase (OTC)(mitochondria)CitrullineUreido groupCarbamoyl phosphateActivates

The Urea Cycle (Contd.)CitrullineArginosuccinateArginosuccinatesynthaseArginineOrnithineFumarateTCA CycleArginaseH2NCONH2UreaArgino-succinaseOrnithineTranscarbamoylase(mitochondria)Asp

Urea FormationOccurs primarily in liver; excreted by kidneyPrincipal method for removing ammoniaHyperammonemia:Defects in urea cycle enzymes (CPS, OTC, etc.)Severe neurological defects in neonatesTreatment: Stop protein intakeDialysisIncrease ammonia excretion: Na benzoate, Na phenylbutyrate, L-arginine, L-citrulline

Blood Urea NitrogenNormal range: 7-18 mg./dLElevated in amino acid catabolism Glutamate N-acetylglutamate CPS-1 activationElevated in renal insufficiencyDecreased in hepatic failure

Formation of SerineGlucoseGlycolysis3-Phospho-glycerate3-Phospho-hydroxypyruvate3-PhosphoserineSerine (Ser)PyruvateDehydrogenaseNAD+ NADH + H+Glutamatea-KetoglutarateTransaminasePhosphatase3 StepsInhibits

Conversion of Serine to GlycineFolateTetrahydrofolate (FH4)Dihydrofolate reductaseN5, N10-Methylene FH4SerineGlycineSerine hydroxymethyltransferase (PLP-dep.)Key intermediatein biosynthesis ofpurines andformation ofthymineImportant in biosynthesis of heme,porphyrins, and purines

Sulfur-Containing Amino AcidsMethionine(Essential)L-HomocysteineMethionineSynthase(Vit. B12-dep.)+ FH4+ 5-Methyl FH4SerineCystathionineCystathionineb-synthase(PLP-dep.)CystathioninelyaseCysteine(Non-essential)+b-Hydroxy-butyrate

HomocysteineHomocysteinuria Rare; deficiency of cystathionine b-synthase Dislocated optical lenses Mental retardation Osteoporosis Cardiovascular disease death

High blood levels of homocysteine associated withcardiovascular disease May be related to dietary folate deficiency Folate enhances conversion of homocysteine to methionine

Methionine Metabolism: Methyl DonationS-Adenosyl methioninesynthaseATPS-Adenosyl Methionine(SAM)S-Adenosyl homocysteineMethyl-transferasesDecarboxylated SAMSAM DecarboxylaseCO2MethionineR-HR-CH3+

Polyamine BiosynthesisOrnithine(from urea cycle)PutrescineCO2Ornithinedecarboxylase(ODC)(PLP-dep.)DecarboxylatedSAMSpermidine synthase5-Methylthio-adenosineSpermidineSpermineDecarboxylatedSAMSpermine synthase5-Methylthio-adenosine

Polyamines Spermidine and spermine found in virtually all procaryotic and eucaryotic cells

Precise role undefined Bind to nucleic acids

Inhibition of biosynthetic pathway:a-Difluoromethyl-ornithine (DFMO)(Eflornithine) - inhibits ODC;used to treatPneumocystis carinii infectons

Creatine and CreatinineArginineGlycine OrnithineArginine-glycinetransamidinase(Kidney)GuanidoacetateGuanidoacetateMethyltransferase(Liver)SAM + ATP

S-Adenosyl-homocysteine + ADPPhosphocreatineCreatinine(Urine)Non-enzymatic(Muscle)Creatine kinase(Muscle)ATPCreatineADP + Pi

Creatine and Creatinine Creatine: Dietary supplement Used to improve athletic performance

Creatinine: Urinary excretion generally constant; proportional to muscle mass

Creatinine Clearance Test: Compares the level of creatinine in urine (24 hrs.) with the creatinine level in the blood Used to assess kidney function Important determinant in dosing of several drugs in patients with impaired renal function

Histidine Metabolism: Histamine FormationHistidineHistamineHistidinedecarboxylaseCO2Histamine: Synthesized in and released by mast cells Mediator of allergic response: vasodilation, bronchoconstriction (H1 receptors) H1 blockers: Diphenhydramine (Benadryl) Loratidine (Claritin) Stimulates secretion of gastric acid (H2 receptors) H2 blockers: Cimetidine (Tagamet); ranitidine (Zantac)

Phenylalanine and TyrosinePhenylalanine(Essential)Tyrosine(Non-essential)Phenylalanine-4-Monooxygenase(Phenylalaninehydroxylase)O2H2O++NADPH + H+NADP+TetrahydrobiopterinDihydrobiopterin

Phenylketonuria (PKU) DiseaseDeficiency of Phe hydroxylaseOccurs in 1:16,000 live births in U.S.Seizures, mental retardation, brain damageTreatment: limit phenylalanine intakeScreening of all newborns mandated in all statesPheTyrTransaminationPhenylpyruvate(urine)

Catecholamine BiosynthesisTyr hydroxylaseO2TyrosineDihydroxyphenylalanine (DOPA)DopamineDOPAdecarboxylaseCO2DopaminehydroxylaseNorepinephrineCatecholEpinephrine(Adrenaline)SAMS-Adenosyl-homocysteineMethyl transferaseDOPA, dopamine, norepinephrine,and epinephrine are all neurotransmitters

L-DOPA in ParkinsonismBlood BrainBloodBrain BarrierL-DOPAL-DOPA DopamineDopamineCarbidopaBlocksParkinsonism associated with dopamine in brain through loss ofneurons in basal ganglia.Carbidopa + L-DOPA

Melanin FormationHighly colored polymeric intermediatesMelanin(Black polymer)TyrosinaseDOPADopaquinoneTyrosineTyrosinaseMelanin formed in skin (melanocytes), eyes, and hairIn skin, protects against sunlightAlbinism: genetic deficiency of tyrosinase

Tryptophan Metabolism: Serotonin FormationTryptophan(Trp)Indole ringTrphydroxylaseO25-Hydroxy-tryptophanDecarboxylaseCO25-Hydroxy-tryptamine (5-HT);Serotonin

Serotonin Serotonin formed in: Brain (neurotransmitter; regulation of sleep, mood, appetite) Platelets (platelet aggregation, vasoconstriction) Smooth muscle (contraction) Gastrointestinal tract (enterochromaffin cells - major storage site)

Drugs affecting serotonin actions used to treat: DepressionSerotonin-selective reuptake inhibitors (SSRI) Migraine Schizophrenia Obsessive-compulsive disorders Chemotherapy-induced emesis

Some hallucinogens (e.g., LSD) act as serotonin agonists

Food supplement promoted for serotonin effects L-Tryptophan disaster (1989): Eosinophilia-myalgia syndrome (EMS) Severe muscle and joint pain Weakness Swelling of the arms and legs Fever Skin rash Eosinophilia Many hundreds of cases; several deaths Traced to impurities L-Tryptophan

Serotonin Metabolism: 5-HIAASerotoninMAODehydrogenase5-Hydroxyindole acetic acid (5-HIAA) (Urine)Carcinoid tumors: Malignant GI tumor type Excretion of large amounts of 5-HIAA

Serotonin Metabolism: Melatonin2 StepsSerotoninMelatoninMelatonin: Formed principally in pineal gland Synthesis controlled by light, among other factors Induces skin lightening Suppresses ovarian function Possible use in sleep disorders

Tryptophan Metabolism:Biosynthesis of Nicotinic AcidTryptophanNicotinic acid (Niacin)Several stepsNicotinamide adenine dinucleotide (NAD)

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