AMINO ACIDS AND PROTEINS Flashcards by LEA ROS MANALASTAS

Polymers of amino acids

Proteins

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Number of naturally occurring amino acids

300

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number of constitute the monomer units of proteins

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Definition of Amino Acids

▪ Building blocks of proteins
▪ Determine the biologic activity of the protein
▪ Growth, repair, and maintenance of all cells
▪ Synthesis of body proteins
▪ Synthesis of non-protein nitrogen-containing compounds

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Classification of Amino Acids

Nutritional Perspective
Metabolic Fate
Polarity
Structure of the Side Chain
pH

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number of nutritionally non—essential – produced during glycolysis and of the citric acid cycle

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Provides all essential amino acids

Complete protein

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Deficient in one or more of the essential amino acids

Incomplete proteins

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Missing: Rice, corn, and wheat

lysine

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Missing: threonine

Rice

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Missing: tryptophan

corn

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Deficient: methionine

Beans, peas, and other legumes

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Body does not synthesize them and must be supplied through the diet

Essential or indispensable amino acids

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_________ is produced from phenylalanine

Tyrosine

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Tyrosine is produced from _________

phenylalanine

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Conditionally essential and supplied exogenously to specific populations

Semi–essential amino acids

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________ and ________ can be synthesized by adults and not by growing
children

arginine and histidine

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body can synthesize _________ amino acids to meet the biological needs

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Essential Amino Acids

Arginine
Histidine
Methionine
Isoleucine
Phenylalanine
Threonine
Tryptophan
Leucine
Lysine
Valine

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Non-Essential Amino Acids

Alanine
Asparagine
Aspartic Acid
Glutamic Acid
Glycine
Glutamine
Proline
Cysteine
Serine
Tyrosine

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Has both anabolic and catabolic processes

amphibolic

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_________ amino acids can not be stored and thus are catabolized (metabolized)

Excess

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Generate precursors of glucose or glycogen

Glucogenic amino acids

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Glucogenic amino acids Precursors:

pyruvate or a citric acid cycle intermediate

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Alanine deaminated to _________

pyruvate

_________ deaminated to pyruvate

Alanine

Arginine converted to __________

α-ketoglutarate

__________ converted to α-ketoglutarate

Arginine

Aspartate converted to _________

oxaloacetate

_________ converted to oxaloacetate

Aspartate

Can be converted into fat (fat producing) or Acetyl CoA

Ketogenic amino acids

_______ can be synthesized from amino acids

Fat

Ketogenic amino acids Generate ________

ketone bodies

Generate precursors of both glucose and fats

Glucogenic and Ketogenic amino acids

Class of inherited errors of metabolism where There is an enzyme defect that inhibits the body’s ability to metabolize certain amino acids

Aminoacidopathies

defined the concept of inborn errors of metabolism

1909 Garrod

concept of inborn errors of metabolism:

▪ Blocks in specific metabolic pathways result from defects in particular enzymes ▪Defective or absent protein is an enzyme

Probable reasons of aminoacidopathies:

A. Activity of a specific enzyme in the metabolic pathway B. Membrane transport system for amino acids

Aminoacidopathies

Phenylketonuria PKU Tyrosinemia Maple Syrup Urine Disease MSUD Alkaptonuria (Black urine disease) Cystinuria (Hartnup’s Disease)

Phenylalanine hydroxylase (PAH) deficiency

Phenylketonuria PKU

First newborn screening test introduced

(early 1960s)

an absence of activity of the enzyme phenylalanine hydroxylase (PAH), which catalyzes the conversion of phenylalanine to tyrosine

Phenylketonuria Mechanism

Chronically high levels of phenylalanine results to

brain problems

Hyperphenylalaninemia cases that are not the result of the lack of the PAH enzyme

Deficiency in the enzymes for regeneration and synthesis of tetrahydrobiopterin (BH4)

cofactor for enzymatic hydroxylation of the aromatic amino acids

BH4

Phenylketonuria Absence of enzyme:

Phenylalanine levels = >1,200 μmol/L Newborn: upper limit of normal = 120 μmol/L (2 mg/dL) Metabolites: blood and urine (characteristic musty odor)

Women with PKU (untreated during pregnancy):

microcephalic and mentally retarded babies

(Phenylketonuria) Insufficient synthesis of _________

serotonin

is the pigment synthesized from tyrosine by tyrosinase:

Melanin

Phenylketonuria Management

Sapropterin dihydrochloride (Kuvan®) Reduce phenylalanine levels by increasing the activity of the PAH enzyme

Phenylketonuria Management 2

Pegvaliase-PQPZ (Palynziq®) First FDA-approved enzyme substitution therapy as of 2018, substitutes a PEGylated version of the enzyme phenylalanine ammonia lyase for the deficient PAH enzyme

Phenylketonuria Management 3

Dietary restriction of phenylalanine with tyrosine supplementation

Characterized by the excretion of tyrosine and tyrosine catabolites in urine

Tyrosinemia

Tyrosinemia Most severe form Low levels of the enzyme fumarylacetoacetate hydrolase

Type I

Type I Tyrosinemia

Leads to liver and kidney failure, problems affecting the nervous system, and an increased risk of cirrhosis or liver cancer

Type I Tyrosinemia Management 1

Nitisinone (also known as NTBC) In act on tyrosine metabolism upstream of the defect to prevent the production of these metabolites.

Type I Tyrosinemia Management

Diet prescribed a low-phenylalanine, low tyrosine diet

AKA Richner-Hanhart syndrome deficiency of the enzyme tyrosine aminotransferase:

Type II Tyrosinemia

Type II Tyrosinemia Management

No cure for this condition Some of the symptoms may be managed with a diet:

Rare disorder (only a few cases have been reported) Deficiency of the enzyme 4- hydroxyphenylpyruvate dioxygenase:

Type III Tyrosinemia

Type III Tyrosinemia Clinical Presentation

Mild mental retardation, seizures, and periodic loss of balance and coordination

Type III Tyrosinemia Management

▪ Follow a phenylalanine- and tyrosine-restricted diet ▪ No available treatment yet

Defective enzyme: homogentisate oxidase in tyrosine metabolism Homogentisate accumulates in tissues and blood → excreted into urine

Alkaptonuria

Alkaptonuria Clinical Presentation

Ochronosis:, Arthritis, Signs of aortic or mitral valvulitis

Alkaptonuria Management

➢Ascorbic Acid ➢ Nitisinone

Absence or greatly reduced activity of the enzyme branched-chain α-ketoacid dehydrogenase → blocking normal metabolism of leucine, isoleucine, and valine

Maple Syrup Urine Disease (MSUD)

Degradation of the branched-chain amino acids:

➢ Valine → propionyl CoA ➢ Isoleucine → propionyl CoA and acetyl CoA ➢ Leucine → acetoacetate and acetyl CoA

Maple Syrup Urine Disease (MSUD) Clinical Presentation

Characteristic maple syrup or burnt sugar odor: urine, breath, and skin.

Maple Syrup Urine Disease (MSUD) Management

▪Thiamine ▪ Dietary restriction of branched-chain AA

Amino acid transport disorder Defective transport of cystine and basic amino acids across renal tubule and the small intestine.

Cystinuria

Cystinuria Clinical Presentation

▪ Formationof cystine stones in the kidney, due to its low solubility ▪ Chronic urinary tract infections ▪ Hematuria and dysuria

Cystinuria Management

▪ Hydration ▪ Urinary Alkalinizers ▪ Chelating Agents ▪Crystal Growth Inhibitors

to decrease urinary cystine concentration

Hyperdiuresis

Urinary Alkalinizers

➢ Potassium Citrate, Acetazolamide