Phenylalanine Metabolism in Humans
The metabolism of the aromatic amino acids-phenylalanine and tyrosine in man provides a best example of a gene-controlled, enzyme catalyzed biochemical reaction. In man, phenylalanine is an essential amino acid which must be supplied in the dietary proteins. Once in the body, phenylalanine may follow any of three paths. It may be (1) incorporated into cellular proteins, (2) converted to phenylpyruvic acid, or (3) converted to tyrosine. The conversion of phenylalanine into tyrosine takes place in the presence of phenylalanine hydroxylase enzyme, in the liver cells. Tyrosine is converted in turn to 3-4-dihydroxy phenylalanine (nick-named DOPA) by another enzyme and DOPA serves as a precursor for the hormones adrenaline and noradrenaline and for the black pigment, melanin.
Tyrosine itself serves as a precursor of the hormones thyroxine and triiodothyronine. Excess tyrosine is degraded to carbon dioxide and water by a series of steps which involves the formation of p-hydroxyphenyl pyruvate, 2-5 dihydroxy phenyl pyruvate, homogentisic acid, maleylacetoacetic acid, fumaryl acetoacetic acid and fumaric and acetoacetic acid. Excess phenylalanine is degraded by a series of steps to compounds which include phenylpyruvic acid and phenyl lactic acid.
Genetic disorders of the phenylalanine metabolism and resulted diseases-Five rare diseases in man result from improper functioning of five enzyme systems (i.e., metabolic blocks) involved in the metabolism of phenylalanine, tyrosine and their derivatives. All of these diseases have been found to be due to mutant, autosomal recessive genes in homozygous conditions. These diseases are following:
1.Phenylketonuria-Persons with genotype pp fail to produce enzyme phenylalanine hydroxylase (parahydroxylase) with the result that phenylalanine fails to convert into tyrosine and consequently, the concentration of phenylalanine rises in the blood plasma, cerebrospinal fluid and urine. The urine of phenylketonuric (PKUJ patient contains (in addition to phenylalanine) elevated amounts of phenylpyruvic acid, phenyl lactic acid and other derivatives of phenylalanine. PKU patients have light pigmentation and are physically and mentally retarded. The feeble mindedness in PKU patients is thought to -be due to an impairment of the brain tissues by the phenylpyruvic acid in the cerebro-spinal fluid.
2. Alkaptonuria- The persons with genotype hh fail to produce the enzyme homogentisic acid oxidase which catalyzes the oxidation of homogentisic acid. Therefore, in them, normal oxidation of homogentisic acid into water and carbon dioxide does not occur and large amounts of homogentisic acid are excreted in the urine, which turn black upon exposure to the air. Moreover, the homogentisic acid accumulate in the body and become attached to the collagen of cartilage and other connective tissues, due to which, the ear and sclerae are stained black. Persons with such phenotypic abnormalities are said to have alkaptonuria disease.
3. Tyrosinosis-The recessive gene, t in its homozygous condition, blocks the conversion of p-hydroxyphenylpyruvate into 2, S-dihydroxyphenyl pyruvate. This leads to the accumulation of tyrosine, excesses of which are excreted via the urine. This condition is called tyrosinosis. It is reported in only one human and cause no harmful effect.
4. Goitrous cretinism-The persons with cc genotype fail to produce the enzyme which is required for the conversion of tyrosine into thyroxine and triiodothyronine hormones in their thyroid glands. This condition is called goitrous cretinism which is accompanied by a considerable degree of physical and mental retardation and hypertrophy of thyroid gland.
5. Albinism- The persons with recessive AA genotype lack in the tyrosinase enzyme system which is required for the conversion of 3, 4-dihydroxyphenyl alanine (DOPA) into melanin pigment inside the melanocytes. In an albino patient melanocytes are present in normal numbers in their skin, hairs, iris, etc., but lack in melanin pigment.
Digestive System.
Dominant allele disorders are single gene disorders which take effect in the heterozygous state.
humans need proteins to make good muscles and health.
No. In humans there are nine essential amino acids that cannot be synthesized by the human body, and which humans must get in their diet. They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histadine. Other animals may have a different set of essential amino acids. Refer to the Wikipedia article referenced below for more information.Source: https://en.m.wikipedia.org/wiki/Essential_amino_acid
The disorder is controlled by a recessive factor.
Eight amino acids are generally regarded as essential for humans: phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, and lysine. Cysteine (or sulphur-containing amino acids), tyrosine (or aromatic amino acids), histidine and arginine are additionally required by infants and growing children.
The amino acids generally considered "nonessential" for adult humans are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. People with certain disorders may need some of these in their diets. For example, most humans can make tyrosine from phenylalanine, but people with PKU cannot, so it's essential that they get it in their diet.
In humans, the gene that codes for the enzyme phenylalanine hydroxylase is an expmple of a recessive gene
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For most humans that do not have psychological disorders, yes.
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Digestive System.
Digestive System.
In humans it would be the X chromosome.
Humans have two eyes but when people have disorders it may vary.
Dominant allele disorders are single gene disorders which take effect in the heterozygous state.
The primary organ of metabolism in the body is the liver. The liver is responsible for controlling cholesterol metabolism and is the largest internal organ in humans.