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NEET MDS Exam Preparation – BIOCHEMISTRY
SUBJECT: BIOCHEMISTRY
Topic: SOME IMPORTANT AMINO ACIDS
Amino acids are considered to be the monomers of proteins. Structurally, they consist of an amino group (-NH2), a carboxylic group (-COOH) (hence the name) along with a side chain (-R) specific to each amino acid. They can be classified based on the differences in their side chains into aliphatic, aromatic, sulphur containing, acidic, basic etc. For example, aliphatic amino acids are valine, leucine and isoleucine. They are also called branched-chain amino acids (BCAA).
There are 20 different amino acids that combine to create an array of versatile proteins. Based on the ability of the body to synthesize, amino acids can be classified into essential, semi-essential and non-essential. All the amino acids except glycine are chiral molecules. They exist in two optically active forms that are mirror images of each other, designated as D and L forms.
Some important amino acids are,
Glycine: It is the simplest amino acid and hence is optically inactive. Glycine plays a role in the synthesis of purine, heme, glutathione, serine, creatine etc. Glycine has two neurotransmitter roles in the central nervous system, one inhibitory and one excitatory.
Creatine: Creatine is formed from Glycine, arginine and methionine. It undergoes spontaneous cyclization to form anhydride form creatinine, which is excreted in urine
Tryptophan: It is the first identified essential amino acid. Tryptophan acts as the precursor for the co enzymes of niacin (NAD+, NADP+). Tryptophan is essential for the synthesis of serotonin and melatonin.
Phenylalanine and tyrosine: They are structurally related amino acids. Since phenylalanine is essential while tyrosine is a non-essential amino acid, ingestion of tyrosine reduces the requirement of phenylalanine, which is known as the “Sparing action of tyrosine on Phenylalanine”. Various biologically important compounds are derived from tyrosine. Derivatives of tyrosine are Epinephrine, Norepinephrine, Dopamine, Thyroid hormones and melanin.
Histidine: Histidine forms one-carbon unit (formimino group), which is taken up by tetrahydrofolate (THF) to form formimino THF. This in turn combines with glutamate to form FIGLU. Hence to detect folate deficiency, FIGLU excretion test or Histidine load test can be used.
Non-protein amino acids: Non-protein amino acids are those which are never found in proteins but involved in important functions. A few examples include ornithine, citrulline and arginosuccinic acid involved in urea synthesis, Homocysteine in methionine metabolism etc.
Each protein has unique sequences of amino acids in its configuration. Proteins are virtually required for all cellular processes of normal physiological functioning.
There are 20 different amino acids that combine to create an array of versatile proteins. Based on the ability of the body to synthesize, amino acids can be classified into essential, semi-essential and non-essential. All the amino acids except glycine are chiral molecules. They exist in two optically active forms that are mirror images of each other, designated as D and L forms.
Some important amino acids are,
Glycine: It is the simplest amino acid and hence is optically inactive. Glycine plays a role in the synthesis of purine, heme, glutathione, serine, creatine etc. Glycine has two neurotransmitter roles in the central nervous system, one inhibitory and one excitatory.
Creatine: Creatine is formed from Glycine, arginine and methionine. It undergoes spontaneous cyclization to form anhydride form creatinine, which is excreted in urine
Tryptophan: It is the first identified essential amino acid. Tryptophan acts as the precursor for the co enzymes of niacin (NAD+, NADP+). Tryptophan is essential for the synthesis of serotonin and melatonin.
Phenylalanine and tyrosine: They are structurally related amino acids. Since phenylalanine is essential while tyrosine is a non-essential amino acid, ingestion of tyrosine reduces the requirement of phenylalanine, which is known as the “Sparing action of tyrosine on Phenylalanine”. Various biologically important compounds are derived from tyrosine. Derivatives of tyrosine are Epinephrine, Norepinephrine, Dopamine, Thyroid hormones and melanin.
Histidine: Histidine forms one-carbon unit (formimino group), which is taken up by tetrahydrofolate (THF) to form formimino THF. This in turn combines with glutamate to form FIGLU. Hence to detect folate deficiency, FIGLU excretion test or Histidine load test can be used.
Non-protein amino acids: Non-protein amino acids are those which are never found in proteins but involved in important functions. A few examples include ornithine, citrulline and arginosuccinic acid involved in urea synthesis, Homocysteine in methionine metabolism etc.
Each protein has unique sequences of amino acids in its configuration. Proteins are virtually required for all cellular processes of normal physiological functioning.
Questions
1. Which of the following amino acid is the precursor for adrenaline synthesis?
a) Phenylalanine
b) Tyrosine
c) Tryptophan
d) None of the above
2. FIGLU excretion test is done to estimate the deficiency of
a) Vitamin K
b) Vitamin B12
c) Folic acid
d) Niacin
3. In maple syrup urine disease the amino acids excreted in the urine are
a) Leucine
b) Isoleucine
c) Valine
d) All of the above
a) Phenylalanine
b) Tyrosine
c) Tryptophan
d) None of the above
2. FIGLU excretion test is done to estimate the deficiency of
a) Vitamin K
b) Vitamin B12
c) Folic acid
d) Niacin
3. In maple syrup urine disease the amino acids excreted in the urine are
a) Leucine
b) Isoleucine
c) Valine
d) All of the above
Answer
1 - (B)2 - (C)
3 - (D)
