Related Subjects:
|Protein metabolism
|Protein Synthesis
|Amino acids
|Human Metabolism
Overview of Amino Acids
Amino acids are the building blocks of proteins, playing crucial roles in various physiological processes. There are 20 standard amino acids, each with a unique side chain that determines its properties and functions.
Structure of Amino Acids
- All amino acids share a common structure:
- An amino group (-NH2).
- A carboxyl group (-COOH).
- A hydrogen atom.
- A distinctive side chain (R group) that varies among different amino acids.
- The central carbon to which these groups are attached is known as the alpha carbon.
Classification of Amino Acids
- By Polarity and Charge:
- Nonpolar (Hydrophobic):
- Glycine (Gly, G)
- Alanine (Ala, A)
- Valine (Val, V)
- Leucine (Leu, L)
- Isoleucine (Ile, I)
- Proline (Pro, P)
- Methionine (Met, M)
- Phenylalanine (Phe, F)
- Tryptophan (Trp, W)
- Polar (Hydrophilic):
- Serine (Ser, S)
- Threonine (Thr, T)
- Cysteine (Cys, C)
- Tyrosine (Tyr, Y)
- Asparagine (Asn, N)
- Glutamine (Gln, Q)
- Charged:
- Acidic (negatively charged):
- Aspartic acid (Asp, D)
- Glutamic acid (Glu, E)
- Basic (positively charged):
- Lysine (Lys, K)
- Arginine (Arg, R)
- Histidine (His, H)
- By Nutritional Requirement:
- Essential Amino Acids (cannot be synthesized by the body and must be obtained from the diet):
- Histidine (His, H)
- Isoleucine (Ile, I)
- Leucine (Leu, L)
- Lysine (Lys, K)
- Methionine (Met, M)
- Phenylalanine (Phe, F)
- Threonine (Thr, T)
- Tryptophan (Trp, W)
- Valine (Val, V)
- Non-Essential Amino Acids (can be synthesized by the body):
- Alanine (Ala, A)
- Asparagine (Asn, N)
- Aspartic acid (Asp, D)
- Glutamic acid (Glu, E)
- Serine (Ser, S)
- Conditionally Essential Amino Acids (normally synthesized by the body but may need to be supplemented in certain conditions):
- Arginine (Arg, R)
- Cysteine (Cys, C)
- Glutamine (Gln, Q)
- Glycine (Gly, G)
- Proline (Pro, P)
- Tyrosine (Tyr, Y)
Functions of Amino Acids
- Protein Synthesis:
- Amino acids are the building blocks of proteins, which are essential for the structure, function, and regulation of the body's tissues and organs.
- Enzyme Activity:
- Many enzymes, which catalyze biochemical reactions, are proteins made up of amino acids.
- Hormone Production:
- Certain amino acids are precursors to hormones. For example, tyrosine is a precursor to thyroid hormones and catecholamines.
- Immune Function:
- Amino acids are vital for the synthesis of antibodies and other immune proteins.
- Neurotransmitter Synthesis:
- Amino acids such as tryptophan and tyrosine are precursors to neurotransmitters like serotonin and dopamine.
- Energy Production:
- Amino acids can be used as a source of energy, especially during periods of fasting or intense physical activity.
Metabolism of Amino Acids
- Transamination:
- Transfer of an amino group from an amino acid to a keto acid, producing a new amino acid and a new keto acid.
- Important for the synthesis of non-essential amino acids.
- Deamination:
- Removal of an amino group from an amino acid, producing ammonia and a keto acid.
- Ammonia is converted to urea in the liver and excreted in the urine.
- Decarboxylation:
- Removal of a carboxyl group from an amino acid, producing an amine and CO2.
- Important for the synthesis of neurotransmitters.
Clinical Relevance
- Amino Acid Deficiencies:
- Deficiencies in essential amino acids can lead to various health issues, including impaired growth, weakened immune function, and muscle wasting.
- Inborn Errors of Metabolism:
- Genetic disorders affecting amino acid metabolism can lead to conditions such as phenylketonuria (PKU) and maple syrup urine disease.
- Protein-Energy Malnutrition:
- Severe deficiency of protein and energy can result in conditions such as kwashiorkor and marasmus.
- Clinical Use of Amino Acids:
- Amino acid supplements are used in medical nutrition therapy for conditions like liver disease, renal failure, and recovery from surgery or trauma.
Summary
Amino acids are fundamental molecules essential for protein synthesis, enzyme activity, hormone production, immune function, neurotransmitter synthesis, and energy production. They can be classified based on their polarity, charge, and nutritional requirement. Understanding amino acid metabolism and their clinical relevance is crucial for diagnosing and managing various health conditions.