The 20 standard amino acids and function plus selenocysteine (Sec)

By SWA

The building blocks of proteins. These amino acids are represented by their three-letter and one-letter abbreviations, as well as their molecular structures. Each amino acid plays a crucial role in the structure and function of proteins, which are essential for many biological processes.

Roles and Functions:

  1. Alanine (Ala, A): A non-polar, aliphatic amino acid involved in metabolism and used as an energy source.
  2. Leucine (Leu, L): A branched-chain amino acid that plays a role in protein synthesis and muscle repair.
  3. Phenylalanine (Phe, F): Aromatic, involved in the production of neurotransmitters and other molecules.
  4. Threonine (Thr, T): Polar, involved in protein synthesis and maintaining protein structure.
  5. Cysteine (Cys, C): Contains a sulfur atom, forms disulfide bonds crucial for protein folding.
  6. Arginine (Arg, R): Positively charged, important for the urea cycle and nitric oxide production.
  7. Aspartic Acid (Asp, D): Negatively charged, involved in energy production and metabolism.
  8. Valine (Val, V): Branched-chain amino acid, helps stimulate muscle growth and tissue repair.
  9. Methionine (Met, M): Sulfur-containing, important for initiating protein synthesis.
  10. Tryptophan (Trp, W): Aromatic, precursor to serotonin, a neurotransmitter.
  11. Asparagine (Asn, N): Polar, helps in protein stability and function, involved in nitrogen metabolism.
  12. Selenocysteine (Sec, U): Similar to cysteine, but with selenium instead of sulfur, part of enzymes that protect against oxidative damage.
  13. Histidine (His, H): Positively charged, plays a role in enzyme active sites and is a precursor to histamine.
  14. Glutamic Acid (Glu, E): Negatively charged, involved in neurotransmission and energy metabolism.
  15. Isoleucine (Ile, I): Branched-chain, helps regulate blood sugar levels and muscle metabolism.
  16. Proline (Pro, P): Non-polar, involved in the stability and structure of proteins, especially in turns.
  17. Serine (Ser, S): Polar, plays a role in metabolism and protein phosphorylation.
  18. Glutamine (Gln, Q): Polar, important for nitrogen transport and immune system function.
  19. Tyrosine (Tyr, Y): Aromatic, precursor to hormones like dopamine and thyroid hormones.
  20. Lysine (Lys, K): Positively charged, essential for protein synthesis and tissue repair.
  21. Glycine (Gly, G): The smallest amino acid, crucial for protein flexibility and collagen formation.

These amino acids combine in various sequences to form proteins, which are vital for virtually all biological processes, including structural roles, enzymatic activity, signal transduction, and more.

Here's a more detailed explanation of the roles and functions of each amino acid, along with links to additional information.

1. Alanine (Ala, A)

  • Role: Alanine is a non-polar, aliphatic amino acid that plays an important role in glucose metabolism and energy production. It is used by muscles as an energy source during exercise and is involved in the gluconeogenesis process, where it helps generate glucose from non-carbohydrate sources.
  • Function: Serves as a carrier of nitrogen from tissues to the liver for excretion.
  • More on Alanine

2. Leucine (Leu, L)

  • Role: Leucine is a branched-chain amino acid (BCAA) critical for protein synthesis and muscle repair. It activates the mTOR pathway, which regulates cell growth and protein production.
  • Function: Essential for muscle growth, repair, and overall anabolism.
  • More on Leucine

3. Phenylalanine (Phe, F)

  • Role: This aromatic amino acid is a precursor for several neurotransmitters, including dopamine, norepinephrine, and epinephrine. It is also important for the synthesis of melanin (skin pigment).
  • Function: Involved in neurotransmitter production and mood regulation.
  • More on Phenylalanine

4. Threonine (Thr, T)

  • Role: Threonine is a polar amino acid important in protein structure, especially collagen and elastin. It's also involved in immune function.
  • Function: Plays a role in maintaining protein structure and integrity, and assists in fat metabolism in the liver.
  • More on Threonine

5. Cysteine (Cys, C)

  • Role: Cysteine contains sulfur, which allows it to form disulfide bonds that help stabilize protein structures. It is also a precursor to the antioxidant glutathione.
  • Function: Important for maintaining protein structure and for antioxidant defense.
  • More on Cysteine

6. Arginine (Arg, R)

  • Role: Arginine is essential for producing nitric oxide, which helps dilate blood vessels. It's also important for the urea cycle, helping to detoxify ammonia.
  • Function: Plays a key role in wound healing, immune function, and hormone release.
  • More on Arginine

7. Aspartic Acid (Asp, D)

  • Role: Aspartic acid is negatively charged and is involved in energy production through the citric acid cycle. It also serves as a precursor for other amino acids and nucleotides.
  • Function: Participates in biosynthetic pathways, neurotransmission, and urea cycle.
  • More on Aspartic Acid

8. Valine (Val, V)

  • Role: A branched-chain amino acid important for muscle metabolism and tissue repair. Valine also helps maintain nitrogen balance in the body.
  • Function: Provides energy for muscle tissues and helps with tissue repair and growth.
  • More on Valine

9. Methionine (Met, M)

  • Role: Methionine contains sulfur and is crucial for starting the synthesis of proteins. It also plays a role in methylation, which is important for gene expression.
  • Function: Acts as the initiating amino acid in protein synthesis and is a precursor for the antioxidant glutathione.
  • More on Methionine

10. Tryptophan (Trp, W)

  • Role: Tryptophan is an essential amino acid and a precursor for serotonin, a neurotransmitter that regulates mood, sleep, and appetite.
  • Function: Important for mental health, sleep regulation, and mood control.
  • More on Tryptophan

11. Asparagine (Asn, N)

  • Role: Asparagine is a polar amino acid important for protein stability and synthesis, and is involved in metabolic control and ammonia detoxification.
  • Function: Helps in maintaining protein structure and function, especially in the nervous system.
  • More on Asparagine

12. Selenocysteine (Sec, U)

  • Role: Known as the 21st amino acid, selenocysteine contains selenium instead of sulfur and is important for the catalytic activity of certain enzymes involved in antioxidant defense.
  • Function: Found in selenoproteins that help protect against oxidative stress.
  • More on Selenocysteine

13. Histidine (His, H)

  • Role: Histidine is a positively charged amino acid that acts as a precursor for histamine, a compound involved in immune responses, gastric acid secretion, and neurotransmission.
  • Function: Crucial for immune function and enzyme activity.
  • More on Histidine

14. Glutamic Acid (Glu, E)

  • Role: Glutamic acid acts as a neurotransmitter in the brain and is involved in synaptic plasticity. It is also a key player in the Krebs cycle for energy production.
  • Function: Important for brain function, cellular metabolism, and detoxification.
  • More on Glutamic Acid

15. Isoleucine (Ile, I)

  • Role: Another branched-chain amino acid, isoleucine plays a role in muscle metabolism and energy regulation, especially during physical activity.
  • Function: Supports immune function, hemoglobin production, and muscle metabolism.
  • More on Isoleucine

16. Proline (Pro, P)

  • Role: Proline is unique because it is a cyclic amino acid that provides structural stability to proteins, particularly in collagen.
  • Function: Critical for the stability and folding of proteins.
  • More on Proline

17. Serine (Ser, S)

  • Role: Serine is a polar amino acid involved in metabolism and protein phosphorylation. It is also involved in the synthesis of phospholipids and is important for brain function.
  • Function: Involved in metabolism, enzyme regulation, and the synthesis of proteins and phospholipids.
  • More on Serine

18. Glutamine (Gln, Q)

  • Role: Glutamine is the most abundant amino acid in the body and is important for nitrogen transport and maintaining a healthy immune system.
  • Function: Critical for immune function, nitrogen transport, and intestinal health.
  • More on Glutamine

19. Tyrosine (Tyr, Y)

  • Role: Tyrosine is a precursor to neurotransmitters like dopamine, norepinephrine, and epinephrine, as well as hormones like thyroid hormones.
  • Function: Important for mental health, stress response, and metabolic regulation.
  • More on Tyrosine

20. Lysine (Lys, K)

  • Role: Lysine is essential for protein synthesis, tissue repair, and the production of enzymes and hormones. It also helps with calcium absorption.
  • Function: Important for muscle repair, growth, and calcium homeostasis.
  • More on Lysine

21. Glycine (Gly, G)

  • Role: Glycine is the smallest amino acid and is involved in the synthesis of proteins, DNA, and neurotransmitters. It also plays a role in collagen formation.
  • Function: Acts as a neurotransmitter and is crucial for tissue repair and collagen stability.
  • More on Glycine

Each of these amino acids is vital for the complex functions of proteins, which serve as enzymes, signaling molecules, structural components, and more. For a deeper dive into the chemistry and biological importance of each, visit their respective links!

© 2000-2025 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a fife year copy right.
Library of Congress Card Number: LCN 00-192742 ISBN: 0-9703195-0-9



 


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