Amino Acids in Biochemistry

Marks' Basic Medical Biochemistry

• This is a textbook on basic medical biochemistry, intended as a clinical approach.
• It is in its 5th edition.
• The authors are Michael Lieberman and Alisa Peet.
• The publisher is Wolters Kluwer.

Amino Acid and Protein

• Amino acids are the building blocks of proteins.
• Proteins are essential for all life processes, including growth, digestion, feeding, DNA replication, and movement.
• Every body part contains proteins.

Properties of Amino Acids

• General properties: amino acids have an amino group, a carboxyl group, a chiral carbon, and an R-group.
• Side-chain properties: amino acids have different side chains, which can be grouped into non-polar, aliphatic; uncharged polar; acidic, basic.
• Nutritionally essential amino acids: nine amino acids that cannot be synthesized in the body and must be obtained from the diet. Examples include phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, leucine, and lysine. Some amino acids are also considered semi-essential, meaning they are essential during growth.

General Structure of an Amino Acid

• Amino group (+H₃N)
• Carboxyl group (-COOH)
• Chiral carbon
• R-group: a side chain (20 different types)

Configurations of Amino Acids (L and D)

• L-amino acids are predominantly found in proteins.
• D-amino acids are found in certain organisms and peptides.

Side Chain Properties (Grouping)

• Non-polar, aliphatic
• Uncharged polar
• Acidic
• Basic
• Sulfur-containing
• Aromatic ring containing (two or more categories)

Non-polar (Hydrophobic) amino acids

• Include valine, isoleucine, leucine, methionine, phenylalanine, tryptophan, alanine, proline, and glycine.
• Hydrophobic, meaning they avoid water.
• Often found embedded in cell membranes.

Uncharged polar amino acids

• Include serine, threonine, tyrosine, asparagine, glutamine, cysteine, and histidine.
• Water-soluble due to hydroxyl (-OH) or amide (-NH₂) groups.
• Many are involved in phosphorylation, a vital cellular process.

Acidic and Basic amino acids (charged amino acids)

• Includes Aspartate, Glutamate, Arginine, Lysine, and Histidine.
• Acidic amino acids have negatively charged side chains (Asp, Glu).
• Basic amino acids have positively charged side chains (Arg, Lys, His).

Sulfur-containing amino acids

• Include methionine and cysteine.
• Cysteine has a thiol group (-SH), that can form disulfide bonds, which are crucial for protein structure.

Aromatic ring amino acids

• Include phenylalanine, tyrosine, and tryptophan.
• The aromatic rings give these amino acids unique properties.

Nutritionally Essential Amino Acids

• Nine essential amino acids that the body cannot synthesize and must be obtained from the diet.
• Examples include phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, leucine, and lysine. Also, histidine is semi-essential.

Conditional Essential Amino Acids

• Amino acids that are essential under specific conditions (e.g., disease states or rapid growth).
• Examples include cysteine, tyrosine, arginine, proline, and glycine.

Quality of Dietary Protein

• The quality of protein depends on the presence of essential amino acids in adequate amounts.
• Animal proteins (meat, milk, eggs) generally contain all essential amino acids.

Kwashiorkor and Marasmus

• Kwashiorkor is a disease caused by a protein deficiency.
• Marasmus is a disease resulting from inadequate intake of protein and energy.
• Symptoms and signs are shown (distended abdomen, swollen ankles, wrinkled/scaly skin, etc).

MCQ True/False Questions

• Provided a collection of true/false questions about amino acids.

Summary of Amino Acids

• Hierarchical outline representing amino acids with a main classification structure (general structure, side chain properties, acid-base properties, list of essential, conditional amino acids) to help understand the characteristics of amino acids.