Peptides and Amino Acids Quiz

Peptides

• Peptides are polymers of amino acids.
• Dietary polymers include carbohydrates, proteins, and fats (lipids).
• Monomers are the building blocks of polymers.
• Carbohydrate polymers are broken down in the digestive system into monosaccharides (glucose, fructose, galactose).
• Protein polymers are broken down into amino acids.
• Fat polymers are broken down into glycerol and fatty acids (FFA).

Amino Acids

• Amino acids have an amino group and a carboxyl group attached to the same carbon atom, called the α-carbon.
• The R-group (side chain) determines the chemical properties of amino acids.
• GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter. It is notable because its -NH2 group is bonded to the carbon atom three carbons away from the carboxyl one.

Peptides

• Peptides are chains of amino acids.
• Dipeptides have 2, Tripeptides have 3, Oligopeptides have 4-20, and Polypeptides have over 20 amino acids.
• Peptides are read from the N-terminus to the C-terminus.
• Peptide bonds form between the carboxyl group of one amino acid and the amino group of another, releasing a water molecule (dehydration reaction).

Peptide Bond Formation

• A peptide bond is also an amide bond.
• It is a special type of covalent bond due to resonance.
• There is no free rotation around the peptide bond.
• The peptide bond is planar.

Hydrolytic Enzymes

• Hydrolytic enzymes break the peptide bonds to break down peptides into smaller fragments or individual amino acids.
• Examples of hydrolytic enzymes are trypsin and chymotrypsin. Trypsin cleaves the -COOH end of arginine, lysine, phenylalanine, tyrosine, and tryptophan. Chymotrypsin cleaves the -COOH end of aromatic amino acids.

Peptide Types by Number

• Dipeptide = 2 amino acids, 1 peptide bond
• Tripeptide = 3 amino acids, 2 peptide bonds
• Oligopeptide = a few amino acids
• Polypeptide = many amino acids (<10 kDa)
• Protein = thousands of amino acids (>10 kDa)

Characteristics of the Peptide Bond

•  Partial double bond character in peptide bonds restricts rotation.
• The six atoms (Cα,C,O,N,H, and Cα') are in a planar structure.

Biologically Important Peptides

• Dipeptides example: Aspartame
• Tripeptides example: Glutathione (GSH)
• Glutathione is a tripeptide of glutamate, cysteine, and glycine. It serves as a major redox buffer, a scavenger for oxidizing agents, is essential for maintaining red blood cell integrity and hemoglobin in ferrous state, and is involved in detoxification.
• Other peptides (e.g., angiotensin II, oxytocin, vasopressin) have roles in biological functions like blood pressure regulation, labor, and lactation.
• Toxic peptides (e.g., α-amanitin) can be lethal.