Amino Acids, Proteins and DNA

• What two functional groups are present in amino acids?

  Amine and carboxylic acid
• In α-amino acids, the amine and carboxylic acid groups are attached to the same carbon.
• With the exception of glycine, naturally occurring amino acids contain a chiral carbon atom.
• Why are amino acids considered amphoteric?

  They react with both acids and bases
• The isoelectric point of an amino acid is the pH at which the molecule has no net electrical charge.
• At the isoelectric point, amino acids exist as dipolar ions or zwitterions.
• Match the amino acid R group with its isoelectric point:

  Glycine (-H) ↔️ 5.97

  Glutamic acid (-(CH2)2COOH) ↔️ 3.22

  Lysine (-(CH2)4NH2) ↔️ 9.59
• Amino acids are crystalline solids with relatively high melting points.
• In which type of solvent do amino acids dissolve well?

  Polar solvents
• A peptide is a compound made of amino acids joined by peptide links.
• What type of reaction forms peptide links between amino acids?

  Condensation
• Steps in the formation of a peptide link

  1️⃣ Water is removed

  2️⃣ Amino acids join together

  3️⃣ Amino acid residue is formed
• What type of charge does an amino acid have at a pH lower than its isoelectric point?

  Positive
• At a pH higher than its isoelectric point, an amino acid behaves as an acid.
• Polypeptides are condensation polymers of amino acids.
• Peptides can be hydrolysed in acidic or alkaline conditions.
• Hydrolysis is the breaking of a bond using water.
• Match the hydrolysis type with its reagents:

  Acid hydrolysis ↔️ 6 mol dm-3 HCl(aq)

  Alkaline hydrolysis ↔️ Moderately concentrated NaOH(aq)
• Steps in separating amino acids using thin layer chromatography (TLC)

  1️⃣ Prepare the TLC plate

  2️⃣ Apply the sample to the plate

  3️⃣ Run the chromatogram

  4️⃣ Develop the spots using ninhydrin
• Proteins are condensation polymers of amino acids joined by peptide links.
• The primary structure of a protein refers to the sequence of amino acid residues.
• Match the secondary structure with its description:

  α-helix ↔️ Spiral structure with R groups pointing outwards

  β-pleated sheet ↔️ Planar arrangement of polypeptide backbone
• What type of bonding holds the secondary structure of proteins together?

  Hydrogen bonding
• How many moles of water are produced when a tripeptide is formed from three amino acids?

  2 moles