Lecture Notes: Amino Acids and Biomolecules

Introduction to Biomolecules

• Types of biomolecules:
  • Proteins
  • Carbohydrates
  • Lipids
  • Nucleic acids
• Most biomolecules are polymers made of repeating units called monomers.
• Understanding the monomers and their combinations is essential to grasp complex bodily functions.

Amino Acids

• Definition: Amino acids are monomers that form proteins.
• Structure:
  • All amino acids have an amino group (NH2) on one end and a carboxyl group (COOH) on the other.
  • The central carbon is known as the alpha carbon and has a side chain, or R-group.
  • The R-group varies across different amino acids and determines the amino acid's properties.

Types of Amino Acids Based on R-Groups

• Simple R-groups:
  • Glycine: R-group is a hydrogen atom.
  • Alanine: R-group is a methyl group.
• Hydrophobic:
  • Example: Leucine (R-group is alkyl substituent).
• Aromatic:
  • Example: Phenylalanine.
• Basic:
  • Example: Lysine (R-group has lone electron pair on nitrogen).
• Acidic:
  • Example: Aspartic acid (R-group has carboxyl group).
• Nucleophilic:
  • Example: Serine (R-group has hydroxyl group).

Essential vs Non-Essential Amino Acids

• Essential Amino Acids: Cannot be synthesized by the body, must be obtained from the diet.
• Non-essential Amino Acids: Can be synthesized by the body.

Polymerization of Amino Acids

• Amino acids polymerize to form proteins.

Equilibria of Amino Acids in the Body

• Amino acids exist in different forms depending on the pH:
  • Cationic form: Dominant in acidic environments; amino group is protonated.
  • Zwitterionic form: Dominant around neutral pH; both positive and negative charges present.
  • Anionic form: Dominant in basic environments; carboxyl group is deprotonated.
• The state of protonation of side chains can also vary with pH.

Example: Alanine

• At physiological pH, alanine exists in the zwitterionic form.
• Participates in protein synthesis with the aid of other molecules.

Conclusion

• Understanding amino acids is foundational for studying proteins and biochemistry.
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