Lecture on Amino Acids and Zwitter Ions

Introduction

• Amino acids are organic compounds crucial in forming proteins.
• Video covers:
  • What amino acids are
  • Their acidic and basic properties
  • Formation of zwitter ions
  • Optical activity

Essential Concepts

• Amines:
  • Organic compounds derived from ammonia (NH3).
  • Contain nitrogen with a lone pair acting as a base (accepts H⁺ ions).
• Carboxylic Acids:
  • Contain a carbonyl group (C=O) and a hydroxyl group (OH) on the same carbon.
  • Act as weak acids, partially dissociating to form carboxylate ions.
• pH:
  • Scale for concentration of H⁺ ions.
  • Below 7 = acidic, above 7 = alkaline.
• Acids and Bases (Bronsted-Lowry definition):
  • Acids are proton donors, bases are proton acceptors.

Amino Acids Structure

• Have an amine (NH2) group and a carboxylic acid (COOH) group.
• Differ by the "R Group" attached to the central (alpha) carbon.
• Simplest amino acid: Glycine (R Group = Hydrogen).
• Undergo condensation reactions to form:
  • Dipeptides (two amino acids).
  • Polypeptides (long chains, forming proteins).

Zwitter Ions

• Definition: Compounds with full negative and positive charges, but no overall charge.
• Formation:
  • Internal acid-base reaction in amino acids.
  • Carboxylic acid group loses H⁺, forming carboxylate ion (negative charge).
  • Amine group accepts H⁺, forming ammonium ion (positive charge).
  • Charges cancel out, forming a zwitter ion.

Behavior in Solutions

• Neutral Solution:
  • Amino acids exist as zwitter ions.
• Alkaline Solution:
  • NH3⁺ loses H⁺ to OH⁻, forms NH2 (neutral).
  • Results in a negatively charged molecule.
• Acidic Solution:
  • COO⁻ accepts H⁺, reforming COOH (neutral).
  • Results in a positively charged molecule.

Isoelectronic Point

• pH at which an amino acid forms a zwitter ion.
• Varies among amino acids based on the R Group.
• Factors:
  • Acid strength and basicity influence the pH at which a zwitter ion forms.

Optical Activity

• Amino acids (except Glycine) have a chiral center (alpha carbon with four different groups).
• Can exist as optical isomers (enantiomers).
• Rotate plane-polarized light in opposite directions.

Conclusion

• Amino acids are vital for protein formation, displaying unique properties in different pH environments.
• Zwitter ions are central to understanding amino acid behavior.
• Isoelectric point and optical activity are key characteristics.

For further details, check related videos and resources available at chemistrystudent.com.