Overview
This lecture introduces globular proteins, focusing on their structural features, water solubility, and how the structure of hemoglobin relates to its oxygen-carrying function.
Features of Globular Proteins
- Globular proteins have an approximately spherical shape.
- They are soluble in water due to hydrophilic (water-attracting) amino acids on their surface.
- Hydrophilic R groups interact with water molecules, allowing solubility.
- Hydrophobic (water-repelling) amino acids are buried in the center of the protein, away from water.
Types of Proteins
- Proteins are broadly divided into globular and fibrous types based on structure.
- This lecture focuses on globular proteins.
Structure and Function of Hemoglobin
- Hemoglobin is a globular protein found in red blood cells.
- It is composed of four polypeptide subunits: two alpha and two beta.
- Hemoglobin's function is to bind and transport oxygen in the blood.
- Each subunit contains a heme prosthetic group, making hemoglobin a conjugated protein.
- Each heme group contains an Fe²⁺ ion where oxygen binds.
- A single hemoglobin molecule can bind up to four oxygen molecules.
- Binding oxygen induces a change in hemoglobin’s quaternary structure, making it easier for additional oxygen to bind.
Key Terms & Definitions
- Globular protein — Protein with a compact, spherical shape, often soluble in water.
- Hydrophilic — Attracted to water; describes R groups that interact with water molecules.
- Hydrophobic — Repelled by water; describes R groups that avoid water.
- Prosthetic group — Non-protein component tightly attached to a protein (e.g., heme group).
- Conjugated protein — Protein containing a prosthetic group.
- Quaternary structure — Protein structure formed by multiple polypeptide subunits.
Action Items / Next Steps
- Review structures and functions of insulin and an enzyme in the next video.
- Be able to explain how the structure of each globular protein relates to its function.