Globular and Fibrous Proteins Overview

Globular and Fibrous Proteins

• Globular proteins typically have a spherical shape due to tightly folded polypeptide chains.
• Hydrophobic amino acid groups are usually found on the inside of the protein, while hydrophilic groups are on the outside. This makes many globular proteins water-soluble.
• Examples include transport proteins (like hemoglobin and myoglobin), enzymes (like lipase and DNA polymerase), and hormones (like estrogen and insulin).
• Hemoglobin is a reddish-purple oxygen-carrying pigment found in red blood cells. It's made up of 4 polypeptide chains (2 alpha and 2 beta).
• The hydrophobic parts of the chains point inwards, while the hydrophilic parts point outwards. This helps maintain the protein's solubility in water.
• Hemoglobin contains a haem group with an iron ion (Fe2+) at its center.
• The iron combines with oxygen when oxygen concentration is high, releasing oxygen when oxygen concentration is low.
• One hemoglobin molecule can carry 4 oxygen molecules.
• The colour of hemoglobin is bright red when combined with oxygen, and purplish if not.

Fibrous Proteins

• Fibrous proteins generally have a long, narrow shape and are usually composed of long strands.
• They're primarily involved in providing structural support and strength.
• They often have little to no tertiary structure.
• Fibrous proteins usually have long parallel polypeptide chains, stabilized by cross-links that form fibers or sheets.
• Examples include collagen, keratin, and elastin.
• Collagen is a major structural protein found in connective tissues (such as skin, tendons, cartilage, bones, teeth, and walls of blood vessels).
• Collagen is a triple-helix made up of 3 polypeptide chains.
• Each chain consists of ~1000 amino acids.
• Every third amino acid in collagen is glycine to allow tight packing and forming a strong cable.
• Collagen has a repeating amino acid sequence, which makes it less sensitive to changes in pH or temperature, etc.
• Collagen molecules interact with each other to form fibers.
• Collagen has a high tensile strength, about one quarter that of mild steel.

Differences Between Fibrous and Globular Proteins

Feature: Fibrous ,Globular

Shape: Long and narrow ,Round or spherical

Purpose: Structural, Functional

Acid Sequence: Repetitive, Irregular

Durability: Less sensitive to changes in pH, temperature, etc. , More sensitive to changes in pH, temperature, etc.

Examples: Collagen, keratin, elastin Enzymes, hemoglobin, insulin

Solubility: Generally insoluble in water, Generally soluble in water

Incorrect Statement About Collagen

• Collagen has polypeptide chains primarily in an alpha-helix conformation. (This is false). Collagen has a triple-helix structure.

This quiz delves into the structure and function of globular and fibrous proteins, focusing on their unique shapes and roles in biological systems. Learn about important examples like hemoglobin, myoglobin, and key aspects of their solubility and interaction with oxygen. Test your knowledge on the characteristics that differentiate these protein types.