LS4002 - Shapes of Biomolecules Lecture 8 - cis and trans isomers

Learning Outcomes

Key Concepts to Identify:

  • Cis and Trans Double Bonds: Understanding the geometric isomerism in alkenes, particularly how cis double bonds have substituents on the same side while trans double bonds have them on opposite sides.

  • Cis and Trans Groups on a Ring: Recognizing the arrangement of groups in cyclic structures and how it affects the physical and chemical properties of the compound.

  • Alpha and Beta Groups on a Sugar Ring: Identifying the anomeric carbon in sugars and how the orientation of hydroxyl groups defines the alpha or beta forms.

Biomolecules with Cis or Trans C=C Bonds

Cis-Polyisoprene

  • Source: Found naturally in the latex of the rubber tree (Hevea brasiliensis) in tropical regions, commonly known as India rubber.

  • Structure: Features chains of C=C double bonds where the substituents are on the same side, contributing to its properties.

  • Applications: Used in a variety of products including tires, footwear, and elastic materials due to its remarkable elasticity.

Trans-Polyisoprene

  • Source: Derived from the sap of the Palaquium gutta tree, commonly known as Gutta-Percha.

  • Structure: The double bonds are arranged with substituents on opposite sides, contributing to its rigidity.

  • Applications: Primarily used in dental applications for root canal fillings and other medical uses due to its strength and stability.

Physical Properties

  • India Rubber: When heated with sulfur, the process known as vulcanization induces the formation of cross-links between polymer chains, enhancing elasticity, durability, and resistance to degradation.

  • Gutta-Percha: Unlike India rubber, Gutta-Percha exhibits a more rigid structure, making it suitable for applications requiring stability and strength such as dental materials.

Terpenes and Isoprene Units

  • Polyisoprenes: These biopolymers are formed through the polymerization of 5-carbon isoprene units, showcasing a significant range of properties based on their structure and configuration.

  • Squalene: A naturally occurring compound, found in high concentrations in shark liver oil, represents a trans-alkene which serves as a precursor for essential biomolecules like cholesterol and steroid hormones. Additionally, it is present in olive oil and has been studied for its potential health benefits, including antioxidant properties.

Carotenoids

  • Beta-Carotene: This pigment is a crucial provitamin A, essential for vision and immune function due to its conversion to vitamin A in the body. It is found in high concentrations in carrots and other colorful fruits and vegetables.

  • Lycopene: Known for imparting a red color to tomatoes, lycopene is an all-trans isomer studied for its potential health benefits, including reducing the risk of certain cancers and promoting heart health.

  • Curcumin: Derived from turmeric, this compound is recognized for its anti-inflammatory and antioxidant properties. The presence of conjugated double bonds enhances its biological activity and contributes to its vivid yellow color.

Sugars - Isomers

  • Importance of Isomerism in Sugars: Sugars such as D-Glucose demonstrate the significance of spatial arrangement on biological function. They can exhibit cis and trans configurations, leading to different properties and reactions.

  • D-Glucose: This sugar exists in both cis (beta) and trans (alpha) forms based on the orientation of hydroxyl groups on the anomeric carbon. These forms have different physical properties and biological activities:

    • B-D-Glucose: In this configuration, the hydroxyl group on the first carbon is on the same side as the CH2OH group, representing the beta form.

    • a-D-Glucose: In contrast, this form has the hydroxyl group on the first carbon on the opposite side from the CH2OH group, defining the alpha form.

Understanding these molecular configurations and their implications is crucial in fields such as biochemistry, nutrition, and material science, influencing everything from drug design to the development of new materials.