Membrane structure

Nature of science:

Using models as representations of the real world—there are alternative models of membrane structure. (1.11) Falsification of theories with one theory being superseded by another—evidence falsified the Davson-Danielli model. (1.9)

• Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
• Membrane proteins are diverse in terms of structure, position in the membrane and function.
• Cholesterol is a component of animal cell membranes.

Applications and skills:

• Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
• Skill: Drawing of the fluid mosaic model.
• Skill: Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.
• Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model.

Guidance:

• Amphipathic phospholipids have hydrophilic and hydrophobic properties.
• Drawings of the fluid mosaic model of membrane structure can be two dimensional rather than three dimensional. Individual phospholipid molecules should be shown using the symbol of a circle with two parallel lines attached. A range of membrane proteins should be shown including glycoproteins.

• The explanation of the structure of the plasma membrane has changed over the years as new evidence and ways of analysis have come to light. Under what circumstances is it important to learn about theories that were later discredited?

Utilization:

• Syllabus and cross-curricular links:
• Biology
• Topic 2.3 Carbohydrates and lipids
• Topic 2.6 Structure of DNA and RNA