Topic 1.3:  Membrane Structure

Essential Idea:  The structure of biological membranes makes them fluid and dynamic.

At SHS, Topic 1.3 is taught in the following class unit(s):

• Cell Membrane Structure (unit 7)

Statements & Objectives:

1.3.U1  Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.

• Draw a simplified diagram of the structure of the phospholipid, including a phosphate-glycerol head and two fatty acid tails.
• Define hydrophilic and hydrophobic.
• Define amphipathic and outline the amphipathic properties of phospholipids.
• Explain why phospholipids form bilayers in water, with reference to hydrophilic phosphate heads and two hydrophobic hydrocarbon tails.​

1.3.U2  Membrane proteins are diverse in terms of structure, position in the membranes and function.

• State the primary function of the cell membrane.
• Contrast the structure of integral and peripheral proteins.
• List at least four functions (with example) of membrane bound proteins.
• Contrast the two types of transport proteins:  pumps and channels.​

1.3.U3  Cholesterol is a component of animal cell membranes.

• Identify the structure of cholesterol in molecular diagrams.
• Describe the structural placement of cholesterol within the cell membrane.​

1.3.A1  Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.

• Describe the function of cholesterol molecules in the cell membrane.​

1.3.S1  Drawing of the fluid mosaic model.

• Draw and label the structure of membranes.  Include:  
  • Phospholipid bilayer
  • Integral proteins shown spanning the membrane
  • Peripheral proteins on membrane surface
  • Protein channels with a pore
  • Glycoproteins with a carbohydrate side chain
  • Cholesterol between phospholipids in the hydrophobic region
  • An indication of thickness (10nm)​

1.3.S2  Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.

• Describe the observations and conclusions drawn by Davson and Danielli in discovering the structure of cell membranes.​

1.3.S3  Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model.

• Describe conclusions about cell membrane structure drawn from freeze-etched electron micrograph images of the cell membrane.
• Describe conclusions about cell membrane structure drawn from cell fusion experiments.
• Describe conclusions about cell membrane structure drawn from improvements in techniques for determining the structure of membrane proteins.
• Compare the Davson-Danielli model of membrane structure with the Singer-Nicolson model.​

1.3.NOS1  Using models as representations of the real world-there are alternative models of membrane structures.

• Explain what models are and their purposes in science.
• Describe the observations and conclusions drawn by Gorter and Grendel in discovering the structure of cell membranes.​

1.3.NOS2  Falsification of theories with one theory being superseded by another-evidence falsified the Davson-Danielli model.

• Describe why the understanding of cell membrane structure has changed over time.​

In the News:

• Development of a new imaging technique reveals complex protein movements in the cell membrane (2018-04-02)
• ​​Scientists create complex transmembrane proteins from scratch (2018-03-01)
• Receptors key to strong memories (2018-02-27)
• Living cell membranes can self-sort their components by 'demixing' (2017-12-05)
• Zooming-in on protein teamwork (2017-11-03)
• ​​​Biochemists devise snappy new technique for blueprinting cell membrane proteins (2015-06-05)