Membrane Structure and transport

Membrane structure

Davson-Danielli model (a) Singer-Nicolson model (b)

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

• Amphipathic phospholipids have hydrophilic and hydrophobic properties.
• 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.

• 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.

Can you create a membrane, in the time frame allowed, that will work correctly ? Can you identify organelles with lightning speed?

Click below to show your skills!

Membrane Game!

Do you know your organelles?

Membrane transport

Na+ K+ pump

Application: Structure and function of sodium–potassium pumps for active
transport and potassium channels for facilitated diffusion in axons.

Passive transport

Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
• The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.

how vesicles move cargo

Osmosis

Application: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions.
(Practical 2)

Design your experiment!