1.3 Membrane Structure
Essential idea: The structure of biological membranes makes them fluid and dynamic
Nature of science: Using models as representations of the real world—there are alternative
models of membrane structure.
Falsification of theories with one theory being superseded by another—evidence falsified the
Davson-Danielli model.
Understandings:
• 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 DavsonDanielli model.
• Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson
model.
Draw the cell membrane
Add labels to these diagrams:
1
Identify structures a - j
Watch this:http://www.youtube.com/watch?v=n8ZvK0r9HIY
Draw and label the cell membrane in the space below:
2
Properties of Phospholipids
Define these terms:
hydrophobic
hydrophilic
amphipathic
How do the properties of phospholipids help to maintain the structure of cell membranes?
Annotate the diagram to explain this.
3
Properties of Membrane Proteins
Explain the difference between integral and peripheral membrane proteins:
Complete the table:
Type of protein
Role
Answer this past paper question:
Which of the following is not a function performed by a membrane protein?
A.
Hormone binding sites
B.
Cell adhesion
C.
Enzyme synthesis
D.
Pumps for active transport
(Total 1 mark)
Models of Cell Membranes
What key events happened in each year and what did they tell us about cell membranes?
1895
4
1917
1925
1935
1972
This is an electron micrograph of a cell membrane.
How many membranes can you see in this image?
Label the following:
phospholipid heads,
phospholipid tails,
intermembrane space
Explain why this image initially appeared to support the Davson-Danielli model of the cell
membrane:
What later discovery cast doubt on this theory? Explain.
What further three pieces of evidence showed that the Davson-Dainelli model was not correct
and why?
5
Name the technique used to produce this image.
Explain how it works.
What evidence can be seen in the image which led to the proposal of the
Singer-Nicholson model?
True or false?
Davson-Danielli’s model proposed that a layer of globular proteins surrounded a lipid bilayer.
Electron micrographs show membranes as a lighter layer surrounded by two darker layers.
Freeze-fracturing was a technique that provided support for the Davson-Danielli model.
Gorter and Grendel proposed the fluid mosaic model in 1972.
The current model is called “fluid” because the components can move around within it.
Key Terms https://quizlet.com/12854976/membrane-structure-transport-functions-flash-cards/
Past Paper Question
(a) Draw a labelled diagram to show the structure of a membrane (5)
6
7