Membrane structure 1.3

The first models of membranes included protein and phospholipids but not in the same structure as we see them today. In this topic the components of cell membranes are investigated and the structure of the membranes as fluid and dynamic structures is outlined.


Key words

Learn and test your biological vocabulary for Membrane structure 1.3 using these flashards 

Clean sweep - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

Read the slides and look up any words or details you find difficult to understand.

Know the tricky details - for grade 7

These slides cover difficult parts of this topic - important if you are aiming for a high grade.
If grade 5 is your target, then save time, move on, study this information later, once you have revised the other topics.

Skills and applications

Explaining plasma membrane structure and the structure and function of the molecules in the membrane.

****  Video explainer here. ****

How to draw a diagram of a plasma membrane for an IB Biology exam  -  video tutorial

How to draw a membrane diagram in an exam from David Faure on Vimeo.

This explains how to draw a simple 2D diagram of a cell membrane, and label it for an IB Biology exam. It is worth practising how to do this before the exam.

Revision summary list for topic 1.3 Membrane structure

  • 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.
  • Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
  • Can you draw a diagram of the fluid mosaic model.
  • Can you explain how evidence from electron microscopy led to the proposal of the Davson-Danielli model.
  • Can you outline the evidence which led to the falsification of the Davson-Danielli model and support of the Singer-Nicolson model.

Revision pictogram / mindmap

This diagram summaries the main sections of topic 1.3 about membrane structure.
Test if you can draw your own list or concept map from memory.

Review questions

Multiple choice

This self marking multiple choice quiz contains questions covering the membrane structure.

1

Which property of phospholipid molecules describes the fact that they have both hydrophobic and hydrophilic parts?

Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules. The hydrophobic tails attract each other and the hydrophilic phosphates are attracted to the water.

Amphoteric substances may behave either as an acid or a base depending on the environment. Amino acids are said to be amphoteric because they both have a basic group (amine: NH2/NH3+) and an acid group (carboxylic acid) but this doesn't help them form bilayers.

2

Which of the following is true of peripheral proteins in cell membranes?

Membrane proteins are diverse in terms of structure, position in the membrane and function.
Peripheral proteins are attached to the membrane but found on its surface.

3

What effect does reducing the amount of cholesterol in a cell membrane have on its properties?

Cholesterol is a component of animal cell membranes. Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.

4

The photograph is from an electron microscope image of a membranes.
Parallel dark lines are clearly seen.
In electron micrography, heavy metal stains are often used to enhance contrast. DNA and Proteins often show as dark areas because these molecules can attach to the stain.

Which of the following interpretations is most similar to the proposal of the Daveson-Danielli model of membranes?


Students are expected to know how to use evidence from electron microscopy to support an idea about membranes. One illustration of this is the proposal of the Davson-Danielli model.

Further evidence lead to the falsification of the Davson-Danielli model and the proposal of the fluid mozaic model.

5

The illustration shown below is of a protein (green) attached to a membrane.

What is the most likely function of this membrane protein?

This protein is found in the human liver, where the hormone adrenaline indirectly stimulates it to mobilise stored energy inside liver cells in the "fight or flight" response.

The fact that it is a transmembrane protein is essential for this function.

It is interesting to note that this protein is also secreted by Anthrax bacteria as a toxin.
It upsets the metabolism of host cells when it enters them.

6

What is the name given to the type of molecule found in membranes which is made from carbohydrate and protein.

Glycoproteins have many functions in the human body, many involve interactions between cells.

Interestingly the hormones, FSH and LH are also glycoproteins.

Total Score:

Revision fun

If you can't see the content below, your browser is blocking the content. Please click this link to Membrane structure card match game

Alternatively this is a choice of Arcade games, which will help you to practise the basics while having fun.

If you can't see the content below, please click this link to the Classtools Arcade game "Membrane structure"