The fluid mosaic model of cell membranes COPY

Question 1

When was the fluid mosaic theory first proposed and by who

Answer 1

Singer and Nicholson 1972

Question 2

What is the fluid mosaic model?.

Answer 2

The fluid mosaic model describes the structure of the plasma membrane

As a mosaic of components

including phospholipids, cholesterol, proteins, and carbohydrates

that gives the membrane a fluid character.

Question 3

What is the structure of a fluid mosaic model

Answer 3

Question 4

Why is a cell membrane called fluid mosaic?

Answer 4

• The reason it is described as fluid is because
  
  • The individual phospholipid molecules can move within a layer, relative to one another
• The reasons it is described as mosaic is because
  
  • The extrinsic and intrinsic proteins embedded in the bilayer vary in shape, size and pattern

Question 5

What has the fluid misaic model for the cell surface membrane been described as

Answer 5

A see of protein icebergs floating in a sea of lipids

Question 6

What controls the level of fluidity

Answer 6

Fatty acids can be saturated or unsaturated

Phospholipids will therefore contain saturated or unsaturated fatty acid tails

The membrane is more fluid when there is

• a high level of saturated fatty acids,
• the fatty acids have shorter tails
• or when there is an increase in temperature

The greater the level of steroids in the cell membrane, the less fluid it is.

Cholesterol is a steroid found in animal cells but rarely in plant cells.

It can fit between the phospholipid molecules increasing rigidiy and stability of the membrane as a whole

Question 7

What types of substance are able to dissolve in the phospholipid membrane and diffuse accross

Answer 7

• Lipid soluable substances
• e.g. Vitamin
• e.g. Small molecules O₂ and CO₂

Question 8

What type of molecule is able to pass through the cell membrane

Answer 8

The membrane is hydrophobic which means lipid soluable molecules are able to pass the membrane more easily than water soluable substances

Question 9

What type of molecules are unable to pass through the phospholipid molecules

Answer 9

• Water soluable substances
  
  • e.g Glucose
  • e.g. Polar molecules
  • e.g. Ions

Question 10

How do these water soluable substances pass through the cell membrane

Answer 10

• They pass through intrinsic protein molecule which form water filled channels accross the membrane
• as a result, the cell surface membrance is slectively permeable to water and some solutes

Question 11

What does the term selectively permeable mean

Answer 11

The cell membrane is permeable to watermolecules and other small molecule but no large molecules

The cell membrane is therefore a selective barrier