The fluid mosaic model of cell membranes

Question 1

What does it mean by the fluid mosaic model?

Answer 1

It means the molecules aren’t bonded together so there is movement but it is relatively stable due to the nature of the phospholipids.

Question 2

Why is the model fluid?

Answer 2

It is fluid because the individual phospholipid molecules can move within a layer relative to one another.

Question 3

Why is the model called a mosaic?

Answer 3

Is it called a mosaic as the proteins are embedded in the bilayer which can vary in shape, size and pattern.

Question 4

What is the bilayer?

Answer 4

It is when there are two layers of phospholipid molecules which are opposite one another.

Question 5

What is found in the inner layer and outer layer of phospholipids?

Answer 5

The inner layer of phospholipids has a hydrophilic head which point inwards towards the sale and interact with the water in the cytoplasm. The outer layer phospholipid has its hydrophilic head pointing outwards interacting with the water surrounding the cell.

Question 6

Where are the hydrophobic tails found?

Answer 6

The hydrophobic tails of the two layers point towards each other as they don’t interact with water. They point towards the centre of the membrane.

Question 7

What is able to pass through the phospholipid component of the membrane?

Answer 7

Lipid soluble molecules can cross the membrane however water-soluble molecules cannot.

Question 8

Where are extrinsic proteins found in the plasma membrane?

Answer 8

They are found on the exterior of the membrane where the extracellular size of the proteins are glycosylated to form glycocalyx.

Question 9

What is the function of extrinsic proteins?

Answer 9

They provide structural support and form recognition sites by identifying cells and the receptor sites for hormone attachment.

Question 10

Where are intrinsic proteins found in the plasma membrane?

Answer 10

They are located as part of the bilayer which extends across the layers. Transmembrane protein span the phospholipid bilayer where as others do not

Question 11

What are the functions of intrinsic proteins?

Answer 11

Some are carriers which transport water-soluble substances across and others allow active transport of ions across by forming channel proteins.

Question 12

Where is cholesterol found in the plasma membrane?

Answer 12

It is found between the fatty acid tails.

Question 13

Why is cholesterol important in the membrane?

Answer 13

As it provides the bilayer with stability and rigidity.

Question 14

What happens at low temperatures with cholesterol?

Answer 14

It increases the fluidity as the molecules are closely packed together.

Question 15

What happens at high temperatures with cholesterol?

Answer 15

Cholesterol decreases the fluidity so the molecules can move closer together.

Question 16

Protein + carbohydrate =

Answer 16

Glycoprotein

Question 17

Phospholipid + carbohydrate =

Answer 17

Glycolipid

Question 18

What is glycocalyx?

Answer 18

It is the carbohydrate layer around the membrane.

Question 19

What is the permeability of the membrane?

Answer 19

Lipid soluble substances and small molecules can dissolve within the phospholipid and simply to fuse across the membrane. As the phospholipid bilayer is hydrophobic lipid soluble molecules are freely permeable. Water soluble substances and polar molecules/ions can’t readily diffuse through the phospholipids this means that they must pass through intrinsic protein molecules which from water channels across the membrane. Resulting in the cell surface being selectively permeable to water and some solutes

Question 20

What happens when the temperature increases?

Answer 20

At low temperatures the molecules are packed closely together but when there is an increase in temperature and molecules found within the membrane gain more kinetic energy allowing them to move faster. This increases the fluidity of the membrane therefore permeable pigments and solutes are found in the innermost compartment.