[Unit 4.1] | Structure Of The Cell Surface Membrane

Question 1

Name the 5 key components of the Fluid Mosaic Model (Plasma Membrane).

Answer 1

• Phospholipids
• Cholesterol
• Proteins (Intrinsic & Extrinsic)
• Glycolipids
• Glycoproteins

Question 2

Describe the features (2) and the functions (3) of a Phospholipid.

Answer 2

Features:
• Has a polar/hydrophillic head
• Has 2 non-polar/hydrophobic tails

Functions:
• Prevents water-soluble substances from passing across the membrane.
• Allows lipid-soluble substances to pass across the membrane
• Provides fluidity to the membrane.

Question 3

Define what an Extrinsic Protein is & describe its function.

Answer 3

• They do not span the length of the membrane.

• They provide structural support to the membrane.
• When paired with glycolipids, they function as cell receptors for molecules like hormones.

Question 4

Define what an Intrinsic Protein is & describe its function.

Answer 4

• A protein that completely spans the phospholipid bilayer.

• Channels: Water-filled tubes that allow water-soluble ions (charged particles) to cross the bilayer.
• Carriers: Bind to large molecules and change shape to transport the molecules across the membrane.

Question 5

What is the function of cholesterol within the bilayer?

Answer 5

• Decrease the fluidity of the membrane (by reducing the movement of phospholipids).
• They also play a role in preventing water loss from the cell (due to their highly hydrophobic nature).

Question 6

What does the prefix glyco- mean before lipid or protein?

Answer 6

It means that the lipid or protein is bonded to a carbohydrate molecule.

Question 7

What are the functions of glycolipids and glycoproteins?

Answer 7

• Act as cell recognition sites.
• Maintains membrane stability.
• Helps cells to join and form tissues.

• Glycoproteins do all of the above and also allow communication between cells.

Question 8

List 3 factors that prevent substances from being transported across the phospholipid bilayer.

Answer 8

• Insoluble in lipids
• Too large
• Polar / Charged

Question 9

Explain the meaning of “Fluid Mosaic” in relation to the phospholipid bilayer.

Answer 9

• Fluid: Individual phospholipids can move relative to one another so the membrane is flexible.
• Mosaic: The embedded proteins are arranged like tiles in a mosaic.