5.1 The Structure And Function Of Membranes

Question 1

What is compartmentalisation?

Answer 1

Formation of separate membrane bound area in a cell

Question 2

Roles of the cell membrane

Answer 2

Function as a barrier between the cell and its environment - selectively permeable
Create concentration gradients
Cell membranes are required for cell signalling
Anchors the cytoskeleton
Endocytosis and exocytosis

Question 3

Plasma membrane

Answer 3

Cell surface membrane that separates the cell from its external environment

Question 4

Phospholipid bilayer

Answer 4

Hydrophilic phosphate heads of the phospholipids form the inner and outer surface of the membrane
The fatty acid tails of the phospholipids form a hydrophobic core

Question 5

Fluid mosaic model

Answer 5

Phospholipids are free to move within the layer (fluid)
This gives the membrane flexibility
Proteins embedded in the membrane vary in shape, size and position (mosaic)

Question 6

Intrinsic proteins

Answer 6

Embedded through both layers of a membrane

Amino acids with hydrophobic R groups on the external surfaces that interact with hydrophobic core

Question 7

Examples of intrinsic proteins

Answer 7

Channel proteins

Carrier proteins

Question 8

Channel proteins

Answer 8

Provide a hydrophilic channel that allows passive movement of polar molecules down a concentration gradient

Question 9

Carrier proteins

Answer 9

Important for both active and passive transport into cells

Involves the shape of the proteins changing

Question 10

Glycoproteins

Answer 10

Intrinsic proteins
Embedded in the cell surface membrane with attached carbohydrate chains
Part of cell adhesion
Receptors for chemical signals

Question 11

Cell signalling

Answer 11

When chemical binds to the receptor, it causes a response from the cell
This could cause a direct response or a cascade of events inside the cell

Question 12

Glycolipids

Answer 12

Intrinsic proteins
Lipids with attached carbohydrate chains
Cell markers/antigens and can be recognised as self or non self by the immune system

Question 13

Extrinsic proteins

Answer 13

Present in one side of the bilayer
Normally have hydrophilic R groups on outer surfaces and interact with polar heads of phospholipids
Can be present in either layer and some move between layers

Question 14

Cholesterol

Answer 14

Regulates fluidity of membranes
Cholesterol interacts with the hydrophobic phospholipid tails stabilising and causing packing together at higher temperatures