Membrane Structure topic 1.3

Question 1

Phospholipid Bilayer

Answer 1

Phospholipid bilayers are critical components of cell membranes. The lipid bilayer acts as a barrier to the passage of molecules and ions into and out of the cell.

Question 2

Structure of Phospholipids

Answer 2

• Contain a polar (hydrophilic) head composed of phosphate (+ glycerol)
• Contain two non-polar (hydrophobic) tails, each composed of a fatty acid chain
• Hence, phospholipids are amphipathic (have hydrophilic and hydrophobic parts)

Question 3

Arrangement in Membranes

Answer 3

• Phospholipids spontaneously arrange into a bilayer
• The hydrophilic phosphate heads face out into the surrounding solution, while
  the hydrophobic fatty acid tails face inwards and are shielded from the polar fluids

Question 4

Properties of the Phospholipid Bilayer

Answer 4

• The bilayer is held together by weak hydrophobic interactions between the tails
• Individual phospholipids can move within the bilayer (fluidity and flexibility)
• Amphipathic properties restrict passage of certain substances (semi-permeable)

Question 5

Cholesterol

Answer 5

Cholesterol is a fundamental component of animal cell membranes
* It is not present in plant cell membranes (as they have a rigid cell wall)

Question 6

Functions of cholesterol

Answer 6

Cholesterol reduces membrane fluidity and permeability to some solutes
* It also anchors certain peripheral proteins and prevents crystallization

Question 7

Membrane proteins serve many functions: JETRAT

Answer 7

• Junctions
• Enzymes
• Transport
• Recognition
• Anchorage
• Transduction

Question 8

Cell membranes are represented as a fluid-mosaic model

Answer 8

• Fluid – membrane components can move position
• Mosaic – phospholipid bilayer is embedded with protein

Question 9

Membrane Models

Answer 9

Membranes appear trilaminar when viewed with an electron
microscope (trilaminar = three distinct layers)