Membrane Structure

Question 1

Who invented the Fluid Mosaic model?

(1)

Answer 1

Singel and Nicolson (1972)

“Singer-Nicolson model”

Question 2

Explain the Fluid Mosaic model elements

(2)

Answer 2

1. Phospholipid bilayer
2. Integral and peripheral proteins

Question 3

What are the two kinds of proteins in the Fluid Mosaic model?

Clue: what does a mosaic consist of?

(2)

Answer 3

1. Integral proteins embedded in the phospholipid bilayer (i.e channels)
2. Peripheral proteins attached to the surface like the tiles of the mosaic (i.e globular structures)

Question 4

Where is the phospholipid bilayer present?

(1)

Answer 4

In all cellular membranes

Question 5

Why “Fluid” Mosaic Model?

(1)

Answer 5

Because the entire membrane is fluid

lipid molecules move within layers, floating proteins move freely

Question 6

Components of the phospholipid bilayer

(3)

Answer 6

1. Amphipathic phospholipids
2. Hydrophilic phosphate head
3. Hydrophobic hydrocarbon tail

Amphipathic: both hydrophobic and hydrophilic properties

Question 7

What happens when phospholipids are mixed with water?

What happens when a drop of oil goes under water?

Answer 7

Phospholipids spontaneously arrange with: hydrophilic heads outwards in contact with water and hydrophobic tails inwards towards eachother

Question 8

Structures and their functions in PB

(3)

Answer 8

1. Acts as barrier: controls E+E of ions and hydrophilic substances
2. Moving phospholipids: give fluidity so membrane can change shape and so endo-exocytosis can occur
3. Different lengths and saturations of fatty acids: controls fluidity

Question 9

What is exocytosis and endocytosis?

**Clue: absorbs and expels

(2)

Answer 9

Endocytosis: a process by which cells absorb external material by engulfing it with the cell membrane
Exotcytosis: a process by which a cell expels internal material by use of vesicles

Question 10

Which substances can cross the cell plasma membrane?

(2)

Answer 10

1. Non polar/hydrophobic molecules (i.e. O2)
2. Small hydrophilic molecules (i.e. H2O with use of channels)

Question 11

What is cholesterol?

(2)

Answer 11

1. A steroid present in animal cell membranes
2. Positioned between phospholipids

Question 12

What is the function of cholesterol in the cell membrane?

(3)

Answer 12

1. Reduces membrane fluidity
2. Reduces permeability to some small hydrophilic solutes (i.e. Na+)
3. Helps membrane curve in concave shape during endocytosis or vesicle formation

Question 13

What are integral proteins?

(3)

Answer 13

1. At least partly hydrophobic
2. Embedded in bilayer
3. Many are transmembrane, so amphipathic

Question 14

What are peripheral proteins?

(3)

Answer 14

1. Hydrophilic
2. Attached to surface of integral proteins
3. …Or anchored to membrane surface by hydrocarbon chain

Question 15

Protein to lipid ratio(s)

Clue: organelles

(3)

Answer 15

1. Protein to lipid is usually 50/50
2. In membranes active in respiration and photosynthesis (i.e. mitochondria or chloroplast) Protein to lipid is 75/25
3. In neurons protein to lipid is 18/82