Textbook 2.1

Question 1

plasma membrane

Answer 1

5 to 10 nm wide. Not detectable under a light microscope, only became detectable in 1950s with electron micrographs. Appearance of three layered structure (inner outer and middle layer) where the inner is the non polar region and outer two layers are the polar regions

Question 2

Which membranes show three layer structure?

Answer 2

All membranes; plasma, nuclear, or cytoplasm have this structure.

Question 3

Cell membrane functions

Answer 3

1. Compartmentalization - allows specialized activities to take place without external interference
2. Scaffold for biochemical activities - stuff in membranes is no longer floating around in solution; can be ordered for effective interaction
3. Providing a selectively permeable barrier
4. Transporting solutes (across membrane)
5. Responding to external stimuli (ligands, light, mechanical tension)
6. Intercellular interaction
7. Energy Transduction

Question 4

How is the membrane involved in responding to external stimuli and intercellular interaction?

Answer 4

• Membranes have different types of receptors that combine with ligands (molecules) or respond to light or mechanical tension.
• It mediates interactions between cells allowing them to signal and recognize each other, to adhere and to exchange materials and info.

Question 5

How did Gorter and Grendel propose presence of a lipid bilayer

Answer 5

Extracted lipids from mammalian red blood cells which do not have nuclei or organelles (so all lipids would be from plasma membrane) and calculated ratio of surface area of lipids over water (phospholipids form a one molecule thick layer spread over aqueous solution) to the surface area of red blood cell. SA ratio was 2:1 thus -> bilayer

Question 6

Why is surface tension lower in membranes than in pure lipid structures?

Answer 6

Presence of proteins

Question 7

Plasma membranes =

function of both components

Answer 7

lipid + proteins (noncovalent bonds)

• lipid is structural backbone
• proteins carry out most of specific functions

Question 8

Three types of membrane lipids

Answer 8

Phosphoglycerides, sphingolipids, cholesterol all of which are amphipathic