Cell Membrane

Question 1

Do Eukaryotic have membrane bound organelles?

Answer 1

Yes

Question 2

What are the 5 qualities of the cell membrane?

DCAMP

Answer 2

Delimits the cell
Functions in cell signalling 
Provides attachment sites
Controls movement of ions and molecules in and out of the cell
Protection from external environments

Question 3

What holds the lipid bilayer together?

Answer 3

non-covalent interactions

Question 4

What is embedded/attached in the lipid bilayer?

Answer 4

proteins

Question 5

What is the role of the proteins in the cell membrane?

Answer 5

Sense changes in the external environment and generates signals affecting cellular behaviour

Question 6

Which phospholipid is the only one with a negative charge?

Answer 6

Phosphatidylserine

Question 7

All phosphoglycerides are derived from what?

Answer 7

Glycerol with ethanolamine, serine, choline

Question 8

Sphingolipid called Sphingomyelin is derived from?

Answer 8

Sphingosine NOT CLYCEROL

Question 9

Phospholipids constitute how much of lipid mass in mammalian cell membrane ?

Answer 9

more than 50%

Question 10

Name an example of a glycolipid?

Answer 10

glycosphingolipid

Question 11

Lipid are s_____ and a______

Answer 11

Lipids are self organising and amphiphilic

Question 12

A small animal has how many lipid molecules organised in a bilayer?

Answer 12

10^9

Question 13

What do most cells stop excess lipids as?

How are adipocytes specialised?

Answer 13

Stored as lipid droplets/ a monolayer of phospholipids
neutral lipids ( hydrophobic bc no head)
with giant droplet filling cytoplasm

Question 14

How long are fatty acid tails?

Answer 14

14-24 Carbons in length

Question 15

What is the effect of cis-double bonds on the fatty acid tails and the bilayer overall?

Answer 15

Causes a kink

Greater number of double bonds the greater the kink and the more fluid the membrane

Question 16

What is the most common phospholipid in animal cells?

Answer 16

Phosphoglycerdies -3c backbone

Question 17

Describe the structure of a phospholipid

Answer 17

Amphiphilic molecule
Hydrophilic, polar choline, phosphate and glycerol head
Hydrophobic non polar fatty acid tail

Forms a self sealing sphere due to these properties

Question 18

How can artificial liposomes be created?

Answer 18

With phospholipids in aq sol.

Question 19

Describe the structure of cholesterol

Answer 19

Sterol
rigid ring structure
1 OH
short hydrocarbon chain

Question 20

How does cholesterol interact with membrane phospholipids

Answer 20

The polar hydroxyl head group inserts next to polar group in phospholipid

Question 21

Do plants have cholesterol?

Do bacteria have cholesterol?

Answer 21

Plants and bacterial cells do not have cholesterol

Plants have related sterol compounds instead

Question 22

When mixed with phospholipids what was the effect on cholesterol?

Answer 22

cholesterol mixed with phospholipids, decreases mobility of the bilayer/permeability to small H2O soluble molecules

Question 23

What is the effect of cholesterol on fluidity of the membrane at low temperatures

Answer 23

Cholesterol increases the spacing between the hydrocarbons

AND increased fluidity

Question 24

What is the effect of cholesterol on fluidity of the membrane at high temperatures

Answer 24

Cholesterol pulls the hydrocarbon tails together

AND decreases fluidity

Question 25

What is the effect of temperature on membrane fluidity ?

Answer 25

At low temp, fluidity decreases
reduced energy, phospholipids packed tighter together to produce a crystalline state

At a high temp, increasing fluidity
increased energy and pack less tightly

Question 26

What is flip flopping?

How else does the phosphoplid move?

Answer 26

Moving between planes is a rare occurrence with flexion (movement of hc tail) , rotation of the phospholipid.

It also moves rapidly laterally within the plane

Question 27

How do cis-double bonds affect membrane fluidity?

Answer 27

Cis-double bonds increases fluidity

bilayers are thinner, hc chains more spread out as chains more difficult to pack

Question 28

Proteins are mobile in the plasma membrane

Explain the experiment that showed this?

Answer 28

Human and mouse cells fused to form a hybrid cell,
Cell surface proteins monitored using antibodies with red and green florescent dyes
At time zero dyes, dye in either half of the Hybrid
After 40 min, dyes distributed over the entire cell surface.

Question 29

What is a lipid raft?

Answer 29

When plasma membrane segregates into specialised domains, domains enriched in cholesterol and sphingolipids form rafts that move laterally

Question 30

What are the suggested roles of lipid rafts?

Answer 30

cell signalling and uptake of extracellular molecules via endocytosis