Membrane Structure

Question 1

Of the other macromolecules, are lipids larger or smaller?

Answer 1

Smaller.

Question 2

Are membranes composed of just lipids?

Answer 2

NO, proteins AND lipids

Question 3

What does amphiphatic mean?

Answer 3

It means it has a hydrophilic and hydrophobic end.

Question 4

Are all membrane lipids amphiphatic?

Answer 4

YES

Question 5

What is the major component of membranes?

Answer 5

Phospholipids… more specificalls phosphoglycerides.

Question 6

What are some examples of hydrophilic head groups?

Answer 6

serine (AA), inositol (sugar), choline

Question 7

What is the difference between glycerides & galactides and sphingolipids?

Answer 7

Their backbones. glycerides and galactolipids have glycerol as their backbone while sphingolipids have sphingosine.

Question 8

What class are the greatest number of lipids? What is their general function?

Answer 8

Sphingolipids, they function as cell signals.

Question 9

Are triglycerols amphiphatic?

Answer 9

NO they are NOT. Since their head is also a fatty acid (hydrophobic) the entire molecule is hydrpophobic.

Question 10

Where are galactolipids commonly found?

Answer 10

Plant membranes

Question 11

Do glycolipids and phosphoilipids have a type with a sphingo or glycerol backbone?

Answer 11

YES

Question 12

How and where are fatty acids synthesizes?

Answer 12

By fatty-acid synthase in the cytosol of the liver.

Question 13

How are triglycerols transported? Where from?

Answer 13

VLDL

from the liver through blood to other tissues

Question 14

Where are triglycerols stroed?

Answer 14

adipose tissue

Question 15

How are triglycerols broken down? what is the purpose of this?

Answer 15

By lipases

for energy or to use the fatty acids for membrane lipid synthesis

Question 16

Where in the cell are membrane lipids synthesized and how are they then transported?

Answer 16

Synthesized in the smooth ER

1 - trnasported via vesicles

2 - transported via carrier proteins

3 - membrane to membrane contact in the same cell

Question 17

Name the 3 ionic and 1 polar head group of phospholipids that we discussed in class.

Answer 17

Ionic: phophatidylcholine, phosphatidylserine, and phosphatidylethanolamine

polar: phosphatidylinositol

Question 18

Describe the differences between a saturated fatty acid and an unsaturated fatty acid.

Answer 18

Saturated - saturated with H, no double bond, linear tail

Unsaturated - not saturated with H, contain a double bond. If cis then they have a kink but if they are trans they are not kinked.

Question 19

What is a liposome?

Answer 19

This is when PLs where observed in vitro to form spheres.

Question 20

Are phosphoglycerides mobile as a part of the membrane?

Answer 20

YES, the can move around to fill in tears and gaps in the membrane.

Question 21

What are some dietary examples of unsaturated and saturated fats?

Answer 21

cis unsaturated: vegetable oils (liquid at room temp)

trans unsaturated - hydrogenated vegetable oils (solid)

Saturated: Butter (solid at room temp)

Question 22

What do cholesterols do for the cell membrane?

Answer 22

They can be inserted into the membrane to stiffen it, filling the gaps formed by unsaturated tails.

Question 23

Which is more fluid, saturated or unsaturated?

Answer 23

Unsaturated

Question 24

What is Describe the role of scramblase and flippase.

Answer 24

Scramblase - when new phospholipids are formed in smooth ER, this enzyme catalyzes the transfer of random PLs from one monolayer to another.

Flippase - When new membrane lipids arrive from ER to the golgi flippase helps in transferring SPECIFIC PLs to the CYTOSOLIC monolayer of the new membrane, this is also present in the plasma membrane.

Question 25

Are PLs evenly distributed in the ER? What about the golgi, PM, and other compartments?

Answer 25

YES and NO

Question 26

What is the purpose of adding sugars to the glycolipids of the lumen of the golgi? Is this process reversible?

Answer 26

This prevents them from being flipped, ensuring that they remain on the outside surface of the cell, coating and protecting the cell. This process is reversible, can be glyosylated.

Question 27

Can changes in one phospholipids composition, including asymmetry of one cell, have an effect on another neighboring cell?

Answer 27

YES

Question 28

What molecules pass through the bilayer more easily? Which ones dont?

Answer 28

Easily: small molecules, nonpolar molecules Less easily: larger. charged or polar

Question 29

What is the main function of the bilayer?

Answer 29

to be selectively permeable by allowing only specific charged or large molecules to pass through it.

Question 30

What are four different ways that proteins associate with membranes?

Answer 30

Transmembrane - implanted throughout the entire bilayer. Monolayer - implanted in one of the layers Lipid-linked - linked to a lipid head Protein attached - linked to a membrane implanted protein

Question 31

What are 4 different functions of membrane proteins we discussed in class?

Answer 31

1. Transporters and channels 2. Anchors 3. Receptors 4. Enzymes

Question 32

Are the proteins and lipids of the membrane fluid or static?

Answer 32

fluid, can diffuse in any direction of plane of membrane

Question 33

Can the thickness of the bilayer of a cell vary?

Answer 33

YES

Question 34

What is a lipid raft?

Answer 34

These are protein-PL-cholestrol interactions that form a cluster.

Question 35

Describe the fluidity experiment and what it showed about PLs.

Answer 35

This is where two cells with two different labeled and dyed membrane proteins were fused, after being fused the labels appeared to be randomly dispersed throughout the hybrid cell from where they initially fused.

Question 36

What are some things that may limit the mobility of membrane proteins?

Answer 36

1. tethered to the cytoskeleton 2. tethered to the ECM 3. tethered to proteins of another cell 4. Diffusion barriers present on membrane limit mobility. LIKE TIGHT JUNCTIONS

Question 37

How can fluorescence recovery after photobleaching (FRAP) help to measure mobility of membrane proteins?

Answer 37

First you fluorescently label the membrane proteins, then you bleachan area with a laser, after this is done the unbleached proteins will move into the area of the bleaching, eventually the area will be filled in with new unbleched proteins completely making it hard to even tell the area was bleaching.