Lecuture 13 - Lipids and lipid membranes

Question 1

what er 2 functions of proteins along the cell membrane?

Answer 1

1. mediate the flow of nutrients and waste (transport)

2. relay information between the outside of the cell + the inside

Question 2

membrane proteins are either ______ the membrane

Answer 2

1. integral
2. linked to
3. peripheral

Question 3

what are membrane proteins characterized by?

Answer 3

-a hydrophobic protein-lipid interface

Question 4

transmembrane proteins are always _____

Answer 4

asymmetric

Question 5

what can integral membrane proteins contain?

Answer 5

• alpha helix bundles
• beta barrels
• bacteriorhodopsin
• porins in gram (-) bacteria

Question 6

what are 3 types of lipid linked membrane proteins?

Answer 6

1. GPI linked
2. prenylated
3. fatty-acid linked

Question 7

lipid molecules undergo _______ rapidly

Answer 7

lateral diffusion

Question 8

how do lipid molecules diffuse?

Answer 8

-along the bilayer

rapidly, minutes

Question 9

what type of diffusion is slow? (days)

Answer 9

transverse diffusion
(intrinsic flip flop rates)

Question 10

what kind of phospholipids are synthesized on the cytoplasmic side?

Answer 10

-PE

Question 11

what facilitates the transport of phospholipids synthesized on the cytoplasmic side?

Answer 11

-phospholipid translocase

EX: flippase, floppase, scrambase

Question 12

what is the fluid mosaic model of membranes?

Answer 12

-the membrane is viewed as a fluid background with domain that are pictured as either “islands” (fixed) or “icebergs” (floating)

Question 13

what are lipid rafts?

Answer 13

• membrane microdomains

- dissociate dynamically

Question 14

how are lipid rafts stabilized?

Answer 14

-by closely packed glycosphingolipids (GSL) and cholesterol

Question 15

what defines cell shape?

Answer 15

membrane skeleton

Question 16

what does the secretory pathway generate?

Answer 16

transmembrane and secreted proteins

Question 17

where are proteins synthesized?

Answer 17

ribosomes

Question 18

where are ribosomes?

Answer 18

-found in cytosol or bound to RER

Question 19

where are membrane proteins synthesized?

Answer 19

right on the ER membrane

Question 20

many proteins undergo further processing. How?

Answer 20

• pass through golgi apparatus before being
  1. integrated into cell membrane
  2. secreted to the EC space

Question 21

what initiates the secretory pathway?

Answer 21

1. signal protein

2. SRP and SRP receptor

Question 22

what are the 7 steps of the secretory pathway?

Answer 22

1.

Question 23

what completes the secreetory pathway?

Answer 23

vesicular transport

Question 24

what is vesicle budding and fusion aided by?

Answer 24

proteins

1. clathrin, COPI, COPII (budding
2. SNAREs (fusion)

Question 25

what is the benefit of using vesicles to transport proteins?

Answer 25

preserves their orientation relative to the membrane

Question 26

how are transmembrane proteins synthesized?

Answer 26

-on the ER membrane with its EC facing strand on lumen side

Question 27

which molecules can diffuse through the lipid membrane?

Answer 27

• lipids (steroids, fat soluble vitamins, fatty acids,

- small uncharged molecules (O2, CO2)

Question 28

what molecules do not pass through membrane freely?

Answer 28

-hydrophilic molecules
H2O
-Ions

Question 29

what are for types of transport?

Answer 29

1. carriers
2. passive transport (pores/channels)
3. active transport (proton pumps)
4. endocytosis/exocytosis

Question 30

what do cells actively maintain?

Answer 30

-concentration gradient between the cytosolic side and the extracellular space

Question 31

entropy has the tendency to ____ the concentration of everything

Answer 31

-homogenize