Unit 10: Membrane Structure

Question 1

what are the properties of membranes?

Answer 1

• grows with the cell
• deforms without tearing
• self healing

Question 2

are steroids found in prokaryote membranes?

Answer 2

nope just eukaryotes

Question 3

describe some of the fluidity within phospholipids in a membrane

Answer 3

molecules move constantly!

• change places w e/o
• rotate
• flip flop (top and bottom switch places, vv rare)

Question 4

how long can fatty acids be?

Answer 4

14-24 carbon atoms long

Question 5

describe the structure of membrane at higher temps.

Answer 5

longer fatty acids with less double bonds

Question 6

describe the structure of membrane at lower temps.

Answer 6

shorter fatty acids with more double bonds

Question 7

what do prokaryotes use to maintain fluidity?

Answer 7

just the change in structure based on temperature

Question 8

what type of organisms use cholesterol to modulate membrane fluidity?

Answer 8

eukaryotes

Question 9

how does cholesterol modulate membrane fluidity?

Answer 9

fills spaces between neighboring phospholipids, stiffening layer

Question 10

what percent weight does cholesterol makeup in plasma membrane?

Answer 10

20%

Question 11

what does fluidity in a membrane allow for?

Answer 11

proteins to diffuse rapidly and interact w e/o

Question 12

where does membrane assembly start?

Answer 12

in the ER

Question 13

what are phospholipids assembled by?

Answer 13

enzymes bound to the ER

Question 14

new phospholipids are inserted in the _____ side of the ER membrane

Answer 14

cytosolic

Question 15

what is the function of scramblase?

Answer 15

to basically randomly flip around phospholipids after they are inserted

Question 16

what is flippase? what is its function?

Answer 16

a family of enzymes found in the golgi that makes sure that specific phospholipids are in their right spot by flipping their position on the membrane.

uses energy frm ATP hydrolysis

Question 17

in a membrane, phospholipid distribution is ____

Answer 17

asymmetric

Question 18

glycolipids are located only on what side of the membrane?

Answer 18

non-cytosolic

Question 19

membrane _____ carry out most membrane functions

Answer 19

proteins

Question 20

membrane proteins make up what % of the plasma membrane mass?

Answer 20

50%

Question 21

what is the difference between integral and peripheral proteins?

Answer 21

integral - embedded in membrane
peripheral - js kinda sits on it

Question 22

what are some examples of integral membrane proteins?

Answer 22

• transporters and channels
• anchors
• receptors
  -enzymes

Question 23

what are transmembrane proteins?

Answer 23

amphipathic proteins that span the entire membrane.

Question 24

what are cytosolic proteins?

Answer 24

proteins that are attached to cytosolic side of membrane by amphipathic a-helix

Question 25

what are lipid linked proteins?

Answer 25

proteins attached to membrane via covalent bonds with lipids

Question 26

what are protein bound proteins?

Answer 26

proteins attached to membrane bc of interactions w other membrane proteins

Question 27

polypeptides cross the membrane as an _____

Answer 27

alpha helix

Question 28

single pass transmembrane proteins are often what?

Answer 28

signal receptors

Question 29

multi pass transmembrane proteins often form what?

Answer 29

series of amphipathic protein regions formed from a-helices that can eventually form aqueous pores

Question 30

what is a B-barrel?

Answer 30

cylindrical formation of rolled B-sheets with a hydrophilic inside channel and the outside being hydrophobic and in contact with fatty acid tails.

Question 31

where can B-barrels be found?

Answer 31

porin proteins!

Question 32

what is the function of porins?

Answer 32

are large, water filled pores in mitochondrial and bacterial membranes that allow for passage of small nutrients, metabolites and ions without letting big stuff through!

Question 33

why are membrane proteins difficult to work w?

Answer 33

they r amphipathic and since most tests happen in aqueous solutions, protein will fold up changing th structure and function of the protein

Question 34

how are membrane proteins then studied if cannot be in contact w water?

Answer 34

detergents solubilize the membrane, disrupting hydrophobic interactions and forming micelles. protein - detergent aggregates can be separated from lipid detergent aggregates.

Question 35

what do animal cells require since we dont have a cell wall?

Answer 35

cell cortex

Question 36

what is the cell cortex?

Answer 36

meshwork of filament proteins on underside (cytosolic side) of membrane, allowing the cell to selectively uptake materials, change shape and move

Question 37

what is spectrin?

Answer 37

a dimeric protein that makes up the cell cortex in red blood cells

Question 38

what are intracellular attachment proteins?

Answer 38

proteins that link spectrin to transmembrane proteins

Question 39

what are membrane domains?

Answer 39

functionally specialized regions in lipid bilayer where protein movement is restricted

Question 40

what are some examples of what membrane domains can do? give a specific example for each

Answer 40

- tether proteins to structures outside of cell (ec matrix, other cells) - tether proteins to structures inside cell (cell cortex) - restrict movement along tight junctions (ex. one side of epithelial cells in small intestine will absorb nutrients while other side will excrete those same nutrients)

Question 41

most membrane proteins are ____

Answer 41

glycoproteins!

Question 42

what are proteoglycans?

Answer 42

glycoproteins that contain one or more long polysaccharide chains

Question 43

what is the glycocalyx?

Answer 43

all carbs located on OUTSIDE of plasma membrane (therefore NOT on cytosolic side)

Question 44

what is the function of the glycocalyx?

Answer 44

acts as cushioning for membrane from mechanical stress

Question 45

what is the result of water molecules interacting with the glycocalyx?

Answer 45

slimy surface allowing for cell movement

Question 46

what is the structure of membrane carbs?

Answer 46

can be linear or branched but there is a huge variety of covalent linkages that can be made which allows for lots of diversity

Question 47

what is the function of membrane carbs?

Answer 47

- cell-cell recognition - adhesion