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Flashcards in chapter 10.1 (membrane structure) Deck (66):
1

What is the general rule when dealing with membrane proteins?

The metabolically active the more membrane proteins it contains

2

What is the protein composition of inner mito?

<75%
electron transport chain proteins
transport proteins
proteins that synthesize ATP

3

What is the protein composition of myelin sheaths?

<20%
serves as a insulator of nerve axon with lipids
myelin sheaths provide barrier for nerve axon

4

What are integral proteins?

all proteins that are fully or partially embedded in lipid bilayer

5

What are transmembrane proteins?

proteins that goes through the plasma membrane one or more times

6

What are the domains of transmembrane proteins?

membrane spanning
cytosolic
extracellular

7

What are various types of transmembrane proteins?

transporters/channels
receptors

8

What does the membrane spanning domains of transmembrane proteins usually contain?

helices that are 20-30 AAsand have hydrophobic R-groups

9

What does the lack of water within the bilayer promotes?

H-bonding between polypeptide backbone

10

What is a hydropathy plot?

allows for visualization of the hydrophobicity of a polypeptide that span the lipid bilayer.
assigns a positive number for the more hydrophobic R group
if a segment is more hydrophobic it shows up on the plot

11

What other forms may a membrane spanning protein form?

a membrane spanning structures formed from pleated sheets (beta barrels)

12

What is the length of the beta barrels?

~10 AA shorter than with helix
polypeptide crosses the membrane several times

13

how many strands are involved in forming the beta barrel?

8-22 strands

14

In which organisms are beta barrels usually found?

in bacteria membrane
outer membrane of mito/Chloroplast

15

What are monotopic integral proteins?

integral proteins that are only on side of a leaflet

16

What are the characteristics of a monotopic cystolic leaflet protein?

an amphipatic helix that has one hydrophobic surface within the cystolic leaflet. and one surface that interacts with the aqueous cytoplasm

17

What do monotopic cystolic leaflet proteins all have?

a significant hydrophobic surface and all are insoluble in aqueous solution

18

What are peripheral proteins?

- hydrophilic proteins associated with polar regions of other membrane proteins or the polar head groups of lipids. They are soluble in aqueous solution

19

What kind of bonds does peripheral proteins make with other membrane proteins?

association with membrane proteins usually by ionic and H-bonds (occasionally, disulfide bonds may be involved)

20

How can peripheral proteins be removed from the membrane?

removable from membrane w/ mild dissociation techniques b/c they are primarily hydrophilic and not hydrophobic

21

What are lipid linked proteins?

proteins are covalently attached to lipids within the bilayer

22

What are the different types of lipid anchors?

Fatty acid chain
prenyl group

23

What can a fatty acid chain do to a protein?

• single fatty acid chains can either stabilize a membrane spanning protein or be added after protein synthesis and attach a primarily soluble protein to the membrane

24

What is a GPI anchor?

made from a glycosylated PI phospholipid

25

When are GPI anchors added to a protein?

While the protein is being synthesized in the ER

26

What is the purpose of a GPI anchor?

links the protein to extracellular leaflet of the bilayer

27

How can lipid bilayer form?

form spontaneously from certain amphipathic lipids in aqueous solutions

28

What is the energy of bilayers?

the most stable (lowest free energy) association of phospholipids

29

What is the structure formed by lipid bilayers dependent on?

the type of phospholipid

30

What do bilayers and micelles do?

allow maximum contact of hydrophilic regions with H2O while shielding hydrophobic regions from H2O

31

What are micelles?

solid drops of lipid, formed from the aggregation of single fatty acids

32

What will groups of phosopholipids with two hydrocarbon tails will naturally form?

a bilayer in artificial or biological systems

33

What do lipid bilayers spontaneously form?

water filled spheres

34

What do phospholipid spheres minimize?

minimize free hydrophobic edge interactions w/ H2O and thus minimizes the free energy of the lipid/water interaction

35

What do the phospholipid bilayer allow?

sealing holes in membrane and membrane fusion.
implication for evolution of cell

36

What are liposomes?

artificially formed membrane spheres that are sometimes used to deliver large hydrophobic molecules into cells (eg, gene therapy, chemotherapy)

37

What are liposomes often used for?

a. often used in medicine to introduce polar compounds into cells

38

What are liposomes similar too?

b. essentially similar in structure to vesicles found in cells (without the usual proteins)

39

How do the lipid molecules interact with one another?

None of the lipid molecules in a membrane are covalently bound to each other
Lipids interact purely by hydrophobic interactions; thus all the lipid molecules are free to move within the bilayer

40

How doe the lipid bilayer move?

The bilayer acts as a 2-D fluid (restricted to lateral movement in x and y planes, not out of membrane, in the z-plane)

41

What are the movements of the lipid bilayer?

lateral
flip flop

42

What is the lateral movement of phospholipids?

movement of lipids within one plane of bilayer, within a leaflet/monolayer

43

What is the rate of lateral movement of a phospholipid?

rate of diffusion ~ 10-8 cm2/sec
a single lipid molecule can move completely around a bacterial cell in 1 sec

44

What is flip flop movement of lipids?

exchange between the two leaflets of a lipid bilayer

45

What is the rate of flip-flop movement of a lipid?

rare, slow (1 spontaneous, non-catalyzed event/day) due to polar head group having to move through lipid core

46

What are the evidence of membrane fluidity?

Cell fusion
FRAP = fluorescent recovery after photobleaching

47

What affects the how lipids and proteins move laterally within the bilayer and interact with one another?

fluidity of the membrane

48

What happens it the membrane is to rigid?

it takes too long for proteins to interact if necessary
some proteins have to diffuse along the bilayer to reach their target interaction

49

What happens if a membrane is too fluid?

membrane is leaky and an ineffective barrier

50

What is membrane fluidity dependent on?

temperature
types of fatty acids in phospholipids

51

What is the affect if the membrane is warm?

more fluid membrane (membrane melts)

52

What is the affect in colder membranes?

less fluid/more solid membrane (membrane freezes

53

What will be characteristic of artificial bilayers made from a single type of phospholipid?

melting and freezing points

54

What affect does phospholipids with shorter chain fatty acids have on fluidity?

more fluid (have lower melting points)

55

What affect does phospholipids with longer fatty acid chains have on fluidity?

less fluid (have higher melting points)

56

What affect does phospholipids with C=C bonds have on fluidity?

more fluid
cis double bonds forms a kink, prevents lipids from packing tightly together.

57

What type of tails does phospholipids usually have?

usually one unsaturated tail and one saturated tail

58

What is the response to temperature change in membrane proportional too?

the various type of lipids within that membrane

59

What is the role of cholesterol in animal cell membranes?

Due to its (weak) amphipathicity, cholesterol fits into bilayer in specific manner
Helps “plug gaps” between phospholipids, making membrane more stiff (similar to decreasing fluidity) and less permeable to water and small molecules

60

What do cells want to do with membrane fluidity?

keep it relatively constant to maintain proper function

61

what is proper fluidity is essential for?

mobility (function) of specific integral proteins and lipids

62

What is homeviscous adaptation?

the ability of species to modify the viscosity of lipids

63

What is the range that species keep the bilayer fluid at their body temperature?

3.2-3.5

64

What are poikilothermic organisms?

organisms who body temperature fluctuate wit the environment

65

Why is regulating bilayer fluidity important to poikilothermic organisms?

because their body temperature is dependent on the environment, if fluidity gets too fluid or rigid it will interrupt the normal function of the cell

66

How do poikilothermic organisms maintain a certain fluidity?

phospholipid content
• longer fatty acid chains = less fluid at physiological temps
• need higher temperature before the membrane “melts” (= become fluid)ii

proportion of saturated to unsaturated fatty acids (C=C bonds)
• the greater the saturation, more packed and less fluid the membrane at physiological temperatures
• with more C=C bonds, kinks in fatty acid chains keep molecules separated, so they can’t pack as tight (which makes them more fluid at physiological temperatures)

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