Cell Membranes & Membrane Proteins Flashcards
1
Q
what are cell membranes composed of
A
- phospholipid bilayer
- other lipids
- embedded proteins
- associated carbohydrates
2
Q
what is the role of the lipid sheets in cell membranes
A
- prevents molecules on one side from freely mixing w the other
- acts as selective barriers
3
Q
how do cell membranes act as selective barriers
A
- keep cell components separate form the environment
- compartmentalize intracellular space and enclose reactions
4
Q
what vital functions are cell membranes involved in
A
- communication w the environment
- import and export of materials
- flexibility for growth and movement
5
Q
the membrane surrounding a cell is referred to as what
A
the plasma membrane
6
Q
internal membranes within a cell form specialized compartments called what
A
organelles
7
Q
is the phospholipid bilayer thin or thick
A
- thin
- ~5nm
8
Q
what is the primary molecule in cell membranes
A
phospholipids
9
Q
describe the structure of phospholipids
A
- polar hydrophilic head
- 2 nonpolar hydrophobic hydrocarbon tails
- a molecule of glycerol
10
Q
what key characteristic of phospholipids is allowed by its structure
A
amphipathic characteristic
11
Q
what is the most common phospholipid in membranes
A
phosphatidylcholine
12
Q
describe the tail of phospholipids
A
- fatty acid
- hydrocarbon chain with a carboxyl group at one end
- can be saturated or unsaturated
13
Q
what happens if there is a double bond in one of the hydrophobic tails
A
makes it unsaturated
14
Q
what does phosphatidyl refer to
A
the phosphate-glycerol-fatty acid portion of the molecule
15
Q
describe the specific structure of phosphatidylcholine
A
16
Q
how do membrane components form a relatively stable membrane
A
- amphipathic nature which forms the bilayer
17
Q
what happens to amphipathic phospholipids in water
A
form a bilayer
18
Q
describe the relationship between amphipathic molecules and their exposed edges
A
- exposed edges are energetically unfavourable
- so they assemble into self-sealing containers without exposed edges (like a sphere)
19
Q
what is formed when pure phospholipids are added to an aqueous environment
A
small spherical liposomes
20
Q
what structures are studied to understand cell membranes and applications
A
small spherical liposomes
21
Q
what were used to deliver mRNA COVID vaccines
A
lipid nanoparticles (similar to liposomes but with more complex structure)
22
Q
how does the lipid bilayer behave
A
like a 2D fluid
23
Q
how does a lipid bilayer behave as a 2D fluid
A
- phospholipids are flexible
- can move// change position relative to one another
- spontaneous movement form one layer to another is rare
24
Q
what influences cell membrane fluidity
A
- density
- hydrocarbon tail length (14-24 C atoms)
- presence and number of double bonds (saturated vs unsaturated)
25
what does the fluid mosaic model show
other components of the membrane can diffuse laterally through the fluid lipid phase
26
what role does cholesterol play in membranes
- inserted among phospholipids to help stiffen and stabilize the membrane
27
what are the benefits related to cholesterol integration into cell membranes
- selective
- permeable
- strength
- stability
28
are membranes symmetrical
no (different phospholipids are found on the inside and outside layers of the membrane)
29
where is phosphatidycholine primarily found
non-cytosolic layer
30
where is sphingomyelin primarily found
non-cytosolic layer
31
where is phosphatidylserine primarily found
cytosolic layer
32
where is phosphatidylethanolamine primarily found
cytosolic layer
33
where is phosphatidylinositol primarily found
concentrated in cytosolic layer
34
where is glycolipids primarily found
exclusively in non-cytosolic layer
35
where does membrane assembly begin
in the endoplasmic reticulum
36
how are new phospholipids added to the bilayer
- enzymes associated w the cytosolic surface of the ER use free fatty acids
- they are added exclusively to the cytosolic half of the bilayer
- scramblase transfers random phospholipids from one monolayer to another
37
is all of the newly formed membrane distributed throughout the cell
- no
- some remains in the ER
38
where can additional asymmetrical modifications be made to the membrane
golgi apparatus
39
how does the golgi apparatus make modifications
- uses flippase to catalyze the transfer of specific phospholipids to cytosolic monolayer
- maintains membrane characteristics in animal cells
40
what is flippases
phospholipid-handling transporter found in the golgi apparatus membrane
41
how is asymmetry in membranes maintained
by moving by a provess of budding and fusing
42
what is the role of lipid rafts
concentrated sites of signaling and receptor molecules
43
what is different about the structure of raft regions in a membrane
- higher proportion of cholesterol and sphingolipids
44
where are lipid rafts found
small portions of the non-cystolic layer of the membrane
45
how much of animal cell membranes' mass are made up of proteins
~ 50%
46
what are some different kinds of membrane proteins
- transporters
- ion channels
- anchors
- receptors
- enzymes
47
what are transmembrane proteins
- extend through the bilayer
- part of their mass on either side
- amphipathic (both hydrophobic and hydrophillic regions)
- hyrdophobic regions are inside the bilayer, hydrophillic are exposed to the aqueous regions on either end
48
what are monolayer-associated proteins
- located almost completely in the cytosol
- associated with the cytosolic half of the lipid bilayer
49
what are lipid-linked proteins
- lie entirely outside the bilayer (on one side or another)
- attached to the membrane by a lipid group
50
what are protein-attached proteins
- bound indirectly to one face of the membrane or the other
- held in place by other membrane proteins
51
describe the backbone of a polypeptide chain
- hydrophilic
- forms alpha helices
52
what determines the function of integral proteins
protein structure
53
how many times do integreal proteins cross the bilayer
- many cross once
- some are comprised by a series of helices that cross the bilayer several time
54
can integral proteins form beta sheets
- sometimes, but less common
- forms large aqueous pores
55
when do integral proteins form beta sheet
- in some bacteria and mitochondria
- to allow passage of small nutrients, metabolites, and ions, but not large molecules
56
do we know the complete structure of most membrane proteins
- nope
- relatively few are known
57
why don't we know the complete structure of many membrane proteins
they're difficult to isolate and study
58
what are some recent advances for investigation of membrane proteins
- x ray crystallography
- cyro-electron microscopy
- modelling
59
membrane-associated proteins play a central role in what aspect of the cell
- shape and integrity
60
the flattened shape in RBC is maintained by what
- spectrin
- *a dimeric protein that forms a lattice*
61
how is the membrane stabilized in animal cells
by a meshwork of filamentous proteins called **cell cortex**
62
protein movement may be restricted by what
- attachment to the cortex
- attachment to molecules outside the cell
- cell junctions
- diffusion barriers
63
restrictions on protein movement have what function
can organize proteins and help carry out their function
64
what are glycoproteins
short chains of sugars
65
what are proteoglycans
long chains of sugars
66
what is attached to many membrane-associated proteins
- sugars covalently attached
67
what is a glycocalyx
- sugar coating on the outside of the plasma membrane
- forms a physical barrier for anything trying to get in the cell
68
what forms the glycocalyx
- glycolipids
- glycoproteins
- proteoglycans
- *located on the non-cytosolic side of the membrane*
69
what do surface carbohydrates do
- protect and lubricate the cells
- play a key role in cell-cell recognition and adhesion
70
what binds specific oligosaccharide side chains
transmembrane proteins called **lectins**
71
