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Cell Molec > Biomembrane Structure > Flashcards

Biomembrane Structure Flashcards

1
Q

Lumen

A

fluid filled interior of organelle

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2
Q

What is the bilayer membrane composed of

A

phospholipids

hydrophobic tails and hydrophilic heads

proteins embedded in

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3
Q

Fluid Mosaic model

A

individual phospholipids can move laterally and spin within the plane of the membrane – causing the fluidity

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4
Q

What give membrane strength

A

non-covalent interactions between phospholipids and between phospholipids and proteins

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5
Q

Hydrophobic core helps with what

A

prevents unassisted movements of water soluble substances from one side to the other

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6
Q

what do integral proteins often form

A

dimers and higher order oligomers

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7
Q

How do peripheral proteins associate with membrane

A

non-covalent interactions with integral proteins or membrane lipids

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8
Q

How are lipid anchored proteins tethered

A

covalently attached hydrocarbon chain

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9
Q

What is the core of the bilayer

A

extremely hydrophobic

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10
Q

Why is the hydrophobic bilayer a good thing

A

prevents diffusion of anything hydrophilic across the membrane and very stable interactions (hydrophobic-van der waals) hold together

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11
Q

How did some organelles obtain double membrane

A

endosymbiont hypothesis

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12
Q

Exoplasmic faces

A

outside of cell

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13
Q

Cystolic faces

A

facing the cystol of the cell

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14
Q

three classes of lipids in the biomembrane

A

Phosphoglycerides , sphingolipids, sterols

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15
Q

what is the most abundant lipid in the membrane

A

phosphoglycerides

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16
Q

Structure of phosphoglycerides

A

glycerol 3-phosphate bound to: 2 fatty acid chains (16 or 18 carbon long) and one of many different head groups

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17
Q

Different Head groups

A

choline head-> phosphatidylcholine
phosphatidylethanolamine
phosphatidylserine
phosphatidyl-inositol

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18
Q

Sphingolipids structure

A

sphingosine molecule ( amino alcohol with a long fatty acid tail) bound to a long fatty acid chain and one of several head groups

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19
Q

Sphingomyelin

A

phosphocholine head group and is important in nerve cells

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20
Q

Glycolipids

A

have sugar head group
usually on leaflet facing outside
helps protect cell
not a phospholipid

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21
Q

Structure of sterols

A

4 carbon rings w hydrophilic hydroxyl group on 1 ring

very hydrophobic

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22
Q

Do sterols form membranes

A

NO

they wedge themselves between other membrane lipids

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23
Q

Sterol function

A

to regulate membrane fluidity

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24
Q

Most abundant sterol in membrane?

A

cholesterol

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25
What contributes to fluid like consistency of the membrane
``` phospholipids can move laterally spin in place (like a top) vibrate flip sides of the bilayer ```
26
How are lateral movements of phospholipids detected
FRAP
27
FRAP process
1. label all molecules specific type membrane lipid with fluorescent dye 2. shine laser on small patch of membrane, bleaching dye in that area 3. measure how long takes labeled lipids to move into that spot (indicates rate of lateral movement
28
Factors Influencing membrane fluidity
1/ ratios of different types of lipids 2/ saturated v unsaturated phospholipids 3/ amount of cholesterol
29
Ratios of different types of lipids
some phospholipids make membrane more fluid | dif organelles have dif ratio of lipids
30
Saturated
all single bonds
31
unsaturated
at least one double bond
32
how does saturation affect membrane
``` saturated= membrane tends to be rigid unsaturated= membrane are much more fluid ```
33
Why does unsaturated fatty acid tails allow for more fluidity
put kinks in thus fatty acid tails cant pack as tightly
34
How does cholesterol affect fluidity of membrane
inserts itself between fatty acid tails of bilayer high concentration blocks phospholipids from moving laterally decreasing membrane fluidity low concentration prevents phospholipid tails from packing in tightly thus increasing membrane fluidity
35
Distribution of lipids in membrane
different leaflets of the bilayer have dif phospholipid compositions thus creating a difference in fluidity between two leaflets
36
why is a dif in fluidity between the two leaflets important
membrane curvature
37
lipid rafts
specific lipids grouped in patches in a single leaflet
38
properties of lipid rafts
rich in cholesterol resistant to detergent digestion rich in protein which usually function to transmit a signal from outside of the cell to the inside (hormone- receptor)
39
Which is thicker: sphingomyelin bilayer or phosphoglyceride?
sphingomyelin
40
Effect of cholesterol on phosphoglyceride bilayer vs the sphingomyelin
on PC increases thickeness but does not affect thickness of SM
41
Phospholipid shape of those with small head groups
conical
42
PC on the exoplasmic leaflet and PE on the cystolic face causes what
natural curvature
43
3 categories of membrane proteins
Integral, lipid anchored, peripheral proteins
44
How are integral proteins anchored
some to the cytoskeleton | some just more freely laterally
45
three domains of integral proteins
cytosolic, transmembrane, extracellular
46
What do each of the integral protein domains contain
extracellular contains one or more sugar attached (glycoproteins) Extracellular and cytoplasmic contain mostly hydrophilic amino acids transmembrane hydrophobic amino acids
47
Integral protein domains all consist of what
alpha helices or beta sheets
48
Lipid anchored proteins
covalently bonded to lipid tail, lipid embeds itself into 1 leaflet of bilayer
49
Peripheral membrane proteins
never interact with lipids, interacts with integral proteins or hydrophilic phospholipid head groups
50
3 added lipid groups on lipid anchored proteins
Fatty acyl group Prenyl group GPI anchor
51
What is a fatty acyl group
saturated fatty acid chain (14-16 carbons) | usually added to glycine or cysteine residue at beg or end of protein
52
What is a prenyl group
chain of prenyl units attached to cysteine residue
53
What is a GPI anchor
contains molecule of PI (two fatty acid tails are embedded in the membrane ), several sugar residues (outside of membrane), and ethanol amine (links to GPI anchor to the protein)
54
What moves slower lipids or proteins along the membrane
proteins (10-20 times slower)
55
Why do some membrane proteins not move
they have strong interactions with the cytoskeleton that underlies most membranes
56
How to measure movement of proteins along the membrane
FRAP and cell fusion assays
57
Cell fusion assays
1. fuse human and mouse cell 2. add mouse protein specific antibody, all the antibody label is 3. time for protein movement, mouse protein seen dispersed
58
Function of membrane proteins
``` receptors (EX. bind to hormones) enzymes cell adhesions proteins transport cell recognition ```
59
How are fatty acids synthesized
from acetyl CoA by water soluble enzymes and modified by elongation and desaturation in the ER
60
What facilitates movement of fatty acids
small cytosolic proteins
61
What moves phospholipids from one membrane leaflet to the opposite
flippases
62
How is cholesterol synthesized
enzymes in the cytosol and ER membrane
63
Fatty Acids are transported within cells by what
Fatty acid binding proteins
64
Step 1 of phospholipid synthesis in ER membrane
2 fatty acids from actyl CoA esterified to phosphorylated glycerol backbone forming phosphatidic acid whose two long hydrocarbon chains anchor molecule to membrane
65
Step 2 of phospholipid synthesis in ER membrane
phosphate converts phosphatidic acid into diacylglycerol
66
Step 3 of phospholipid synthesis in ER membrane
polar head group transferred from cytosine diphosphocholine to the exposed hydroxyl group
67
Step 4 of phospholipid synthesis in ER membrane
flippase proteins catalyze movement of phospholipids from the cytosolic leaflet in which that are initially formed to exoplasmic leaflet
68
Methods of cholesterol and phospholipid transport between membrane
A: vesicles transfer lipids between membranes B: lipid transfer is consequence of direct contact between membranes that is mediated by membrane embedded proteins C: transfer is mediated by small soluble lipid transfer proteins
69
synthesis of cholesterol
beta hydroxy beta methylglutaryl CoA converted to mevalonic acid by HMG-CoA Mevalonate then converted to isopentenyl pyrophosphate which can then be converted to cholesterol

Cell Molec (5 decks)

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