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Biochemistry > [2] Class 2:membrane > Flashcards

[2] Class 2:membrane Flashcards

1
Q

Sheet like structures that form closed boundaries between different compartments:

A

Biological membranes

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2
Q

Biological membranes mainly consist of _____ and _____. ALso, _____ are linked to lipids and proteins.

A

Lipids,
Proteins,
Carbohydrates.

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3
Q

MEbranes have both a _____ and a ______ unit.

A

hydrophilic and hydrophobic

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4
Q

These are embedded in lipid bilayers and mediate distinct functions

A

Specific proteins.

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5
Q

Biological membranes form ________ assemblies.

A

Non-covalent

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6
Q

Biological membranes are symmetric or asymmetric?

A

Asymmetric

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7
Q

3 common features of biological membranes:

A

Asymmetric

Fluid structure: lipids and proteins can diffuse rapidly in the plane but not across the membrane.

Electrically polarized: (-) inside

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8
Q

Membranes are _________ b/c they contain a hydrophilic unit [polar head] and hydrophobic tail [straight or wavy lines]

A

Amphipathic

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9
Q

Why does oil form a monolayer when placed in water?

A

Polar heads are in contact w/ the water and the nonpolar hydrophobic lipid tails project into air

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10
Q

What is a consequence of the amphipathic nature of the membrane lipids?

A

Membrane formation

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11
Q

What are the 2 possible membrane formations of amphipathic membrane lipids?

A

Micelle

Lipid bilayer

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12
Q

THis is a limited structure

A

Micelle

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13
Q

This is favored structure for phospholipids and glycolipids:

10^6 nm =1mm

A

Lipid bilayer [bimolecular sheet]

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14
Q

Formation of lipid bilayers is a _______ process

A

Self-assembly

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15
Q

3 MAjor driving forces for the assembly of lipid bilayer [bimolecular sheet]:

A

Hydrophobic interactions- major force

Van der waals

Electrostatic and hydrogen-bonding

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16
Q

Attractive forces btw hydrocarbon tails

A

Van der waals

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17
Q

Attractions btw polar head groups and water molecules:

A

Electrostatic and hydrogen-bonding

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18
Q

What predominantly holds the lipid bilayer together?

A

Hydrophobic interactions

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19
Q

Hydrophobic interactions have 3 consequences of lipid bilayer formation:

A

Inherent tendency to be extensive

Tend to close on themselves leaving no edges exposed w/ hydrocarbon chains-forms compartments

Self-sealing- energetically favorable

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20
Q

Lipid bilayer low permeability for

A

Ions and most polar molecules

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21
Q

How difficult is it for water to traverse the membrane?

A

Easy- it is small, high [ ] and lack of a complete charge

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22
Q

Are all biological membranes asymmetric?

A

Yes

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23
Q

Is there even distribution of lipid molecules in lipid bilayers?

A

No, asymmetrically distributed.

Inner and outer leaf =different

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24
Q

Membrane ________ have unique orientations.

A

Proteins

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25
Q

Where is cholesterol present?

A

Large amounts of cholesterol are present in both leaflets- thought to be about equally distributed in both mono layers

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26
Q

Hydroxyl group of cholesterol is positioned wherein the membrane?

A

Near the polar heads of the phospholipid.

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27
Q

Rapid diffusion:

A

Lateral diffusion

-generally not stationary…fluid mosaic

28
Q

Very slow diffusion:

A

Tranverse or flip-flop diffusion…Req’s more energy

29
Q

Do proteins move in the fluid mosaic model?

What diffusion can they perform?

A

Yes, laterally they do not flip-flop or tranverse diffuse through membrane.

30
Q

How long does it take a phospholipid molecules to flip-flop?

A

Once in a several hours.

31
Q

During the tranverse and lateral diffusion, can asymmetry be preserved?

A

Yes

32
Q

Membrane fluidity is controlled by:

A

FA composition

And cholesterol content

33
Q

Fatty acid composition affects membrane fluidity how?

A

Length of FA chains;
Saturation levels;
Position of double bonds [cis]-provides more fluidity.

34
Q

How does cholesterol content affect membrane fluidity?

A

Bidirectional…stabilizes at high Temp. And more flexibility at low temps.

35
Q

Provides an environment where signal transduction and molecule transportation take place:

A

Cholesterol content

36
Q

How do you classify difference in membrane proteins?

A

Based on the difference in dissociability

37
Q

Interact extensively w/ hydrocarbon chains of membrane lipids.
Can be released ONLY by agents that compete for these nonpolar interaction-organic solvents and detergents.
Spans the entire lipid bilayer:

A

Integral membrane proteins

38
Q

What aspect of the bimolecular sheet [lipid bilayer-membrane] is responsible for most of the dynamic processes?

A

Membrane proteins

39
Q

How do different membranes differ?

A

Protein content

40
Q

HOw can one view proteins in a membrane?

A

Sodiumdodecylsulfate polydactyl amine gel electrophoresis (SDS/PAGE)

41
Q

A light-driven proton pump converts the energy of light into trans membrane proton gradient that is used to synthesize ATP:

A

Bacteriorhodopsin (BR)

42
Q

Bacteriorhodopsin is built almost entirely of ______ b/c most amino acids are nonpolar and arranged ________ to the bilayer plane.

A

Alpha helices

Perpendicularly

43
Q

The most common structure motif in membrane proteins:

A

Membrane-spanning alpha helices

44
Q

Ex of integral protein that binds to luminal leaflet of the ER.
It is a homodimer consisting of primarily Alpha helices.
It is NOT a membrane-spanning protein

A

Cyclooxygenase [COX] 1

ALso called
Prostaglandin H2 synthase [PGHS] 2

45
Q

These are bound to membranes primarily by electrostatic and hydrogen-bond interactions:

A

Peripheral membrane proteins

46
Q

Peripheral membrane proteins dissociate from membrane by adding:

A

Salt or pH changes

47
Q

Peripheral membrane proteins are bound to surfaces of:

A

Integral proteins bound on either:
Cytosolic or extracellular side of membrane
OR

Anchored to lipid bilayer by COVALENTLY attached hydrophobic chain; i.e. FA

48
Q

How are lipids asso. W/ proteins?

A

Covalently

49
Q

Lipids anchor their attached proteins to membrane and mediate protein-protein interactions.
3 kinds of modification:

A

Palmitoylation
Farnesylation
Glycosylphosphosphatidylinositol

50
Q

Modification Of cysteine residues by a thioester bond.

A

Palmitoylation

51
Q

Modification of cysteine residues at the C-terminus

A

Farnesylation

52
Q

modification link to the carboxyl terminus

A

Glycosylphosphatidylinositol

53
Q

Covalent attachment of a farnesyl (c15) unit to C-terminal tetrapeptide CAAX in which cys is followed by 2 aliphatic residues.
After farnesyl group is appended to protein in thioETHER linkage w/ cys residue, the AAX trip eptide is hydrolytic ally cleaved away.

A

Farnesylation at the C-terminus

54
Q

Functions of farnesylation at the C-terminus :

A

Anchoring the protein to the membrane and facilitating the protein-protein interaction.

55
Q

Thioester bond

A

Palmitoylation

56
Q

Thioether bond

A

Farnesylation

57
Q

Looks like O-glycosidic linkage:

A

GPI anchor

58
Q

GPI anchor:

A

Links proteins to OUTER leaflet

Many Cell-surface hydrolytic enzymes and adhesions are tethered by GPI unit

59
Q

Mitochondria 2 membrane systems:

A

Outer membrane and inner membrane

60
Q

Internal ridges and cristae

A

Inner membrane mito.

61
Q

2 compartments in mito.

A

Intermembrane space

Matrix

62
Q

Oxidative phosphorylation takes place in the:

A

Inner-mitochondrial membrane

63
Q

The site of most of the TCA cycle and FA oxidation:

A

Matrix

64
Q

This membrane is permeable to most small molecules and ions

A

Outer membrane

65
Q

Impermeable to nearly all ions and polar molecules:

A

Inner membrane

66
Q

VDAC

A

Mitochondrial porin

Biochemistry (13 decks)

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