Lecture 16 - Membrane Lipids 1

Question 1

Biological membranes form ________ (covalent/non-covalent) assemblies.

Answer 1

Non-covalents

Question 2

Name the common features of biological membranes

Answer 2

Asymmetric
Fluid Structure
Electrically Polarized
Hydrophilic and Hydrophobic units

Question 3

What does it mean for a lipid to be amphipathic?

Answer 3

The lipid contains both hydrophilic and hydrophobic units

Question 4

Describe how oil forms a monomolecular layer on the surface of water

Answer 4

Polar heads are in contact with water

Nonpolar hydrophobic lipid tails project into the air

Question 5

What is responsible for membrane formation?

Answer 5

The amphipathic nature of membrane lipids

Question 6

What are the two possible arrangements of lipids?

Answer 6

Micelle or Lipid Bilayer

Question 7

When is a micelle formed?

Answer 7

Formed when a variety of molecules including soaps and detergents are added to water
Temporary and Fragile
Examples: SI bile detergents and partially digested fats

Question 8

Why is a bimolecular sheet more favorable than a micelle?

Answer 8

Two fatty acyl chains of a phospholipid or a glycolipid are too bulky to fit into the interior of a micelle

Question 9

Why are phospholipids and related molecules important membrane constituents?

Answer 9

They readily form extensive bilayers

Question 10

Formation of lipid bilayers is a _________ (self or group- assembly) process

Answer 10

Self-assembly

Question 11

What are the major driving forces for the assembly of lipid bilayers?

Answer 11

Hydrophobic interactions
Van der Waals attractive forces between hydrocarbon tails
Electrostatic and hydrogen-bonding attractions between polar head groups and water molecules

Question 12

What are the three significant consequences of the hydrophobic interactions between lipids?

Answer 12

Bilayers have an inherent tendency to be extensive
Bilayers will tend to close on themselves so that there are no edges with exposed hydrocarbon chains, and so they form compartments
Bilayers are self-sealing

Question 13

Why are bilayers self-sealing?

Answer 13

The bilayer wants to be thermodynamically stable. A hole in the bilayer is energetically unfavorable

Question 14

Why is water able to traverse the membrane easily?

Answer 14

B/c of its small size, high concentration, and lack of complete charge

Question 15

The lipid bilayer has a low permeability for what?

Answer 15

ions and most polar molecules

Question 16

What are the two classifications of membrane proteins and what determines this classification?

Answer 16

Integral membrane proteins
Peripheral membrane proteins
Classified according to the difference in dissociability

Question 17

What do integral membrane proteins interact with?

Answer 17

Extensively with the hydrocarbon chains of membrane lipids

Question 18

How do you release integral membrane proteins?

Answer 18

Can be released by agents that compete for the nonpolar interactions, such as organic solvents and detergents

Question 19

What is responsible for most of the dynamic processes carried out by membranes?

Answer 19

Membrane proteins

Question 20

How can one visualize the protein components of a membrane?

Answer 20

SDS-polyacrylamide gel electrophoresis

Question 21

How are peripheral membrane proteins bound to the membrane?

Answer 21

By electrostatic and hydrogen-bond interactions with the head groups of lipids

Question 22

How do you remove peripheral proteins from the membrane?

Answer 22

Salt or pH changes

Question 23

Peripheral membrane proteins are bound to the surfaces of integral proteins either on:

Answer 23

the cytosolic or extracellular side of membrane or anchored to the lipid bilayer by a covalently attached hydrophobic chain, such as a fatty acid

Question 24

What is the most common structure motif in membrane proteins?

Answer 24

Membrane-spanning alpha-helices

Question 25

Bacteriorhodopsin (BR)

Answer 25

Membrane protein light-driven proton pump - converts energy of light into transmembrane proton gradient that is used to synthesize ATP Made mostly of alpha-helices arranged perpendicular to the bilayer plane

Question 26

Cyclooxygenase (COX) 1 or Prostaglandin H2 synthase (PGHS) 1

Answer 26

Integral protein Binds to the luminal leaflet of the ER Primarily alpha-helices

Question 27

Lipids are ______ associated to the proteins

Answer 27

Covalently

Question 28

________ anchor their attached proteins to membrane and mediate protein-protein interactions

Answer 28

Lipids

Question 29

Three kinds of lipid-linked protein modification

Answer 29

Palmitoylation of cysteine residues by a thioester bond Farnesylation of cysteine residues at the C-terminus Glycosylphosphatidylinositol-link to the carboxyl terminus

Question 30

Farnesylation at the C-terminus

Answer 30

Covalent attachment of farnesyl unit to C-term. tetrapeptide CAAX in which Cys is followed by 2 aliphatic residues After thioether linkage w/ Cys residues, AAX tripeptide is hydrolytically cleaved away

Question 31

Glycosyl phosphatidylinositol (GPI) anchor

Answer 31

Anchors protein to outer leaflet of the plasma membrane | Many Cell-surface hydrolytic enzyme and adhesions are tethered to cells by a GPI unit

Question 32

Describe the structure of a mitochondrion

Answer 32

Two membrane systems: outer membrane and inner membrane | Two compartments: intermembrane space and matrix

Question 33

Where are the internal ridges, or cristae, located?

Answer 33

Inner membrane

Question 34

Where does oxidative phosphorylation take place?

Answer 34

Intermembrane space

Question 35

Where does most of the TCA cycle and fatty acid oxidation take place?

Answer 35

Matrix

Question 36

What is the outer membrane permeable to?

Answer 36

Most small molecules and ions

Question 37

What is the inner membrane permeable to?

Answer 37

Impermeable to nearly all ions and polar molecules

Question 38

What is the mitochondrial porin?

Answer 38

30-35 kDa pore-forming proteins known as Voltage-dependent anion channel on the outer membrane

Question 39

What type of metabolites are transported across the inner membrane?

Answer 39

Metabolites such as ATP, pyruvate, and citrate