Lecture 16- Biological Membranes

Question 1

What are the 2 major components of all membranes?

Which composes a majority of a membrane?

Answer 1

Lipids and Proteins

Lipids

Question 2

Functions of a Biological Membrane:

1. ​Defines _______ boundaries of a cell
2. Controls molecular ______ across boundary
3. Divide cells (_______) into ____________
4. Organizes ________ sequences
5. ____-to-____ communication
6. Matrix for _________, ________, _________ molecules
7. ________ transduction w/in cell (________, ________)

Answer 2

Functions of a Biological Membrane:

1. ​Defines external boundaries of a cell
2. Controls molecular traffic across boundary
3. Divide cells (eukaryotes) into compartments
4. Organizes reaction sequences
5. Cell-to-Cell communication
6. Matrix for transporters, receptors, adhesion molecules
7. Energy transduction w/in cell (mitochondria, chloroplasts)

Question 3

Amount of Å a lipid portion of a bilayer is?

2 monolayers of a bilayer?

Answer 3

30 Å

Leaflets

Question 4

1 wedge-shaped fatty acid tail consisting of a fatty acid/lysolipids

Answer 4

Micelle

Question 5

2 cylindrical fatty acid tails (Glyerophospholipids, Sphingolipids)

Combo above that contains an aqueous cavity

Answer 5

Bilayer

Vesicles

Question 6

Concentration of lipid req’d for micelle formation

Answer 6

Critical Micelle Formation

Question 7

What do the formation of micelles depend on? (3)

Answer 7

Temp, lipic concentration & lipid composition

Question 8

What is a vesicle prepared from purified lipid?

Answer 8

Liposome

Question 9

T/F: Lipid composition of all cell membranes is the same.

(Explain)

Answer 9

False: Lipid composition of cell membranes is different depending on organelle and function.

Question 10

LIpid composition of bilayer leaflets is (bisymmetrical/asymmetrical) w/ _______ lipids and/or ________ on the ________ leaflet.

Answer 10

LIpid composition of bilayer leaflets is asymmetrical w/ neutral lipids and/or glycolipids on the external leaflet.

Question 11

What kind of model best describes biological membranes?

This can be described as a non-rigid, complex mixture of _______ & ________ molecules ______ in bilayer

Answer 11

Fluid Mosaic Model

This can be described as a non-rigid, complex mixture of lipids & protein molecules floating in bilayer

Question 12

The interior of a bilogical membrane is consisted of _____ ______ that forms a _____, ___________ region.

Answer 12

The interior of a bilogical membrane is consisted of fatty acyl (C-H) that forms a fluid, hydrophobic region.

Question 13

___________ interactions of ____ side-chains hold membrane proteins together.

Answer 13

Hydrophobic interactions of AA side-chains hold membrane proteins together.

Question 14

What type of membrane proteins are the site of hydrophobic AA interaction and are only reremovable by hydrophobic agents (EX?)

Answer 14

Integral Membrane Proteins (Removable by hydrophobic agents: detergents, organic solvents, denaturants)

Question 15

What type of membrane proteins associate with electrostatic interactions with H-bonding and how are they released?

Answer 15

Peripheral (mild detergents/interference w/ charge or H-bonding)

Question 16

What type of membrane proteins is located in the cytosol that can associate/dissocate thru electrostatic interactions/lipid tails? (EX)

Answer 16

Amphitropic Proteins

(Covalent/Noncovalent = Lipidation, phosphorylation, ligan binding)

Question 17

What is the localization of proteins relative to the lipid bilayer and how can it be assessed?

Answer 17

Membrane Protein Topology, analysis of AA sequence

Question 18

What are common transmembrane motifs within membrane protein topology?

What do proteins have that is important to distinguish its function?

Answer 18

Alpha helices and Beta-strands

“Sidedness”

Question 19

For protein-lipid interactions, how are membrane proteins classified? (4)

Answer 19

Sidedness, # of transmembrane (TM) helices, # polypeptides, lipid modifications

Question 20

Type of protein-lipid interaction that has a single TM helix & Amino-terminus on the outside?

Answer 20

Type 1

Question 21

Type of protein-lipid interaction that contains a single, TM helix & carboxy-terminus on the outside?

Answer 21

Type 2

Question 22

Type of protein-lipid interaction that contains multiple TM helices?

Answer 22

Type 3

Question 23

Type of protein-lipid interaction that contains multiple, polypeptides that assemble to form protein complexes?

Answer 23

Type 4

Question 24

Type of protein-lipid interaction that is attached to the bilayer primarily by lipid modification?

Answer 24

Type 5

Question 25

Type of protein-lipid interaction that contains BOTH terminal helices and lipid anchors?

Answer 25

**Type 6**

Question 26

\_\_\_\_\_\_\_\_\_\_\_\_: Type 3 Integral Membrane Protein * Salt-loving bacteria similar to light-driven molecule in ___ that absorbs protons * __ TM helices connected by the inner non-helical loops & outer face membrane * Anchored by hydrophobic ____ \_\_\_\_\_ interactions with \_\_\_\_\_\_\_

Answer 26

**Bacteriohodopsin**: Type 3 Integral Membrane Protein * Salt-loving bacteria similar to light-driven molecule in **eye** that absorbs protons * **7** TM helices connected by the inner non-helical loops & outer face membrane * Anchored by hydrophobic **side chain** interactions with **lipids**

Question 27

_Predicting Secondary Structure of Membrane Spanning Portions of Integral Membrane Protein:_ * Alpha-helix: ___ Å rise/residue * 30 Å hydrophobic interior req's __ AA * TM helices ~\_\_ turns long

Answer 27

_Predicting Secondary Structure of Membrane Spanning Portions of Integral Membrane Protein:_ * Alpha-helix: **1.5** Å rise/residue * 30 Å hydrophobic interior req's **20** AA * TM helices ~**6-7** turns long

Question 28

What is the amount of energy it takes to move an R group from the hydrophobic to hydrophilic area? (Delta G)

Answer 28

**Hydropathy Index**

Question 29

For a hydropathy index, a (+)Delta G requires energy, which indicates a __________ group.

Answer 29

**hydrophobic**

Question 30

Type of graph? Label the axes.

Answer 30

A Hydropathy plot contains successive windows of sequence with the calculated **hydropathy** **index** and then its **residue** number plotted against it.

Question 31

What are aromatic residues found @ the interface of water and lipids? Name 2 that are also found bw exterior & interior, and @ border.

Answer 31

**Membrane Interface Anchors** **Tyrosine (Y)** & **Tryptophan (W)**

Question 32

_Positive-Inside Rule for Membrane Proteins:_ * (-) charged lipids are usually on the ______ leaflet (phosphotidylserine/phosphotidylinositol) * Favors (+) charged AA (\_\_\_, \_\_\_\_, \_\_\_\_) on the inside * Look for charge in ___________ regions to determine orientation

Answer 32

_Positive-Inside Rule for Membrane Proteins:_ * (-) charged lipids are usually on the **inner** leaflet (phosphotidylserine/phosphotidylinositol) * Favors (+) charged AA (**Lys (K)**, **Arg (R)**, **His (H)**) on the inside * Look for charge in **non-transmembrane** regions to determine orientation

Question 33

\_\_-\_\_\_\_\_\_\_\_: another structure found in integral proteins * ___________ inside barrel * ___________ outside barrel (touching \_\_\_\_\_\_) * Important for _______ transport, but hard to determine * \_\_\_\_\_\_\_: proteins that allow select polar solutes to cross membranes

Answer 33

**B-Strands--\> B-Barrel**: another structure found in integral proteins * **Hydrophilic** inside barrel * **Hydrophobic** outside barrel (touching **lipids**) * Important for **passive** transport, but hard to determine * **Porins**: proteins that allow select polar solutes to cross membranes

Question 34

\_\_\_\_\_\_\_\_\_\_\_\_\_ membrane proteins can associate w/ membranes by covalently attached lipids * Not integral/peripheral, but how are they attached? (aka?) * What is the strongest? (2x16C's) * _______ = Strength!

Answer 34

**Amphitrophic** membrane proteins can associate w/ membranes by covalently attached lipids * Not integral/peripheral, but **attached by anchors of lipid molecules to target proteins (posttranslational modification)** * Glycosylphosphatidlyinositol, **GPI is the strongest** (2x16C's) * **Length** = Strength!