Lecture 11: Biomembranes

Question 1

What are four basic features of biomembranes?

Answer 1

1. Phospholipid Bilayer
2. Embedded Proteins
3. Non Covalent Membranes (fluidity)
4. Membrane Flexibility

Question 2

What form are most of the carbohydrates in biomembranes?

Answer 2

Glycoproteins or Glycolipids

Question 3

What are molecules w/both hydrophobic and hydrophilic regions?

Answer 3

Amphipathic

Question 4

If the cross sectional area of the polar group is greater than that of the acyl side chain, what is likely to form?

Answer 4

Micelles

Question 5

What causes liposomes to form spontaneously?

Answer 5

the unstable edges of the lipid bilayer

Question 6

What are the most abundant lipids in cell membranes?

Answer 6

Phospholipids

Question 7

What is the general structure of phospholipids?

Answer 7

Phosphate (polar head) + Glycerol + Hydrocarbon Chains of the Fatty Acid (non polar)

Question 8

These lipids contain sphigosine.

What is sphingosine?

What is an example found in the neuron?

Answer 8

Sphingolipids

Amino-alcohol

Sphingomyelin

Question 9

This amphipathic sterol is vital for regulation of the biomembrane’s fluidity.

Answer 9

Cholesterol

Question 10

What are the major phospholipids found on the outer leaflet?

Answer 10

phosphatidylcholine

sphingomyelin

glycolipids

Question 11

What are the major phospholipids found on the inner leaflet?

Answer 11

phosphatidylethanolamine

phosphatidylserine

phosphatidylinositol

Question 12

Do all membranes have a uniform distribution of lipids?

Answer 12

No, different membranes have unique lipid distributions

Question 13

What is the general process for generating lipid bilayers in lab?

Answer 13

1. Treat w/organic solvent
2. Remove insoluble protein, oligosaccharide residues
3. Evaporate solvent
   4a. Rehydrate in water
   4b. Rehydrate in water w/planar bilayer

Question 14

Why is the study of liposomes relevant for disease?

Answer 14

Artificially constructed liposomes can be filled with drugs and used as a delivery system in the treatment of disease

Question 15

Why are individual lipids able to diffuse laterally rapidly?

Answer 15

The bilayer is held together by noncovalent forces

Question 16

What is the result of low Temp on a phospholipid bilayer?

Answer 16

Gel-like consistency

Less Fluid

Thicker diameter

Question 17

What is the result of high Temp on a phospholipid bilayer?

Answer 17

Fluid-like consistency

More Fluid

Thinner diameter

Question 18

How is membrane fluidity regulated?

Answer 18

Altering membrane composition (proteins, cholesterol, etc)

Question 19

What affect does Cholesterol have on the bilayer in high and low T?

What is this termed?

Answer 19

High: Decreased membrane fluidity; attraction to cholesterol pulls them closer

Low: Increased membrane fluidity; increase distance between phospholipids

Paradoxical

Question 20

What is the effect of fatty acyl chain saturation on fluidity?

How could this be manipulated?

Answer 20

Saturated: Easier to pack, less fluid

Unsaturated (kinked): Harder to pack, more fluid

You could use a desaturase enzyme to decrease fluidity (or vise versa)

Question 21

What is the effect of fatty acyl chain length on fluidity?

How could this be manipulated?

Answer 21

Longer Tail: Less Fluid

Shorter Tail: More Fluid

You could use an enzyme to alter tail length

Question 22

What are localized regions of the membrane enriched with cholesterol, sphingolipids, and saturated phospholipids called?

What important class of glycoproteins are found here?

Why are they important?

Answer 22

Lipid rafts

GPI-anchored proteins

Lipid rafts and ^ likely play a role in signal transduction

Question 23

What does phospholipid synthesis occur?

What ensures even growth of both halves of the lipid bilayer?

Answer 23

The cytostolic surface of the Endoplasmic Reticulum (ER) membrane

Lipid translocators called Flippases

Question 24

How to phospholipids reach their final membrane destination?

Are they static during their journey?

What are formed while passing through Golgi apparatus?

Answer 24

Membrane trafficking via budding off and fusing

No, they are modified in other cellular compartments, example sphingomyelins and glyolipids are formed as vesicles pass through Golgi Apparatus

Question 25

What lipids are localized mainly on the extracellular leaflet? What lipids are localized mainly on the cytostolic leaflet? What does this MX require? What lipid may play a role in apoptosis signaling?

Answer 25

Extracellular: phosphatidylcholine, sphingomyelin Cytostolic: phosphatidylathanolamine, phosphatidylserine Energy Movement of phosphatidylserine to external surface for signaling with macrophages

Question 26

As vesicles bud and fuse during traficking, what is the result of the faces (direction) of the membranes?

Answer 26

They are conserved

Question 27

Describe uncatalyzed movement of phospholipids.

Answer 27

Lateral diffusion = fast (microseconds) Transbilayer = slow (days)

Question 28

Describe catalyzed movement of phospholipids. What do these require? What catalyzed movement does not require the answer above?

Answer 28

Flippases/Floppases move lipids transbiolayer They require ATP Scramblases move along a concentration gradient, and do not require energy

Question 29

What are the two major classes of membrane proteins? How are these bound? What would be the result of removing these from the bilayer?

Answer 29

Integral - covalent - bilayer destruction Peripheral - non-covalent - no disruption to bilayer

Question 30

What are the two structures of transmembrane proteins?

Answer 30

Most are alpha-helices composed of hydrophobic residues; if zig zag across will have both residues Beta barrels are less common, but form porins for small molecules to transverse; found in mitochondria and some bacteria

Question 31

How are integral proteins attached to the plasma membrane? What are three major locations and respective methods for these?

Answer 31

Lipid Anchors Cytoplasmic - single covalent linkage between fatty acid acyl chain and N-terminal glycine in protein Cyostolic - thioester bond between thiol group in cystein near c-terminus of peptide and hydrocarbon anchor Exoplasmic - complex glycosylated phospholipid linked to C-terminus of protein; GPI example

Question 32

What are two experimental methods for evidence of protein mobility?

Answer 32

Human-Mouse Cell Hybrid Label-Laser-Measure Experiment (quantitative)

Question 33

What conditions limit protein mobility?

Answer 33

``` Protein-Protein interaction in membrane (self) Adjacent cell protein (other) Cytoskeletal interactions (in-cell) Extracellular interactions (out-cell) ```

Question 34

What is the importance of membrane glycoproteins? What is glycocalyx?

Answer 34

Cell-to-cell recognition; such as selectin binding with oligosaccharides in the inflammatory response of would healing Glcocalyx is the carbohydrate coating of the outer surface which extends into the extracellular space