8/28/14 - Membrane Structure & Function

Question 1

How does a double bond influence fatty acid structure?

Answer 1

Double bonds induce a kink that prevents phosphoglycerides from packing too tightly.

Question 1

What is membrane fluidity?

Answer 1

The relative mobility of lipids within a membrane

Question 3

What percentage of cell membranes is made of proteins and lipids?

Answer 3

Usually 50%/50%, although depending on the cell type, protein composition can range from 25-75%.

Question 4

What is a structural aspect of lipid bilayers that is critical for many biological processes?

Answer 4

Assymetry, because it allows compartmentalization of processes.

Question 5

What are lipid rafts?

Answer 5

Free-floating membrane microdomains rich in cholesterol and sphingolipids that organize cellular activity.

Question 5

What is a secondary structure commonly found spanning a lipid bilayer?

Answer 5

Alpha helices with hydrophobic residues throughout

Question 5

What is the immunological synapse?

Answer 5

Cell to cell contact induces clustering of cellular membrane components at the point of contact

Question 6

Would you expect the inside of a beta barrel structure to have many hydrophilic or hydrophobic residues?

Answer 6

Hydrophilic, since these structures often function as channels through which molecules can enter the cytosol from the extracellular space.

Question 7

Describe the general structure of phosphoglycerides?

Answer 7

A glycerol molecule has two fatty acid chains bound to adjacent carbons and a phosphatidyl group bound to the 3rd carbon.

Question 9

What is the maximum ratio of cholesterol to phospholipids in a cell membrane?

Answer 9

1:1

Question 10

Why was the formation of a lipid bilayer conducive to the formation of life?

Answer 10

It allowed for a barrier to form between the interior of the cell and the exterior environment. This formation of a sealed compartment is energetically favorable due to self-aggregation.

Question 11

How is fluidity related to transition temperature?

Answer 11

The higher the fluidity, the lower the transition temperature.

Question 12

What role does phosphatidyl serine play in membrane structure and function?

Answer 12

It creates a negative charge on the interior of the cell membrane compared to the outer membrane.

Question 13

What feature of membrane proteins do FRAP experiments demonstrate?

Answer 13

Membrane proteins diffuse laterally within the plasma membrane.

Question 14

What 4 ways do phospholipids move through lipid membranes?

Answer 14

1. Lateral diffusion 2. Flexion (pendulum-like movement) 3. Rotation 4. Flip flop (rare)

Question 15

What are 3 ways a membrane protein can associate with the cytoplasmic leaflet of the plasma membrane?

Answer 15

1. Myristoyl anchor via amide linkage 2. Palmitoyl anchor via thioester linkage 3. Farnesyl anchor via thioester linkage

Question 15

What is a membrane leaflet?

Answer 15

One layer of the lipid bilayer.

Question 16

What is the effect of cholesterol incorporation into a lipid bilayer?

Answer 16

It increases the rigidity of the membrane and decreases the permeability of the bilayer to water soluble molecules

Question 17

What does a hydropathy plot show?

Answer 17

It shows the hydrophobicity of an entire amino acid chain. Positive peaks correspond with hydrophobic regions that most likely span the membrane.

Question 18

How can galectin 3 be used for imaging? (important)

Answer 18

Galectins contain a carbohydrate recognition domain that allows them to bind sugars on cell surface proteins. Gal3 is normally found in cytoplasm, where no sugars are accessible because glycosylation is rare. When a pathological agent ruptures organelles such as phagosomes, endosomes, or lysosomes, the sugars normally present on the inside of the vesicle become accessible to Gal3. Gal3 binds to those sugars, and can then be visualized to determine where in a cell a pathological agent attacks.

Question 20

What molecules are found only on the exterior surface of the cell membrane?

Answer 20

Glycolipids

Question 21

How does the presence of double bonds in a fatty acid tail influence the transition temperature of a lipid?

Answer 21

Double bonds create kinks in phospholipid tails, which increases fluidity and decreases transition temperature.

Question 23

What does translocation of the membrane-bound PS protein cause?

Answer 23

PS proteins mark the cell for degradation by macrophages after apoptosis is initiated. A scramblase enzyme flips the PS protein from the intracellular to extracellular side following initiation of apoptosis.

Question 24

What features of fatty acid tails determine membrane fluidity?

Answer 24

Length and degree of saturation.

Question 25

Describe self-aggregation of lipid molecules.

Answer 25

Amphiphilic molecules organize themselves so that the hydrophilic portions are in contact with water and the hydrophobic portions are not.

Question 26

How will the length of a fatty acid tail influence the transition temperature?

Answer 26

The shorter the tail, the lower the transition temperature.

Question 27

What is the function of phospholipase C?

Answer 27

Cleaves inositol phospholipids to generate relay signals and scaffolds for protein kinase C.