Lecture 5

Question 1

How are phospholipids categorized?

Answer 1

Based on their head group

Question 2

What is a sphingolipid?

Answer 2

Phospholipid with a sphingosine instead of a glycerol

Question 3

What are the functions of cholesterol?

Answer 3

• Stiffens membrane, making it less fluid and less permeable

- Prevents hydrocarbon tails of phospholipids from packing –> decreases crystal formation

Question 4

In a fluid state, are there more saturated or unsaturated FAs?

Answer 4

Unsaturated FAs

Question 5

In a gel-like state, are there more saturated or unsaturated FAs?

Answer 5

Saturated FAs

Question 6

Define amphipathic.

Answer 6

Is both hydrophobic and hydrophilic

Question 7

What are the features of the Fluid Mosaic Model?

Answer 7

• Proteins are not just arranged along the surface, but are also embedded in the lipid bilayer –> mosaic of lipids and proteins in the membranes
• Molecules including lipid and proteins can move laterally (are freely diffusing) in the membrane –> membrane is not solid, but more like a fluid

Question 8

Are proteins static or dynamic?

Answer 8

Dynamic, for the most part

Question 9

What is FRAP? Function?

Answer 9

Fluorescence recovery after photobleaching = used to study lateral movements of proteins w/in the membrane

Question 10

How does FRAP work?

Answer 10

1. High-powered laser is used to bleach a particular region in a cell expressing the protein of interest –> region loses its fluorescence
2. W/ time, unbleached protein moves in and bleached protein moves out of region –> gains back its fluorescence

Question 11

How can you tell how fast a protein is moving using FRAP?

Answer 11

• Fluorescence recovers fast –> protein is very dynamic

- Fluorescence recovers slow –> protein is very stable and anchored in place

Question 12

What is a single pass membrane? What does it look like on a hydrophobicity plot?

Answer 12

• Protein that passes through membrane one time

- Plot: only one peak above 0 (in hydrophobicity range)

Question 13

What is a multipass membrane protein? What does it look like on a hydrophobicity plot?

Answer 13

• Protein that passes through a membrane multiple times

- Plot: as many peaks above 0 as there are passes through the membrane

Question 14

What is a lipid/GPI-anchored membrane protein?

Answer 14

Protein made inside the cell, but displayed outside the cell and anchored to membrane by a GPI anchor

Question 15

Where and when does acylation occur?

Answer 15

2nd position of a protein after synthesis is complete

Question 16

Which terminus is away from the membrane in acylation?

Answer 16

C-terminus

Question 17

Which terminus is away from the membrane in prenylation?

Answer 17

N-terminus

Question 18

What is a giveaway that prenylation has occurred?

Answer 18

CxxC (cysteine sandwich)

Question 19

What does trypsin do?

Answer 19

Chops up the extracellular domains of any proteins imbedded in the plasma membrane

Question 20

What is the effect of trypsin treatment on western blot analysis of that protein?

Answer 20

After treatment, only the parts of the protein inside the membrane will remain –> protein will be smaller and move toward the (+) anode faster

Question 21

Glucose is moved into intestinal epithelial cells against its concentration gradient using the potential energy of _____ established through the _____.

Answer 21

• Na+ ion gradient

- Na+/K+ ATPase pump

Question 22

You isolate a loss of function mutation in a bacterial gene that codes for a fatty acid desaturase. You are now proposing to analyze membranes from this mutant strain of bacteria. What do you expect to find?

Answer 22

A decrease in the number of carbon double bonds and a decrease in membrane fluidity.