Lecture 2 - Membranes I: Structure and Function

Question 1

Important plasma membrane characteristics

Answer 1

Bilayer - inner and outer leaflet

Studded with proteins and carbohydrates

Question 2

Percentages of chemical components of most membranes

Answer 2

A little less than 50% protein, a little less than 50% lipid, and a small amount of carbohydrate, but this can change depending on the function of the membrane

Question 3

True or False: Lipids are asymmetrically distributed in the membrane.

Answer 3

True

Question 4

Which leaflet of the plasma membrane is generally more fluid than the other? Why is this important?

Answer 4

The outer leaflet. This allows for lipid rafts to to rapidly concentrate ligand-receptor pairs at specific sites on the membrane for internalization.

Question 5

What are the four classes of lipids?

Answer 5

Phospholipids, Sphingolipids, Cholesterol, Eicosanoids

Question 6

What are three classes of eicosanoids?

Answer 6

Prostaglandins, Thromboxanes, and Leukotrienes

Question 7

What is the major functions of PGE2?

Answer 7

Intrauterine contractions, vasodilation, platelet aggregation (regulation of vascular tone, smooth muscle contractility)

Question 8

What are the major functions of TXA2?

Answer 8

Induces platelet aggregation, vasoconstriction

Question 9

What are the major functions of LTC4, LTD4, and LTE4?

Answer 9

Induce vasodilation and bronchoconstriction in asthma, components of SRS-A (slow-reacting substance of anaphylaxis)

Question 10

What is an important property of phospholipids?

Answer 10

Fusogenicity

Question 11

True or False: The more kinked phospholipids a membrane has the more rigid it will be?

Answer 11

False

Question 12

What are two diseases that take advantage of the fusogenic properties of plasma membranes?

Answer 12

HIV

Measles

Question 13

True or False: Sphingolipids have fusogenic properties.

Answer 13

False

Question 14

True or False: The head groups of sphingolipids are different from phospholipids?

Answer 14

True

Question 15

What are three important sphingolipid metabolism diseases?

Answer 15

Fabrys
Gaucher
Tay-Sachs

Question 16

Sphingolipid metabolism diseases are a subset of what type of disease?

Answer 16

Lysosomal Storage Diseases (LSDs)

Question 17

What factors affect membrane fluidity?

Answer 17

1. Double bonds, more double bonds = kinkier and more fluid
2. Acyl chain length, shorter acyl chains = more fluid
3. Temperature, higher temperature = more fluid
4. Cholesterol, at body temperature, higher cholesterol = less fluid

Question 18

What do mycoplasma do in the respiratory tract?

Answer 18

They attach to the base of columnar epithelial cells in respiratory cilia and extract the cholesterol from the plasma membranes for their own metabolic purposes rendering the cilia ineffective in moving mucous and pathogens out of the respiratory tract because their membranes are too fluid for them to function properly.

Question 19

Lipid rafts

Answer 19

Specialized cholesterol- and sphingolipid-rich microenvironment in the membrane that move rapidly within a leaflet; they are more stiff than the surrounding membrane

Question 20

What are lipid rafts critical for?

Answer 20

1. Signal transduction
2. Endocytosis
3. Rapid reorganization of the membrane for extracellular matrix modification and motility

Question 21

In which leaflet are lipid rafts more likely to be found?

Answer 21

The outer leaflet

Question 22

Glycophorin

Answer 22

Simple single membrane-spanning segment protein

Question 23

Key points of transmembrane proteins

Answer 23

1. It takes 20-25 aa to span the membrane.

2. Nearly all the aa in a membrane-spanning segment are hydrophobic.

Question 24

Band 3 Protein

Answer 24

Anion exchanger in RBCs; multifunctional protein; has 14 membrane-spanning segments that form a ring with a gap in the middle through which the anion goes

Question 25

Functions of carbohydrates in plasma membranes

Answer 25

1. blood-type antigens
2. pathogen recognition sites
3. reservoir for cytokines and growth factors

Question 26

Which part of proteoglycans and glycoproteins do the work?

Answer 26

The carbohydrate

Question 27

What does coccidia recognize?

Answer 27

Specific carbohydrates on the intestinal epithelial cell surface

Question 28

How can you tell if infection with toxoplasma gondii is a result of a contaminated food or water source in specific patients?

Answer 28

Whether or not patients complain of discomfort in the upper or lower GI tract