Lecture 2 - Membranes I: Structure and Function Flashcards
Important plasma membrane characteristics
Bilayer - inner and outer leaflet
Studded with proteins and carbohydrates
Percentages of chemical components of most membranes
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
True or False: Lipids are asymmetrically distributed in the membrane.
True
Which leaflet of the plasma membrane is generally more fluid than the other? Why is this important?
The outer leaflet. This allows for lipid rafts to to rapidly concentrate ligand-receptor pairs at specific sites on the membrane for internalization.
What are the four classes of lipids?
Phospholipids, Sphingolipids, Cholesterol, Eicosanoids
What are three classes of eicosanoids?
Prostaglandins, Thromboxanes, and Leukotrienes
What is the major functions of PGE2?
Intrauterine contractions, vasodilation, platelet aggregation (regulation of vascular tone, smooth muscle contractility)
What are the major functions of TXA2?
Induces platelet aggregation, vasoconstriction
What are the major functions of LTC4, LTD4, and LTE4?
Induce vasodilation and bronchoconstriction in asthma, components of SRS-A (slow-reacting substance of anaphylaxis)
What is an important property of phospholipids?
Fusogenicity
True or False: The more kinked phospholipids a membrane has the more rigid it will be?
False
What are two diseases that take advantage of the fusogenic properties of plasma membranes?
HIV
Measles
True or False: Sphingolipids have fusogenic properties.
False
True or False: The head groups of sphingolipids are different from phospholipids?
True
What are three important sphingolipid metabolism diseases?
Fabrys
Gaucher
Tay-Sachs
Sphingolipid metabolism diseases are a subset of what type of disease?
Lysosomal Storage Diseases (LSDs)
What factors affect membrane fluidity?
- Double bonds, more double bonds = kinkier and more fluid
- Acyl chain length, shorter acyl chains = more fluid
- Temperature, higher temperature = more fluid
- Cholesterol, at body temperature, higher cholesterol = less fluid
What do mycoplasma do in the respiratory tract?
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.
Lipid rafts
Specialized cholesterol- and sphingolipid-rich microenvironment in the membrane that move rapidly within a leaflet; they are more stiff than the surrounding membrane
What are lipid rafts critical for?
- Signal transduction
- Endocytosis
- Rapid reorganization of the membrane for extracellular matrix modification and motility
In which leaflet are lipid rafts more likely to be found?
The outer leaflet
Glycophorin
Simple single membrane-spanning segment protein
Key points of transmembrane proteins
- It takes 20-25 aa to span the membrane.
2. Nearly all the aa in a membrane-spanning segment are hydrophobic.
Band 3 Protein
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
Functions of carbohydrates in plasma membranes
- blood-type antigens
- pathogen recognition sites
- reservoir for cytokines and growth factors
Which part of proteoglycans and glycoproteins do the work?
The carbohydrate
What does coccidia recognize?
Specific carbohydrates on the intestinal epithelial cell surface
How can you tell if infection with toxoplasma gondii is a result of a contaminated food or water source in specific patients?
Whether or not patients complain of discomfort in the upper or lower GI tract
