Membrane Structure Flashcards
What type of molecules can traverse cell membranes without the aid of membrane protein? What type
have significant difficulty? What type almost never? What type absolutely cannot?
Small, nonpolar molecules = transverse without aid of membrane protein
Uncharged polar molecules = Significant difficulty
Larger uncharged polar molecules = Almost never
Ions = Absolutely cannot
Describe the structure of a phospholipid.
Phosphate-containing, hydrophilic (“water-loving”) head
Two hydrophobic (“water- fearing”) tails
What are the main macromolecular components of cell membranes?
- Lipids
- Proteins
- Cabrohydrates
What are three mechanisms that restrict membrane proteins to distinct membrane domains?
- Tight junctions
- Cytoskeletal proteins
- ECM proteins
(1) What is osmosis? (2) How can certain cell types relieve osmotic pressure?
(1) Osmosis - movement of water down its concentration gradient —from an area of low solute concentration (high water concentration) to an area of high solute concentration (low water concentration)
(2)
* Plant cells - have cell walls (resists pressure)
* Protists - expel water
* Animal cells - pump out solutes w/ membrane pumps
What is the general resting membrane potential of a cell? What processes contribute to this this state?
What is membrane fluidity? How does cholesterol, temperature and type of fatty acids within the
phospholipid influence membrane fluidity?
(1) Membrane fluidity -
(2)
Cholesterol:
- decrease fluidity at high temps
- increases fluidity at low temps
Temperature:
Type of fatty acids:
- Saturated = decrease fluidity
- Unsaturated = increase fluidity
Where in the cell are new membranes formed (which organelle? on the cytosolic or luminal face?)
Cytosolic surface of endoplasmic reticulum (ER)
What is the difference between scramblase and flippase? Where do they function in the cell?
Scramblase:
* Random
* Functions in ER
* No ATP
Flippase:
* Directional
* Functions in Golgi
* ATP dependent
Explain how and what type of proteins can strengthen the plasma membrane.
Cell cortex = cytoskeletal network beneath plasma membrane (e.g., spectrin, actin)
What are five distinct functions of membrane proteins?
- Transporters
- Ion channels
- Anchors
- Receptors
- Enzymes
(1) What are internal membranes? (2) What type of cell has them?
(1) Membranes that enclose organelles
(2) Eukaryotic cells
What are three ways the plasma membrane interacts with the surrounding environment?
- Receiving information: receptor proteins enable cell to receive signals from environment
- Import and export of small molecules: channels and transporters in membrane enable import and export of small molecules
- Capacity for movement and expansion: flexibility of membrane and its capacity for expansion allows cell to grow, change shape, and move
depend on membrane interacting with cytoskeleton (inside) and extracellular matrix (outside)
What are the roles of cell surface carbohydrates?
- Helps protect cell surface from mechanical damage
- Help lubricate cells (carbohydrates attract H2O)
- Cell-cell recognition
How are triaclyglcerols different from other lipids?
Entirely hydrophobic
What does amphipathic mean?
Molecules with both hydrophilic and hydrophobic parts
Describe the structure of transmembrane proteins.
- hydrophobic regions lie in interior of the bilayer
- hydrophilic regions are exposed to aqueous environment on either side of membrane
What are the different ways transmembrane proteins associated with the lipid bilayer?
- Single alpha-helix
- Multiple alpha-helices
- Rolled-up beta-sheet (Beta-barrel)
What is the difference between integral and peripheral membrane proteins.
Integral membrane proteins - directly attached to lipid bilayer
Peripheral membrane proteins - proteins attached to other membrane proteins
Compare single-pass and multi-pass transmembrane proteins.
Single-pass - crosses the membrane only once
Multi-pass - a series of α helices that cross the bilayer a number of times
(1) Describe the structure of a beta-barrel. (2) Give an example.
(1)
Hydrophilic amino acid side chains face inside of barrel
Hydrophobic amino acid side chains face outside of barrel
(2) Porins
What are detergents?
substance used to solubilize lipids and membrane proteins
What are two examples of detergents? Compare them.
- Sodium dodecyl sulfate (SDS)
- Strong ionic detergent
- Ionized (charged) group at hydrophilic end
- Denatures protein - Triton X-100
- Mild nonionic detergent
- Nonionized but polar structure at hydrophilic end
- Protein function can remain
Explain the three steps of how a membrane protein can be solubilized.
- Detergent micelle interacts with outer bilayer of membrane
- Membrane is solubilized (formation of protein-detergent complex and lipid-detergent complex)
- Protein is purified using affinity chromatography
What is spectrin?
Dimeric protein that is the main component of red blood cell cortex
What is the result of a mutation in spectrin?
Anemia in humans (RBCs are more spherical and less flattened)
Non RBCS have more of what protein in the cortex?
Actin
What is the difference between a glycolipid and a glycoprotein?
Glycolipid - lipid covalently attached to sugars
Glycoproteins - proteins with short chains of sugars
Explain the difference between hydrophilic and hydrophobic interactions with water.
Hydrophilic molecules attract water molecules (water soluble)
Hydrophobic molecules tend to avoid water (water insoluble)
What is the most common phospholipid in cell membranes?
Phosphatidylcholine
The lipid portion of the plasma membrane is primarily _______.
phospholipids
Which part of the membrane gives it specific characteristics and functions?
Embedded proteins
The lipid bilayer serves as a permeability barrier to what type of molecules?
Water-soluble molecules
What is the glycocalyx?
Carbohydrate layer; carbohydrate-rich zone on cell surface
All of the carbohydrate on the glycoproteins, proteoglycans, and glycolipids is located on the ______ of the plasma membrane.
Outside
Compare flippases and floppases.
Flippases - moves specific phospholipids from the lumenal to the cytosolic layer of the membrane
Floppases - move specific phospholipids in the opposite direction (from cytosolic to the lumenal side)
What are the two faces of cell membranes?
The cytosolic monolayer always faces the cytosol (inside face)
- The non cytosolic monolayer is exposed to either the cell
exterior (plasma membrane) or the interior lumen of an organelle (outside face)
