BIOL 102 Quiz 2

T/F) The microscopic method of measuring rates of fluorescence recovery of fluorescently-tagged membrane lipids after photobleaching (FRAP) is used to measure rates of membrane lipid movement from one bilayer leaflet to the other (flip flop).   

False

Factors that increase lipid bilayer fluidity include:

Select all that apply. 

• Decreased temperature

• Shorter hydrocarbon/fatty acid tails

• Increased unsaturation of hydrocarbon/fatty acid tails

• Shorter hydrocarbon/fatty acid tails

• Increased unsaturation of hydrocarbon/fatty acid tails

Select all that apply to lipid rafts in the cell's plasma membrane.

• Lipid rafts are enriched in cholesterol

• Lipid raft bilayers are thinner than the surrounding non-raft regions of the same leaflet

• Lipid rafts are enriched in cholesterol

(T/F) On average, the membrane spanning, hydrophobic alpha helices of integral membrane proteins are ~ 40 amino acids in length.

False

Some features of plasma membrane trans-bilayer asymmetry include:

Select all that apply. 

• Exclusive presence of phosphatidyl inositol lipids in the outer leaflet of the bilayer.

• Exclusive presence of glycolipids in the inner leaflet of the lipid bilayer.

• Exclusive presence of the negatively charged phospholipid phosphatidyl serine in the inner leaflet of the lipid bilayer.

• Exclusive presence of the negatively charged phospholipid phosphatidyl serine in the inner leaflet of the lipid bilayer.

(T/F) Peripheral membrane proteins associated with the extracellular surface of a cell can be selectively extracted/solubilized from the cell surface by treatment of intact cells with buffers that disrupt non-covalent protein-protein interactions such as high or low salt.

True

The lateral movement of integral membrane proteins of the cell’s plasma membrane can be restricted/restrained through— 

Select all that apply. 

• Lateral aggregation of membrane proteins within the plane of the membrane.

• Association with components of the extracellular matrix

• Association with components of the cell’s cytoskeleton

• Association with polyribosomes bound to the cytoplasmic surface of the plasma membrane.

• Lateral aggregation of membrane proteins within the plane of the membrane.

• Association with components of the extracellular matrix

• Association with components of the cell’s cytoskeleton

(T/F) To purify an integral membrane protein like the Na⁺/K⁺ ATPase/pump with the final goal of reconstituting the purified protein into liposomes (synthetic vesicles that can be made in the lab by adding phospholipids into an aqueous environment) so that its activity can be analyzed in the absence of other factors originally present in the plasma membrane, one of the first steps is to solubilize this multi-subunit integral membrane protein using a non-denaturing non-ionic detergent. 

True

Ion channels can be opened and closed (gated) by...

Select all that apply. 

• Blockage by a larger ion of the same charge (ion gated)

• Change in voltage across the membrane (voltage gated)

• Response to tension on the membrane (mechanically gated)

• Binding of specific ligands to the extracellular or intracellular domain of the channel (ligand gated)

• Change in voltage across the membrane (voltage gated)

• Response to tension on the membrane (mechanically gated)

• Binding of specific ligands to the extracellular or intracellular domain of the channel (ligand gated)

(T/F) Facilitated diffusion transporters like the glucose uniporter on the basolateral membrane of the intestinal epithelial cell move solutes across the membrane against the solute’s concentration gradient across the membrane. 

False

(T/F) In the intestinal epithelial cell, movement of solutes like glucose across membranes against a glucose concentration gradient by the Na⁺ /glucose cotransporter  (i.e. movement of extracellular glucose in the gut lumen where the concentration is low into the cell cytoplasm where glucose concentration is high) requires the hydrolysis of ATP by the  Na⁺ /glucose cotransporter.

False

(T/F) Cholesterol in membrane lipid bilayers reduces the mobility of the upper (nearest to lipid polar head group) regions of the hydrocarbon tails on bilayer lipids to which the cholesterol steroid rings are adjacent.

True

Gorter and Grendel extracted lipids from human red blood cells. They calculated the total surface area for these red blood cell lipids and found it to be 36 µm². How much surface area would these lipids cover once they were spread across the surface of water?

72 µm^2

What are the building blocks of a phosphoglyceride?

glycerol + 1 phosphate group + 2 fatty acids

What word describes a molecule that contains both hydrophilic and hydrophobic portions?

amphipathic

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

integral protein

What kind of membrane protein is found almost entirely outside the bilayer on either the extracellular or cytoplasmic surface and is covalently linked to a membrane lipid situated within the bilayer?

lipid-anchored protein

What characterizes the amino acids that are found in an α-helical segment that spans a membrane?

predominantly hydrophobic

In colder weather, a bird’s cells would need to __________________ in order to best modify the fatty acid composition of lipid membranes and maintain membrane fluidity homeostasis.

both an increase in incorporation of unsaturated fatty acids and a decreased incorporation of saturated fatty acids would be optimum

When membrane lipids are extracted from cells and used to prepare artificial lipid bilayers, cholesterol and sphingolipids (another type of membrane lipid that tend to have long saturated fatty acid tails) tend to self-assemble into ________ that are more gelated and highly ordered than surrounding regions consisting primarily of _________.

lipid rafts, phosphoglycerides

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence).

What does the cell look like immediately after fusion?

The cell is half red and half green.

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence).

What does the cell look like after one hour?

The red and green labels are uniformly distributed across the entire membrane.

T/F The inner leaflet of the plasma membrane lipid bilayer faces the cytoplasm.

True

A channel that opens in response to changes in ionic charge across a membrane is called a ________.

voltage-gated channel

A channel that opens in response to the binding of a specific molecule, which is usually not the solute that passes through the channel is called a ________.

ligand-gated channel

An important aspect of transport by facilitated transporters and pumps is ________.

conformational shifts in structure

The sodium-potassium pump makes the cell interior more negative by pumping _______ sodium ions out of the cell for every ___________ potassium ions pumped in.

3, 2

 In the Na⁺/glucose cotransporter, _________ moving down its gradient drives the transport of __________ against its gradient.

Na+ ions, glucose

What is thought to cause the 1 ms inactive time after a sodium ion channel initiates an action potential (membrane is depolarized)?

the presence of an inactivating peptide in the opening of the channel pore