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Exam 4: The Structure and Function of the Plasma Membrane

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Question 51

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Why would the transmembrane portion of membrane proteins shown in the figure below be unlikely to be composed of an $\alpha$ -helix made of hydrophilic amino acids?

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The amino acids in the membran...

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Question 52

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You treat some cells with a proteolytic enzyme that is too large to penetrate the cell membrane (Set 1) .Another group of cells is made permeable before treatment with the enzyme (Set 2) .A third set of cells was not treated with the enzyme at all (controls) .Proteins are then extracted from the three different sets of cells and applied to an SDS-PAGE gel.Protein W migrates to the same distance on a gel of proteins from Set 1 and Set 2;Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells.Protein X migrates to the same distance on a gel of proteins from control cells and the gels of the proteins from Set 1 and Set 2.Protein Y migrates a longer distance when extracted from Set 1 cells than does protein Y in the controls;Protein Y moves an even larger distance in the gel of the extracts from Set 2.Protein Z migrates the same distance on gels of proteins from the controls and the proteins extracted from Set 1,but it migrates a longer distance in extracts from Set 2 cells.Which protein is exposed only on the exterior of the cell?

A) Protein W
B) Protein X
C) Protein Y
D) Protein Z
E) Protein K

F) B) and D)
G) B) and C)

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Question 53

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In the middle of the winter,the membranes from a tissue sample from an organism dwelling in a pond are analyzed for their phospholipid content.In the middle of the summer,another tissue sample is taken from the same type of organism and the membrane lipid content determined.The lipid content has changed.How has it changed and why?

Why would flip-flop of membrane phospholipids as seen in the figure below be so rare?

The movement of water through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration is called ________.

What technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane?

Long-term potentiation is associated with NMDA receptors,one of several types of receptors that bind to the excitatory neurotransmitter _______.Its binding opens an internal cation channel within the receptor that allows _____ influx into the postsynaptic neuron,triggering a cascade of biochemical changes that lead to synaptic strengthening.

What happens to phospholipid mobility when the cell is treated with agents that disrupt the underlying membrane skeleton?

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 ________.

What amino acid is made to replace another amino acid in membrane-spanning $\alpha$ -helices by site-directed mutagenesis of the gene coding for the protein? This is done in order to determine how close together two such $\alpha$ -helices are in the structure of an integral protein.The amino acid is added to facilitate the formation of crosslinks between $\alpha$ -helices that are in close proximity.

Which of the following is not a function of peripheral proteins?

You determine the transition temperatures for two membranes.The first has a transition temperature of 28°C,the second a transition temperature of 15°C.What can you conclude about the compositions of the two membranes?

Which protein in the red blood cell membrane appears to be responsible for the exchange of bicarbonate ions and chloride ions across the red blood cell membrane?

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

What evidence convinced Overton that membranes were composed of lipids?

Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein,which helps the process along,is called ________.

People with the most severe cases of CF transport no chloride ions,while people with less severe cases transport some Cl- ions.What is a possible explanation of this?

The temperature at which a lipid bilayer shifts from a fluid state to a crystalline gel is called the _____.

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

Phosphatidylethanolamine is concentrated in the inner leaflet of the plasma membrane and tends to promote the curvature of the membrane,which is important in _________.