cell bio smartwork ch.11

Shown is a schematic diagram of a membrane phospholipid. Which segment will always carry a negative charge?

B(second one) - represents the phosphate group, which is always negatively charged.

To study the structure of a particular membrane protein, the target protein is usually removed from the membrane and separated from other membrane proteins. Shown below are three different proteins associated with the cell membrane. Treatment with high salt would release which protein or proteins from the bilayer?

Correct. Treatment with high salt or changing the pH of the solution can disrupt protein-protein interactions. High salt would therefore release this peripheral membrane protein from the bilayer.The other proteins are integral membrane proteins; their attachment to the membrane would not be altered by salt alone.

Which membrane would show a more rapid recovery of fluorescence in a FRAP study?

FRAP is method used to measure the fluidity of a cell membrane. Membrane containing a larger proportion of unsaturated fatty acids are indeed more fluid; hence, they should exhibit a more rapid recovery in FRAP.

When scientists were first studying the fluidity of membranes, they did an experiment using hybrid cells. Certain membrane proteins in a human cell and a mouse cell were labeled using antibodies coupled with differently colored fluorescent tags. The two cells were then coaxed into fusing, resulting in the formation of a single, double-sized hybrid cell. Using fluorescence microscopy, the scientists then tracked the distribution of the labeled proteins in the hybrid cell.Which best describes the results they saw and what they ultimately concluded?

Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer. Correct. This is, indeed, what they saw. Although not all plasma membrane proteins diffuse quite so freely, the results of the hybrid experiment demonstrated that certain membrane proteins, like membrane lipids, can move laterally within the plane of the lipid bilayer.

Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but lipids can be labeled too.How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?

The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence. Consider the relative sizes of lipids and proteins and how this size difference might affect the relative speed at which these molecules can diffuse within the plane of a membrane.

When the transport vesicle shown below fuse with the plasma membrane, which monolayer will face the cell cytosol?

The organge monolayer will face the cytosol(outside)

In 1925, scientists exploring how lipids are arranged within cell membranes performed a key experiment using red blood cells. Using benzene, they extracted the lipids from a purified sample of red blood cells. Because these cells have no nucleus and no internal membranes, any lipids they obtained were guaranteed to come from the plasma membrane alone.The extracted lipids were floated on the surface of a trough filled with water, where they formed a thin film. Using a movable barrier, the researchers then pushed the lipids together until the lipids formed a continuous sheet only one molecule thick.The researchers then made an observation that led them to conclude that the plasma membrane is a lipid bilayer. Which of the following would have allowed the scientists to come to this conclusion?

The researchers found that the extracted lipids occupied twice the area of the original, intact cells. Additional experiments showed that lipids can spontaneously form bilayers when mixed with water. Together, theses observations suggest that in an intact cell membrane. the lipid molecules double up to form a bilayer-an arrangement that has a profound influence on cell biology. The extracted lipids covered twice the surface area of the intact red blood cells.

Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell.

by activating a scramblase and inactivating a flippase in the plasma membrane

Intracellular condensates are non-membrane bound biochemical subcompartments that form due to phase separation among networks of weakly interacting molecules. Sabari et al., 2018, proposed that the transcriptional coactivator BRD4 helps form intracellular condensates containing other transcriptional proteins. A prediction of this proposal is that BRD4 should behave as a liquid within the condensate with rapid movement. Which procedure could be used to analyze movement of BRD2 in living cells?

fluorescence recovery after photobleaching (FRAP) Fluorescence recovery after photobleaching is a technique used to track the diffusion rate of fluorescently tagged molecules. The quicker the recovery of fluorescence in the bleached area, the faster the diffusion rate of the tagged molecules.