Chapter 11, Quiz 11.2: Membrane Proteins chap 4

The tails of phospholipids are:

hydrophobic.

Bacteriorhodopsin is a membrane transport protein that uses sunlight to do what?

Pump H+ out of the cell to generate a H+ gradient across the plasma membrane

How does cholesterol in animal cell membranes affect the bilayer?

Cholesterol tends to stiffen the bilayer.

Which is NOT found in a cell membrane?

DNA

Which has a larger number of double bonds?

Vegetable oil

In a lipid bilayer, lipids rapidly diffuse:

within the plane of their own monolayer

What do carbohydrates attached to cell-surface proteins and lipids provide for a cell? (A) A distinctive identity in cell-cell recognition (B) A slimy coat that prevents cells from sticking to one another (C) Protection from mechanical and chemical damage (D) All of the above

(D) All of the above

Margarine is made from vegetable oils in which the hydrocarbon tails have had what treatment?

Removing the double bonds by adding hydrogen (which converts double bonds to single bonds)

In one second, a phospholipid molecule in an artificial bilayer may diffuse as far as what distance?

2 microns (the length of a large bacterial cell)

Which of these membrane-associated protein structures has never been found in a cell membrane? https://s3.amazonaws.com/RM_Images/20160117001214739_raw.jpg

5

How thick is the plasma membrane?

50 atoms

In a typical animal cell, approximately how much of the mass of the plasma membrane is constituted by proteins?

50%

Shown is a schematic diagram of a membrane phospholipid. Which segment could carry a positive charge? https://s3.amazonaws.com/RM_Images/20160117001209407_raw.jpg

A

Which FRAP curve would show a more rapid recovery of fluorescence: one obtained from a cell membrane that contained a large proportion of saturated fatty acids or one from a cell membrane with a large proportion of unsaturated fatty acids?

A membrane containing a larger proportion of unsaturated fatty acids would show a more rapid recovery in a FRAP study

Which is NOT an integral membrane protein?

A protein attached to the membrane by noncovalent interactions with other membrane proteins

The movement of an individual protein in a cell membrane can be followed using a technique called single-particle tracking. In the diagram of the red blood cell cortex shown in Figure 1, actin proteins would show which of the three types of movement in Figure 2? https://s3.amazonaws.com/RM_Images/20160117001225232_raw.jpg

C

Treatment of this membrane with a detergent like sodium dodecyl sulfate (SDS) would release which protein or proteins from the bilayer? https://s3.amazonaws.com/RM_Images/20160117001217723_raw.jpg

All of the proteins

Shown is a schematic diagram of a membrane phospholipid. Which segment will always carry a negative charge? https://s3.amazonaws.com/RM_Images/20160117001211078_raw.jpg

B

Treatment of this membrane with phospholipase C would release which protein or proteins from the bilayer? https://s3.amazonaws.com/RM_Images/20160122194232670_raw.jpg

B

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. How might a cell engineer this phospholipid redistribution?

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

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 here are three different proteins associated with the cell membrane. Treatment of this membrane with high salt would release which protein or proteins from the bilayer? https://s3.amazonaws.com/RM_Images/20160117001216210_raw.jpg

C

Which is NOT a mechanism for restricting the movement of proteins in the plasma membrane?

Coating proteins with carbohydrates

Human red blood cells contain no internal membranes other than the nuclear membrane.

False

The plasma membrane is NOT involved in:

DNA replication.

Double bonds in hydrocarbon tails have what effect on phospholipid tails and the rigidity of the lipid bilayer?

Double bonds decrease the ability of hydrocarbon tails to pack together, which makes the bilayer less stiff.

On what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located?

External (noncytosolic) side

All of the carbohydrates in the plasma membrane face the cell exterior, and the carbohydrates on internal cell membranes face the cytosol.

False

Which of the following is NOT a function of plasma membrane proteins?

Generate the energy required for lipids to diffuse through the membrane

Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains?

Hydrophobic

Which is NOT true of the molecule whose structural formula is shown? https://s3.amazonaws.com/RM_Images/20160117001212626_raw.jpg

It is found in the membranes of virtually all living cells.

Treating this membrane with a lectin would release which protein or proteins from the bilayer? https://s3.amazonaws.com/RM_Images/20160117001219226_raw.jpg

None of the proteins

Which is the most abundant phospholipid in animal cell membranes?

Phosphatidylcholine

Which statement about phospholipids and detergents is NOT true?

Phospholipids are amphipathic, whereas detergents are hydrophobic.

Which of the following will produce the most fluid lipid bilayer?

Phospholipids with tails of 18 carbon atoms and two double bonds

What type of enzyme moves randomly selected phospholipids from one monolayer of a lipid bilayer to the other?

Scramblase

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 can also be lipids. How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?

The FRAP curve for lipids would show very rapid recovery to initial levels of fluorescence.

Which portion of a membrane phospholipid faces the outside of the membrane?

The head

Why do phospholipids form bilayers in water?

The hydrophilic head is attracted to water while the hydrophobic tail shuns water.

When the transport vesicle shown here fuses with the plasma membrane, which monolayer will face the cell cytosol? https://s3.amazonaws.com/RM_Images/20160117001207674_raw.jpg

The orange monolayer

In a patch of animal cell membrane about 10 µm in area, which will be true?

There will be more lipids than proteins.

The oils found in plant seeds and the fats found in an animal's fat (or adipose) cells:

are hydrophobic.

The entire phospholipid molecule is:

amphipathic

The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called the:

cell cortex

Organisms that live in cold climates adapt to low temperatures by:

increasing the amounts of unsaturated fatty acids in their membranes to help keep their membranes fluid.

A functionally specialized region of a cell membrane, typically characterized by the presence of specific proteins, is called a:

membrane domain

When grown at higher temperatures, bacteria and yeast maintain an optimal membrane fluidity by:

producing membrane lipids with tails that are longer and contain fewer double bonds

In eukaryotic cells, new phospholipids are manufactured by enzymes bound to:

the cytosolic face of the endoplasmic reticulum.

Multipass transmembrane proteins can form pores across the lipid bilayer. The structure of one such channel is shown in the diagram. In this figure, the areas shown in red represent: https://s3.amazonaws.com/RM_Images/20160117001221000_raw.jpg

the hydrophilic side chains of the transmembrane α helices.

When a vesicle fuses with the plasma membrane, the monolayer that was facing the inside of the vesicle will face:

the outside of the cell.

In the α helices of transmembrane proteins, the hydrophobic side chains are facing:

the outside of the membrane-spanning helix.