Bio 5

the movement of sucrose and H+ into the cell by the same membrane protein reflects the actions of what type of transporter?

symporter.

Placing celery sticks in fresh water will make them more turgid and harder. This is because

the celery is hypertonic to fresh water.

When phospholipids are mixed together in an aqueous environment, a membrane bilayer will form spontaneously. In what type of environment would a phospholipid bilayer not form spontaneously?

A hydrophobic solvent

How might a plant cell compensate for the excessive membrane fluidity that occurs during prolonged exposures to elevated temperature?

Alter the lipid composition to have longer fatty acyl tails and fewer double bonds.

__ bind two or more ions or molecules and transport them in opposite directions across a membrane.

Antiporters

Imagine that a cell can be treated with a drug that prevents proteins from undergoing large conformational changes. Which transport proteins would be unaffected by this drug treatment?

Aquaporin

Which molecule would you predict moves through a lipid bilayer most rapidly?

C4H10

What process best characterizes Ca2+ movement from the cytosol (low Ca2+ concentration) into the endoplasmic reticulum (high Ca2+ concentration)?

Calcium movement involves active transport.

A protein is tightly associated with the plasma membrane but it can be isolated by treating the membrane with a strong detergent. What type of membrane protein is this?

Either an integral or a peripheral membrane protein

Freeze fracture electron microscopy allows one to observe the two-dimensional cross section of membrane proteins.

False

Osmosis describes the movement of water from an area of high to low solute concentration.

False

Plant cell membranes contain cholesterol.

False

The Na+/K+-ATPase pump is a ligand-gated ion channel.

False

A researcher is studying the integral membrane protein "mysteriase" and chooses to perform an experiment similar to that performed by Frye and Edidin. The researcher fuses a mouse cell expressing mysteriase with a human cell. The fused cell is incubated at 37°C prior to being cooled to 0°C and labeled with a fluorescent antibody against mysteriase. When observed with a fluorescent microscope, mysteriase is observed to remain on one side of the fused cell. What is the most likely explanation for this surprising observation?

Mysteriase is bound to the cytoskeletal filament

Na+ ion concentrations are higher outside the cell than inside the cell. What type of transport system is required to move Na+ ions in and out of the cell?

Na+ moves into the cell by facilitated diffusion and out of the cell by active transport

An artificial membrane vesicle is mixed with several peripheral membrane proteins and analyzed by freeze-fracture electron microscopy. What will be seen in the resulting image?

No bumps will be visible in either face

If a cell suddenly loses the ability to activate fatty acids by the attachment of a CoA molecule, what will be the most significant impact on the cell membrane?

Phospholipids will no longer be synthesized in the ER

Two "magic" solutions are sold by a research supply company. "Magic Solution A" promises to extract all proteins, including integral membrane proteins, from the plasma membrane. "Magic Solution B" promises to simply extract all peripherally associated membrane proteins. What is the likely composition of "Magic Solution A" and "Magic Solution B"?

Solution A" is a membrane solubilizing detergent, "Solution B" is a high salt buffer that disrupts hydrogen bonds and ionic interaction

A scientist produces an artificial membrane from phospholipids and notices that oxygen, but not glucose, readily moves through the membrane. What might account for the inability of glucose to move through the artificial membrane?

The artificial membrane lacked a protein needed for glucose transport.

Cell surface molecules are labeled with a fluorescent tag and then a portion of them are bleached with a laser beam. What would one observe after the cell is incubated for a few minutes?

The bleached molecules would diffuse laterally through the membrane and intermix with unbleached molecules.

A researcher is studying a culture of eukaryotic cells that shows an abnormal pattern of surface glycosylation. The researcher determines that these cells have normal levels of glycolipids and integral membrane proteins with O-linked glycosylation. The researcher discovers that there are no N-linked glycosylated proteins on the cell surface and measures unusually high levels of glycosylated dolichol in the ER membrane. What is a reasonable hypothesis to explain this observation?

The cell has a defective oligosaccharide transferase

What would be an expected feature of a plasma membrane that had no integral membrane proteins?

The membrane would be unable to transport sodium ions

Animal cells are permeable to water and urea but NOT to sucrose. Initially, the inside of a cell contains 1 M sucrose and 1 M urea and the outside 2 M sucrose and 1 M urea. After the system reaches equilibrium, what changes are observed?

The molarity of sucrose would be similar inside and outside the cell and water would move out of the cell causing the cell to shrivel.

What process(es) are required for phospholipids to flip-flop across the lipid bilayer?

The process requires energy and the flippase enzyme

A dysfunctional cell lacks a signal peptidase and is unable to cleave the ER signal sequence from proteins translated in the ER. What will be the effect on the cell's proteins?

There will be a common signal sequence at the N-terminus of all integral membrane proteins in the plasma membrane

Which molecule passes through a lipid bilayer most readily?

carbon dioxide

Glycosylated proteins and lipids within the plasma membrane are important for

cell recognition and protection.

In order to study a cell at lower temperatures, a researcher must artificially increase its membrane fluidity. What would be a reasonable strategy for increasing plasma membrane fluidity at low temperatures?

decrease the length of the phospholipid fatty acyl tail.

The release of the protein insulin from pancreatic cells occurs by

exocytosis

Following a meal, glucose must move from the gut lumen where there is a high glucose concentration into the intestinal cell where there is a relatively low level of glucose. This movement is called

facilitated diffusion.

Cellular membranes are mosaic and

fluid

Cellular membranes are

fluid.

Scientists unearth a Wooly Mammoth from the Siberian Ice Sheath and discover that a eukaryotic "amoeba"-like cell is still alive. Which component of the cell membrane might contribute to maintaining the fluidity of plasma membranes under freezing conditions?

high levels of unsaturated fatty acyl tails within the lipid bilaye

Animal cells are permeable to water and urea but NOT to sucrose. The inside of a cell contains 1 M sucrose and 1 M urea and the outside 1 M sucrose and 2 M urea. The solution inside with respect to outside the cell is

hypotonic.

Passive diffusion

is a spontaneous process

The plasma membrane

is composed of an extracellular and intracellular layer of phospholipids.

The plasma membrane Na+/K+-ATPase pump

is used to generate sodium and potassium gradients across the membrane.

The pressure required to stop water from moving across the membrane by osmosis is called

osmotic pressure.

How does a macrophage (immune cell) consume a bacteria?

phagocytosis

What is the major lipid found in membranes?

phospholipids

The membrane component(s) primarily responsible for the structure and function of plasma membranes is/are

phospholipids.

Water diffuses through certain organs such as the kidneys and bladder much faster than would occur by passive diffusion through a lipid bilayer alone. What accounts for this more rapid rate of water transport in these organs?

presence of aquaporin channels for facilitated diffusion of water.

The process that most involves the selective uptake of a specific cargo molecule into the cell through receptor binding and aggregation is

receptor-mediated endocytosis.

Sodium concentrations are higher outside and glucose concentrations are higher inside the cell. Using the same membrane protein for Na+ and glucose transport, what is it called when a Na+ electrochemical gradient is used to drive glucose transport into the cell against its concentration gradient?

secondary active transport

What feature of the plasma membrane is primarily responsible for the selective uptake and export of ions and molecules from the cell?

the phospholipid lipid bilayer has a hydrophobic interior

Which membrane component is most important for allowing large, charged molecules to pass through the membrane?

transmembrane proteins

Diffusion is the movement of a molecule from an area of high to low concentration.

true

Movement of molecules down their concentration gradient can drive the movement of a different molecule against its concentration gradient.

true

The presence of integral proteins allows membranes to be selectively permeable to certain molecules.

true