Bio 121 Unit 2: Membranes

Q1: 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 interactions

How Sodium-Potassium Pump Works?

1. It is an active transport mechanism that is driven by the breakdown of ATP and works through a series of conformational changes in a transmembrane protein; 2. 3 Sodium ions bind to the protein channel and an ATP provides the energy to change the shape of the channel that in turn drives the ions through the channel; 3. This binding again causes a change in the shape of the protein channel and this conformational change releases the phosphate group on the cytoplasm side; 4. This release allows the channel to revert to its original shape and as a result, the potassium ions are released inside of the cell; 5. In its original shape the channel has a high affinity for sodium ions and when these ions bind again, they initiate another cycle;

Ratio Na+/K+?

3 Na+ are exported for every 2 K+ imported into cell;

Q12: 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

What generates ion electrochemical gradients?

ATP-driven ion pumps generate ion electrochemical gradients;

Na+/K+-ATPase

Actively transports Na+ and K+ against their gradients using the energy from ATP hydrolysis;

Transporters

Also known as carriers;Conformational change transports solute across membrane;

Q18: 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.

Q35: ---------- bind two or more ions or molecules and transport them in opposite directions across a membrane.

Antiporters

Q45: 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

What is the important characteristic of the sodium-potassium pump?

Both Sodium and Potassium ions are moving from areas of low concentration to areas of high concentration, i.e. each ion is moving against its concentration gradient; This constant movement can only be achieved by the constant expenditure of ATP energy. Na - Out, K - in

Q23: Which molecule would you predict moves through a lipid bilayer most rapidly? C6H12O6 CH3OH C2H5OH C4H10 NH2SO2CH3

C4H10

Q32: What process best characterizes Ca2+ movement from the cytosol (low Ca2+ concentration) into the endoplasmic reticulum (high Ca2+ concentration)?

Calcium movement involves active transport.

Q22: Which molecule passes through a lipid bilayer most readily? carbon dioxide glucose K+ arginine RNA

Carbon dioxide

Q19: Glycosylated proteins and lipids within the plasma membrane are important for

Cell recognition and protection.

Q15: 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.

Channels

Form an open passageway for thedirect diffusion of ions or molecules across the membrane; When a channel is open, a solute directly diffuses through the channel to reach the other side of the membrane. Most are gated; Example: Aquaporins

Q39: 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;

What is used to transport large molecules such as proteins and polysaccharides?

Exocytosis and Endocytosis

Q37: The release of the protein insulin from pancreatic cells occurs by

Exocytosis.

Electrogenic pump

Exports one net positive (+) charge

Q28: 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.

Q2: Cellular membranes are

Fluid

Q17: Cellular membranes are mosaic and

Fluid.

Q6: 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 bilayer

Q24: 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.

Antiporter

Ions move in opposite directions;

Q27: Passive diffusion

Is a spontaneous process

Q7: 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

Q33: Acetylcholine binds this membrane protein, which subsequently opens to allow sodium to enter the cell. Acetylcholine exerts its effect on what type of transport protein?

Ligand-gated channel

Exocytosis

Material inside the cell packaged into vesicles and excreted into the extracellular medium;

Active transport

Movement of a solute across a membrane against its gradient from a region of low concentration to higher concentration; Energetically unfavorable and requires the input of energy;

Q40: 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 rigidifies the plasma membrane There is an error in the experimental procedure because this result is impossible Mysteriase is bound to the cytoskeletal filament Mouse cells are less fluid than human cells Mysteriase is a flippase enzyme that enhances lipid flip-flop rather than lipid lateral movement

Mysteriase is bound to the cytoskeletal filament;

Q41: 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

What are the principal molecules that Transporters transport?

Organic molecules, such as sugars, amino acids, and nucleotides;

Q29: The pressure required to stop water from moving across the membrane by osmosis is called

Osmotic pressure.

Q42: How does a macrophage (immune cell) consume a bacteria?

Phagocytosis

Q3: What is the major lipid found in membranes?

Phospholipids

Q13: What are the two major components of cell membranes?

Phospholipids and proteins;

Q10: 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

Q9: The membrane component(s) primarily responsible for the structure and function of plasma membranes is/are

Phospholipids.

Endocytosis

Plasma membrane invaginates (folds inward) to form a vesicle that brings substances into the cell

Q26: 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.

Q30: 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.

Tool for Primary Active Transport?

Primary active transport uses a pump; Directly uses energy to transport solute;

What are the 3 types of endocytosis?

Receptor-mediated endocytosis Pinocytosis Phagocytosis

Q38: 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;

Q34: 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

Uniporter

Single molecule or ion; A single solute moves in one direction.

Q25: 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.

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.

Q11: 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

Q31: The movement of sucrose and H+ into the cell by the same membrane protein reflects the actions of what type of transporter?

Symporter

Q8: 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.

Q14: 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.

Q21: Placing celery sticks in fresh water will make them more turgid and harder. This is because

The celery is hypertonic to fresh water.

Q44: 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;

Q5: 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;

Q16: What process(es) are required for phospholipids to flip-flop across the lipid bilayer?

The process requires energy and the flippase enzyme.

Q43: 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

Q20: Which membrane component is most important for allowing large, charged molecules to pass through the membrane?

Transmembrane proteins

Transport Protein

Transport proteins are transmembrane proteins that provide a passageway for the movement of ions and hydrophilic molecules across membranes;

What are the two classes of Transport Proteins?

Two classes based on type of movement 1. Channels 2. Transporters

Antiporter

Two or more ions or molecules transported in opposite directions; Two or more ions or molecules transported in opposite directions;

Symporter or cotransporter

Two or more ions or molecules transported in same direction; Two solutes move in the same direction.

3 Transporter Types

Uniporter; Symporter or cotransporter; Antiporter;

Tool for Secondary Active Transport?

Uses a pre-existing gradient to drive transport;

Q4: The plasma membrane...

is composed of an extracellular and intracellular layer of phospholipids.

Q36: The plasma membrane Na+/K+-ATPase pump

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