Question 1

Phosphoglycerides

Accepted Answer

Phosphoglycerides are derivatives of phosphatidic acid, which contains both a glycerol backbone and a phosphate group. They are a type of phospholipid that make up the cell membrane of all living organisms. The other choices are incorrect: A) phosphoglycerides do not always contain a nitrogen base, as they can vary in their head group composition. C) phosphoglycerides are not derivatives of terpenes, which are a different class of lipids. D) phosphoglycerides are saponifiable, meaning they can be hydrolyzed by alkalis to form glycerol and fatty acids. E) phosphoglycerides usually contain a phosphate group as a part of their structure.

Question 2

Simple diffusion of a substance across a biological membrane

Accepted Answer

Simple diffusion occurs down a concentration gradient and is a passive process that is directly proportional to the concentration difference across the membrane, making it a linear function. Saturation kinetics occur in facilitated diffusion or active transport where a limited number of carrier proteins are available. Simple diffusion does not involve membrane carriers. Similarly, it is not affected by the presence of a compound of similar chemical structure, and it is not dependent on the concentration of other solutes in the system.

Question 3

A typical transmembrane domain in a protein is

Accepted Answer

A transmembrane domain typically consists of an alpha helix containing a mixture of nonpolar amino acids that can interact with the hydrophobic lipid bilayer of the membrane. The aromatic amino acids may be present in the helix, but they are not typically the predominant amino acids in a transmembrane domain. Beta sheets are not commonly found in transmembrane domains.

Question 4

A structural feature common to all membrane forming lipids is

Accepted Answer

All membrane forming lipids are amphipathic, meaning that they have both hydrophobic and hydrophilic regions. This is necessary for the formation of a lipid bilayer, which is essential for the structure and function of cell membranes. The other options (A, B, C, and E) are not present in all membrane forming lipids.

Question 5

The organization of the glycerophospholipid phosphatidylserine in an aqueous environment is a

Accepted Answer

Phosphatidylserine, like other glycerophospholipids, organizes into a bilayer in an aqueous environment, with the hydrophobic fatty acyl residues sequestered from water and the hydrophilic head groups, including serine, exposed to water. This arrangement is critical for the structure of cell membranes.

Question 6

All of the following enter or leave mitochondria via a specific transport protein EXCEPT

Accepted Answer

Oxygen does not enter or leave mitochondria via a specific transport protein as it can diffuse across the mitochondrial membrane. The other molecules listed (ATP, inorganic phosphate, pyruvate, and malate) require specific transport proteins for their transport into or out of the mitochondria.

Question 7

The protein that is defective in cystic fibrosis normally functions as

Accepted Answer

The protein that is defective in cystic fibrosis is called cystic fibrosis transmembrane conductance regulator (CFTR) which normally functions as a chloride transporter protein.

Question 8

Membranes will have their greatest fluidity when which one of the following is present in the phospholipids?

Accepted Answer

Arachidonic acid is a polyunsaturated fatty acid, which increases membrane fluidity due to its multiple double bonds that prevent tight packing of the phospholipids.

Question 9

In treating a patient with congestive heart failure, you have prescribed digoxin (a cardiac glycoside) to strengthen the heart's output and maintain a regular rate. The target of this drug is the

Accepted Answer

Digoxin primarily targets the Na+/K+ - ATPase pump, inhibiting it. This leads to an increase in intracellular sodium, which in turn affects the calcium exchange, increasing intracellular calcium levels. The increased calcium enhances cardiac muscle contractility, which is beneficial in treating congestive heart failure.

Question 10

All of the following statements about a facilitated diffusion transport system are correct EXCEPT

Accepted Answer

Facilitated diffusion is not inherently vectorial or one-way; it allows for the movement of molecules across membranes down their concentration gradient in either direction, unlike active transport systems that move substances from one side of the membrane to the other in a specific direction.

Question 11

Phospholipids have the property of detergency. This is due primarily to

Accepted Answer

The amphipathic nature of phospholipids, with a polar head group and a hydrophobic tail, allows them to interact with both water and oil. This property enables them to act as detergents, able to both dissolve in and remove substances from surfaces. The polar head group contributes to its solubility in water, while the hydrophobic tail interacts with oily surfaces.

Question 12

Each of the following lipid types is a membrane constituent EXCEPT which one?

Accepted Answer

Triglycerides are not typically found in cell membranes as they are more commonly used for energy storage. Sphingolipids, phospholipids, gangliosides, and cholesterol are all important components of cell membranes.

Question 13

Which of the following is most likely to cross a membrane by a non-mediated diffusion process?

Accepted Answer

Non-mediated diffusion, also known as passive diffusion, occurs when small, uncharged molecules such as gases (e.g. CO2), lipid-soluble molecules (e.g. ethanol), and water molecules can pass through a membrane without the need for a transport protein. Glucose, sodium ions, ADP, and ATP are all charged or larger molecules that require transport proteins to pass through the membrane.

Question 14

Which statement is NOT characteristic of an active transport system for L-alanine in animal cells?

Accepted Answer

Active transport systems are specific for the molecules they transport. The statement that the system transports D- and L-alanine with equal facility is incorrect because active transport systems typically exhibit stereospecificity, meaning they would preferentially transport one isomer (e.g., L-alanine) over the other (D-alanine).

Question 15

All of the following are generally accepted as features of the fluid-mosaic model of membrane structure EXCEPT

Accepted Answer

The fluid-mosaic model of membrane structure includes rapid lateral diffusion of lipids and slow lateral diffusion of integral and peripheral proteins, asymmetrical arrangement of lipids, and infrequent transverse movement of lipids. However, it does not include rapid diffusion of inorganic ions across the lipid bilayer.

Question 16

Differences in bilayer fluidity among human cell membranes are due to

Accepted Answer

Cholesterol can have a major impact on membrane fluidity as it intercalates between phospholipids and affects their packing. Higher levels of cholesterol in the membrane can decrease fluidity, whereas lower levels can increase fluidity. Therefore, the ratio of cholesterol to phospholipids can largely influence the fluidity of the membrane.

Question 17

The formation in humans of specific membrane microdomains depends on all of the following EXCEPT

Accepted Answer

Temperature and pressure can affect the physical properties of lipids and proteins, which can in turn influence the formation of membrane microdomains. Therefore, all of the other options are factors that do contribute to the formation of specific membrane microdomains.

Question 18

The mechanism of action of many anesthetics is now thought to involve a

Accepted Answer

Many anesthetics are known to interact with the lipid bilayer of cell membranes and alter their structure and properties, leading to changes in membrane fluidity and organization. This has been shown to affect the function of membrane-bound proteins, such as ion channels and receptors, which are critical for the propagation of nerve impulses and other cellular processes. Therefore, option A is the best choice. Options B, C, and D are not supported by the current understanding of the mechanism of action of anesthetics.

Question 19

Which phospholipid would migrate closest to the plus (+) electrode in an electrophoresis cell at pH 7?

Accepted Answer

The migration of a phospholipid in an electrophoresis cell is influenced by its charge at a given pH. At pH 7, most phospholipids have a net neutrality, except for phosphatidylserine which carries a negative charge due to its phosphate group. Therefore, it would migrate closest to the plus (+) electrode.

Question 20

The asymmetry associated with biological membranes refers to the

Accepted Answer

The asymmetry of biological membranes refers to the differences in protein and lipid composition between the outer and inner leaflets of the membrane bilayer. Specifically, the outer leaflet often contains more glycolipids and glycoproteins, while the inner leaflet contains more phosphatidylserine and phosphatidylinositol. This asymmetry is critical for proper membrane function, as it affects important processes such as cell signaling and membrane trafficking.

Quiz 12: Biological Membranes: Structure and Membrane Transport