Chapter 5 Test File

A protein that forms an ion channel through a membrane is most likely to be a transmembrane protein because transmembrane proteins span the entire phospholipid bilayer of the membrane. This allows them to create a channel or pore through which ions can pass, facilitating the movement of ions across the membrane. Peripheral proteins are located on the surface of the membrane and do not span the entire bilayer, making them less likely to form an ion channel. Phospholipids are a type of lipid molecule that make up the bilayer itself, and enzymes are proteins that catalyze chemical reactions, neither of which are directly involved in forming ion channels.

In biological membranes, the phospholipids are arranged in a bilayer, with the fatty acids pointing toward each other. This arrangement is due to the polar nature of the phospholipids, which have a hydrophilic (water-loving) head and a hydrophobic (water-repelling) tail. The hydrophilic heads of the phospholipids face outward towards the aqueous environment, while the hydrophobic tails face inward, creating a barrier between the interior and exterior of the cell. This bilayer arrangement provides stability and allows for the selective permeability of the membrane.

Biological membranes are composed of lipids, which form a barrier to the movement of hydrophilic (water-loving) materials across the membrane. Lipids are hydrophobic (water-repelling) in nature, and their arrangement in the membrane creates a hydrophobic interior that prevents the passage of hydrophilic substances. Integral membrane proteins are embedded within the lipid bilayer and play various roles, but they do not form the primary barrier. Carbohydrates, nucleic acids, and peripheral membrane proteins are not primarily responsible for forming a barrier to the movement of hydrophilic materials across the membrane.

Peripheral proteins are loosely attached to the surface of the cell membrane and can be easily removed in a laboratory experiment. They are not embedded within the lipid bilayer like integral proteins or transmembrane proteins. Channel proteins and gated channels are types of integral proteins, so they would not be easily removed. Therefore, the most likely answer is c. Peripheral proteins.

The correct answer is a. many proteins can move around within the bilayer. This is because the membrane proteins are not fixed in place, but rather they have the ability to move within the lipid bilayer of the cell membrane. This movement allows for the proteins from the mouse cell and the human cell to become uniformly distributed over the surface of the hybrid cell when they are fused together. This phenomenon is due to the fluidity of the lipid bilayer, which allows for the proteins to freely move and mix with each other.

Houseplants that are adapted to indoor temperatures may die when accidentally left outdoors in the cold because their membranes lack adequate fluidity. Membranes are made up of lipids, which can become rigid and less fluid in cold temperatures. This can disrupt the normal functioning of the membranes, affecting various cellular processes such as nutrient uptake, water transport, and waste removal. As a result, the houseplant may not be able to properly maintain its physiological functions and eventually die.

The hydrophilic regions of a membrane protein are most likely to be found exposed on the surface of the membrane because hydrophilic regions are attracted to water and therefore will be oriented towards the aqueous environment on either side of the membrane. This allows the hydrophilic regions to interact with water molecules and participate in various cellular processes such as transport of ions and molecules across the membrane.

Cholesterol molecules are known to alter the fluidity of the membrane. They do this by inserting themselves between the phospholipids in the membrane, which reduces the movement of the phospholipids and makes the membrane less fluid. This helps to maintain the integrity and stability of the membrane, preventing it from becoming too rigid or too fluid. Cholesterol also plays a role in regulating the fluidity of the membrane in response to changes in temperature, ensuring that the membrane remains functional under different conditions.

The capacity of lipids to associate and maintain a bilayer organization is a characteristic of plasma membranes that helps them fuse during vesicle formation and phagocytosis. This is because the lipid bilayer structure allows for the fusion of membranes, as the lipids can easily associate and reorganize. This characteristic allows for the formation of vesicles and the engulfment of particles during phagocytosis. The ratio of protein to phospholipid molecules, the fatty acid chain length and degree of saturation, and the asymmetrical distribution of membrane proteins are not directly related to the fusion of plasma membranes during vesicle formation and phagocytosis.

The correct answer is c. hydrophobic. The question states that the protein crosses the plasma membrane, which is composed of a lipid bilayer. Hydrophobic amino acid side chains are nonpolar and repel water, making them more likely to interact with the hydrophobic interior of the membrane. This allows the protein to anchor itself in the membrane and span across it. Charged and hydrophilic amino acid side chains would be more likely to interact with the aqueous environment inside or outside the cell, respectively. Carbohydrates and lipids are not mentioned in the context of the question.

When a membrane is prepared by freeze-fracture and examined under the electron microscope, the exposed interior of the membrane bilayer appears to be covered with bumps. These bumps are actually integral membrane proteins. This is because integral membrane proteins are embedded within the lipid bilayer of the membrane, and when the membrane is fractured, these proteins are exposed on the fractured surface, appearing as bumps under the electron microscope. Ice crystals, platinum, organelles, and vesicles are not typically observed in this context.

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Cytoplasmic plaques are not specialized cell junctions. Gap junctions are specialized cell junctions that allow for direct communication between adjacent cells, while tight junctions are specialized cell junctions that create a barrier between cells to prevent the movement of molecules between them. Desmosomes are specialized cell junctions that provide mechanical strength to tissues. Cytoplasmic plaques, on the other hand, are structures within desmosomes that anchor intermediate filaments to the cell membrane, but they are not considered specialized cell junctions themselves. Therefore, the correct answer is d. Cytoplasmic plaques.

The correct answer is b. on the outer side of the membrane, protruding into the environment. The plasma membrane of animals contains carbohydrates on the outer side of the membrane, which helps in cell recognition and cell signaling. These carbohydrates are attached to proteins and lipids on the outer surface of the membrane, forming glycoproteins and glycolipids. This outer layer of carbohydrates is involved in various cellular processes, such as immune responses and cell-cell interactions.

The plasma membranes of winter wheat are able to remain fluid when it is extremely cold by replacing saturated fatty acids with unsaturated fatty acids. Unsaturated fatty acids have double bonds in their carbon chains, which introduces kinks and prevents the fatty acids from packing tightly together. This increases the fluidity of the membrane, allowing it to remain functional even at low temperatures.

The correct pathway for the synthesis and secretion of insulin involves the protein being synthesized in the rough endoplasmic reticulum (ER), then transported to the Golgi apparatus for further processing. From the Golgi apparatus, the insulin is packaged into vesicles, which then fuse with the plasma membrane to release the insulin outside the cell. Therefore, option a. Rough ER; Golgi apparatus; vesicle; plasma membrane is the correct answer.

The correct answer is e. The two membranes differ in their lipid composition. This means that the proteins of the plasma membrane and the proteins of the inner mitochondrial membrane have different types or amounts of lipids associated with them. This difference in lipid composition likely contributes to the different functions and properties of these two membranes.

Protein movement within a membrane may be restricted by the cytoskeleton and lipid rafts. The cytoskeleton is a network of protein filaments that provides structural support to the cell and can act as a barrier to protein movement. Lipid rafts are specialized regions of the membrane that contain high concentrations of cholesterol and sphingolipids, and they can also restrict protein movement by creating a more rigid environment. Together, the cytoskeleton and lipid rafts play a role in maintaining the organization and integrity of the cell membrane.

Glycolipids function as recognition signals for interactions between cells. They are composed of a carbohydrate chain attached to a lipid molecule. These molecules are located on the cell surface and play a crucial role in cell-cell recognition and communication. Glycolipids are involved in various cellular processes, including immune responses, cell adhesion, and cell signaling. They can act as receptors for signaling molecules and facilitate cell-cell adhesion by binding to specific proteins on neighboring cells. Therefore, glycolipids are essential for mediating interactions between cells.

Peripheral membrane proteins are proteins that are not embedded within the lipid bilayer but are attached to the membrane surface. They have hydrophilic regions that interact with the aqueous environment on either side of the membrane. These hydrophilic regions can also interact with similar regions of integral membrane proteins, which are proteins that are embedded within the lipid bilayer. This interaction allows peripheral membrane proteins to perform various functions, such as facilitating the transport of molecules across the membrane or transmitting signals between the cell's interior and exterior. Therefore, the correct answer is e. polar regions that interact with similar regions of integral membrane proteins.

The functional roles for different proteins found in membranes include allowing movement of molecules that would otherwise be excluded by the lipid components of the membrane, transferring signals from outside the cell to inside the cell, maintaining the shape of the cell, and facilitating the transport of macromolecules across the membrane. However, stabilizing the lipid bilayer is not a function of proteins in the membrane. Proteins can interact with the lipid bilayer, but their primary function is not to stabilize it.

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