Biology 1 (Biology 1610) CH.7 - "Membrane Structures and Functions."

Can water (H2O) directly cross a cellular plasma membrane?

No. Water is a polar molecule.

Do polar or non-polar molecules pass through a lipid-bilayer faster?

Non-polar molecules

Molecules have a type of energy called thermal energy, due to their constant motion. One result of this motion is ____________, the movement of particles of any substance so that they spread out into the available space.

diffusion

Small molecules cross membranes by ________________.

diffusion (Going from a high concentration to a low concentration.)

A _________________ remains fluid as temperature decreases until the phospholipids settle into a closely packed arrangement and the membrane solidifies, much as bacon grease forms lard when it cools.

membrane

The diffusion of free water across a selectively permeable membrane, whether artificial or cellular, is called ____________.

osmosis

What are the two types of transport proteins?

1. Channel proteins: provide corridors that allow specific molecules or ions to cross the membrane. 2. Carrier proteins: undergo a subtle change in shape that somehow translocates the solute-binding site across the membrane.

What mechanisms drive molecules across membranes?

1. Much of the traffic across cell membranes occurs by diffusion. When a substance is more concentrated on one side of a membrane than on the other, there is a tendency for it to diffuse across, down its concentration gradient. 2. Channel proteins, Carrier proteins (Passive transport) 3. Active transport

Phospholipids are made out of 3 basic units, what are they?

1. Phospho-group 2. A unit of glycerol 3. Fatty-acid

What are two forms of active transport?

1. Proton pump: creates an electrochemical gradient. 2. Cotransport (symporter):

A protein that spans a membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. A. Transport B. Enzymatic activity C. Signal transduction D. Cell-cell recognition

A

In a solution that is _____________, water will enter the cell faster than it leaves, and the cell will swell and lyse (burst) like an overfilled water balloon. A. Hypotonic B. Isotonic C. Hypertonic

A

Diffusion and facilitated diffusion such as channel proteins and carrier proteins are forms of: A. Active transport B. Passive transport C. Membrane transport D. Both A and B

B

What can occur following a gradient of concentration, going against the gradient of concentration, or where the concentration is the same on both sides. This process helps to create a gradient. A. Active transport B. Passive transport C. Membrane excitability D. Membrane transport

A

Which of the following factors would tend to increase membrane fluidity? A. a greater proportion of unsaturated phospholipids B. a greater proportion of saturated phospholipids C. a lower temperature D. a relatively high protein content in the membrane

A

Which of the following statements is true regarding potential energy? A. Potential energy is the energy possessed by matter due to its location or structure. B. Potential energy is the energy matter could have if it were in a different location or structure. C. Water acquires potential energy as it runs downhill. D. Matter has a natural tendency to acquire more potential energy until a maximum is reached.

A

Which of the following types of molecules are most likely to lack hydrophilic domains? A. cholesterol B. transmembrane proteins C. peripheral membrane proteins D. ion transport proteins

A

Which of the following best describes the structure of a biological membrane? A. two layers of phospholipids, with proteins either crossing the layers or on the surface of the layers B. two layers of phospholipids (with opposite orientations of the phospholipids in each layer), with each layer covered on the outside with proteins C. a fluid structure in which phospholipids and proteins move freely between sides of the membrane D. two layers of phospholipids, with proteins embedded between the two layers E. a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot

A (The membrane proteins can be found either embedded in, or attached to, the surface of the phospholipid bilayer.)

Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements. A. The diverse proteins found in and attached to membranes perform many important functions. B. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. C. The kinky tails of some proteins help keep the membrane fluid by preventing the component molecules from packing solidly together. D. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. E. Membranes include a mosaic, or mix, of carbohydrates embedded in a phospholipid bilayer.

A, B, D (Membranes consist of diverse proteins suspended in and attached to a phospholipid bilayer. Kinks in the unsaturated fatty acid tails of some phospholipids keep the membrane fluid, and a mosaic of proteins perform a variety of functions.)

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly: A. spread in a continuous layer over the inner and outer surfaces of the membrane. B. embedded in a lipid bilayer. C. randomly oriented in the membrane, with no fixed inside-outside polarity. D. confined to the hydrophobic interior of the membrane.

B

In what way do the membranes of a eukaryotic cell vary? A. Only certain membranes are constructed from amphipathic molecules. B. Certain proteins are unique to each membrane. C. Phospholipids are found only in certain membranes. D. Only certain membranes of the cell are selectively permeable.

B

In what way do the membranes of a eukaryotic cell vary? A. Phospholipids are found only in certain membranes. B. Certain proteins are unique to each membrane. C. Only certain membranes of the cell are selectively permeable. D. Only certain membranes are constructed from amphipathic molecules.

B

Specific ions and a variety of polar molecules can't move through cell membranes on their own. What assists them through the membrane? A. Nonpolar molecules B. transport proteins C. Lipid-bilayer D. None of the above

B

The diffusion of a substance across a biological membrane is called ____________ ______________ because it requires no energy. A. Active transport B. Passive transport C. Thermal Energy D. Direct diffusion

B

The most abundant lipids in most membranes are: A. Triglycerides B. Phospholipids C. Diglycerides D. Steroids

B

Water diffuses across the membrane of a red blood cell, but at the same rate in both directions. This is known as: A. Hypotonic B. Isotonic C. Hypertonic

B

What proteins are not embedded in the lipid bilayer at all; they are loosely bound to the surface of the membrane, often to exposed parts of integral proteins. A. Integral proteins B. Peripheral proteins C. Transmembrane proteins D. Both A and C

B

Which of the following statements best describes a characteristic feature of integral membrane proteins? A. They are hydrophilic. B. They are amphipathic, with at least one hydrophobic region. C. They are hydrophobic. D. They are localized to the interior surface of the membrane.

B

Which protein allows for the passage of water molecules through the membrane by making a hydrophilic channel: A. Integral proteins B. Aquaporin proteins C. Peripheral proteins D. Transmembrane proteins

B

Which of the following is least likely to be important in holding the components of a biological membrane together? A. hydrophobic interactions between the phospholipid tails and the surface of integral membrane proteins buried in the membrane B. covalent interactions between the phospholipid and protein components of the membrane C. hydrophobic interactions among the fatty acid tails of phospholipids on the same side of the membrane D. hydrophobic interactions among the fatty acid tails of phospholipids on opposite sides of the membrane E. polar interactions among the phospholipid head groups on the same surface of the membrane

B (This is not an important interaction because there are rarely covalent bonds between the phospholipids and integral membrane proteins.)

A phospholipid is an amphipathic molecule. What does this mean? A. Phospholipids are hydrophobic. B. Phospholipids are hydrophilic. C. Both A and B. D. Phospholipids have a double membrane.

C

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly: A. spread in a continuous layer over the inner and outer surfaces of the membrane. B. confined to the hydrophobic interior of the membrane. C. embedded in a lipid bilayer. D. randomly oriented in the membrane, with no fixed inside-outside polarity.

C

An increase in the salinity (saltiness) of a lake can kill the animals there; if the lake water becomes ______________ to the animals' cells, they might shrivel and die. A. hypotonic B. Isotonic C. Hypertonic

C

First, a small area of the plasma membrane sinks inward to form a pocket. Then, as the pocket deepens, it pinches in, forming a vesicle containing material that had been outside the cell. This process is known as: A. Facilitated diffusion B. Active transport C. Endocytosis D. Exocytosis

C

Many polar molecules and ions blocked by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane. This phenomenon is called: A. Diffusion B. Active transport C. Facilitated diffusion D. Polar diffusion

C

Which of the following processes includes all the others? A. osmosis B. diffusion of a solute across a membrane C. passive transport D. transport of an ion down its electrochemical gradient

C

Which of the following statements best describes the structure of a membrane based on the fluid mosaic model? A. The membrane is composed of a single layer of fluid phospholipids between two layers of hydrophilic proteins. B. The membrane is composed of a mosaic of fluid polysaccharides and amphipathic proteins. C. The membrane is composed of a fluid bilayer of phospholipids with embedded amphipathic proteins. D. The membrane is composed of a fluid bilayer of phospholipids between two layers of hydrophilic proteins.

C

In which environment does plasmolysis occur? A. Hypotonic environment B. Isotonic environment C. Hypertonic environment

C Plasmolysis: As the plant cell shrivels, its plasma membrane pulls away from the cell wall at multiple places.

Hydrophobic substances like salad oil are: A. nonpolar molecules that have an affinity for water because they contain many hydrogens that can form hydrogen bonds with water. B. polar molecules that have an affinity for water molecules because they contain many hydrogens that can form hydrogen bonds with water. C. nonpolar molecules that do not have an affinity for water molecules. D. polar molecules that do not have an affinity for water molecules.

C (Substances that are nonpolar due to their large number of nonpolar bonds do not have an affinity for water and are termed hydrophobic ("water-fearing"). Substances that contain polar bonds are hydrophilic ("water-loving") because they contain atoms with partial charges due to those polar bonds.)

_________________ helps to stabilize the structure of the plasma membrane.

Cholesterol

Which of the following statements about a typical plasma membrane is correct? A. The plasma membrane is a covalently linked network of phospholipids and proteins that controls the movement of solutes into and out of a cell. B. Phospholipids are the primary component that determines which solutes can cross the plasma membrane. C. The two sides of the plasma membrane have different lipid and protein composition. D. The hydrophilic interior of the membrane is composed primarily of the fatty acid tails of the phospholipids. E. Carbohydrates on the membrane surface are important in determining the overall bilayer structure.

C (because the membrane serves different functions on the cytoplasmic and exterior surfaces, the structure and composition of the surfaces must be different.)

A protein called ________ on the surface of immune cells helps the human immunodeficiency virus (HIV) infect these cells, leading to acquired immune deficiency syndrome (AIDS).

CD4

How do membrane phospholipids interact with water? A. The polar heads have no an affinity for water and the nonpolar tails have an affinity for water. B. They have hydrophilic tails that face outward and are exposed to water and hydrophobic heads that face the center of the membrane and are shielded from water. C. Phospholipids do not interact with water because they are lipids, and thus are completely hydrophobic. D. The polar heads interact with water; the nonpolar tails do not.

D

The cell secretes certain molecules by the fusion of vesicles with the plasma membrane; this process is called: A. Facilitated diffusion B. Active transport C. Endocytosis D. Exocytosis

D

Thus, __________________ can be thought of as a "fluidity buffer" for the membrane, resisting changes in membrane fluidity that can be caused by changes in temperature. A. Proteins B. Steroids C. Lipids D. Cholesterol

D

What proteins penetrate the hydrophobic interior of the lipid bilayer? A. Integral proteins B. Peripheral proteins C. Transmembrane proteins D. Both A and C

D

You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells? A. the nonpolar, hydrophobic nature of the drug molecule B. the concentration of the drug molecule that is transported in the blood C. the phospholipid composition of the target cells' plasma membrane D. the similarity of the drug molecule to other molecules that are transported into the target cells

D (If the target cells have transport proteins that specifically bind to certain molecules, they may bind with and transport a drug that is similar in structure.)

What does cholesterol do to a saturated or viscous membrane?

Makes the membrane more fluid. Ex: This is good when the environment or temperature gets colder and colder, because you want something that helps your membrane become fluid during cold temperatures.

A membrane exhibits ______________ ___________________; that is, it allows some substances to cross more easily than others.

selective permeability

Because of kinks in the tails where double bonds are located, __________________ hydrocarbon tails cannot pack together as closely as ________________ hydrocarbon tails, making the membrane more fluid.

unsaturated, saturated