Bsc1010c ch7

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar

All cells have voltages across their membranes. This voltage is called a(n) __________ and is often maintained by __________.

Membrane potential; electrogenic pumps

Which of the following molecules are most abundant in the plasma membrane?

Phospholipids

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct?

Phospholipids form a selectively permeable structure

Which of the following structural arrangements of the components in biological membranes facilitates the cell membrane's property of selective permeability?

Proteins embedded in two layers of phospholipids

How does the "fluid mosaic model" describe the structure of the plasma membrane?

Proteins in the membrane contribute to the mosaic quality of the membrane while the lateral and rotational movements of phospholipids contribute to its fluidity.

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids

The sodium-potassium pump __________.

Transport sodium ions out of the cell and transports potassium ions into the cell

Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration outside the cell. What type of transport is used to move lactose into the cell? a) Active transport b) Simple diffusion c) Facilitated diffusion d) Osmosis

a) Active transport (Under these conditions, lactose moves against its concentration gradient, so its transport will require energy.)

Which of the following substances would be most likely to pass through the plasma membrane without the help of a transport protein?

A nonpolar molecules, such as a hydrocarbon

If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?

Both cells with these water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall

Which of the following molecules is most likely to passively diffuse across the plasma membrane?

Carbon dioxide

What function do carbohydrates fulfill in the plasma membrane?

Cell to cell recognition

In facilitated diffusion, __________ proteins provide openings in the plasma membrane for substances to flow through without changing structure, and __________ proteins allow passage of substances through the plasma membrane after undergoing a subtle change in shape.

Channel; carrier

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic

Which of the following statements about diffusion is true?

It is a passive process

The internal solute concentration of a plant cell is about 0.8M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?

1.0M

Which of the following plant cells would exhibit the most turgor pressure?

A cell placed in a hypotonic solution

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Ampithatic Nature

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane?

Exocytosis and smooth and rough ER

Which of these statements describes some aspect of facilitated diffusion?

Facilitated diffusion of solutes May occur through channel or transport proteins in the membrane

True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell for every two potassium ions pumped out of the cell.

False

What distinguishes facilitated diffusion from simple diffusion?

Membrane proteins help move molecules across the membrane.

A cell is placed into a solution and the cell shrinks. Which of the following is true regarding the solution?

The solution is hypertonic

Which of the following is correct regarding integral proteins?

These proteins exhibit both hydrophilic and hydrophobic properties

Because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). Together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. Consider the plasma membrane of an animal cell that contains a sodium-potassium pump as well as two non-gated (always open) ion channels: a Na+ channel and a K+ channel. The effect of the sodium-potassium pump on the concentrations of Na+ and K+ as well as the distribution of charge across the plasma membrane is indicated in the figure below. A diagram of a plasma membrane containing a sodium-potassium pump, a non-gated Na+ channel, and a non-gated K+ channel. Outside of the cell, Na+ concentration is high, K+ concentration is low, and the charge is positive. Inside of the cell, Na+ concentration is low, K+ concentration is high, and the charge is negative. The sodium-potassium pump is moving three Na+ ions outside and two K+ ions inside. Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.

-The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. -The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. -The electrochemical gradient is larger for Na+ than for K+.

Which of the following would be least likely to diffuse through a plasma membrane without the help of a transport protein?

A large polar molecule

How does cholesterol affect membrane fluidity?

At body temperature, it makes the membrane less fluid

ells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B; cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.

B;The diffusion gradient in cell B is steeper

Active transport by the sodium-potassium pump follows this cycle.

The number one, corresponding to step one in a diagram below the text. Three Na+ ions from the cytosol bind to the pump. The number two, corresponding to step two in the diagram below the text. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. The number three, corresponding to step three in the diagram below the text. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. The number four, corresponding to step four in the diagram below the text. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. The number five, corresponding to step five in the diagram below the text. Release of the phosphate group causes another conformational change in the pump. The number six, corresponding to step six in the diagram below the text. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.

The plasma membrane exhibits selective permeability. This means that __________.

The plasma membrane allows some substances to flow through it more easily than other substances

Six major functions of membrane proteins

Transport, enzymatic activity, signal transduction, cell cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix

Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel? a) The charge on the other side of the membrane is generally the opposite of the ion's charge. b) There is a higher concentration of ions on the side of the membrane toward which the ion diffuses. c) For every ion that diffuses through the membrane, a different ion diffuses in the opposite direction. d) The cell expends energy as the ion passes through the membrane.

a) The charge on the other side of the membrane is generally the opposite of the ion's charge. (Ions tend to move toward regions of unlike charge.)

Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration? a) Transporter b) No protein is necessary. c) Pump d) Ion channel

a) Transporter (The GLUT-1 transporter assists the diffusion of glucose through the membrane.)