Bio Test 2

Figure 1. Testosterone movement across the cellular membrane Testosterone is a small steroid hormone that is important in cell signaling. Which of the following indicates where testosterone enters a cell and why it is able to cross at that point?

1, because testosterone is nonpolar and can diffuse through the membrane.

Glycolipids

A lipid covalently attached to a carbohydrate

Amphipathic

A molecule that has both hydrophobic and hydrophilic regions

Selective permeability

A property of biological membranes that allows some substances to cross more easily than others

Peripheral proteins

A protein appendage loosely bound to the surface of a membrane and not embedded in the lipid bilayer.

Ion Channels

A protein channel in a cell membrane that allows passage of a specific ion down its concentration gradient

Gated Channels

A protein channel in a cell membrane that opens or closes in response to a particular stimulus

Glycoproteins

A protein covalently attached to a protein

Transport protein

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane

Aquaporin

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).

pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes

Phagocytosis

A type of endocytosis that involves large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.

A study was conducted to understand the factors controlling the rate at which molecules or ions travel across cell membranes. An artificial membrane was created that was composed of a phospholipid bilayer only. The speed at which various substances crossed this membrane was measured. Some substances can pass through an actual cell membrane much faster than they passed through the artificial membrane in this study. Which of the following statements best explains this finding?

Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane.

A magnesium sulfate solution taken orally can cause a net movement of water into the large intestine, which results from water molecules diffusing through aquaporins embedded in the cells of the intestinal lining. By which of the following mechanisms do the water molecules most likely move into the large intestine?

By passive transport from an area of low osmolarity to an area of high osmolarity

Aldosterone (a steroid hormone) is a small, nonpolar, hydrophobic molecule that enters a target cell by moving across the plasma membrane, down a concentration gradient. Based on the information presented, how does aldosterone most likely enter target cells?

By simple diffusion

The cell membrane is selectively permeable due to its structure. Thus, the internal environment of the cell is distinct from the external environment of the cell. One biologist hypothesizes that small nonpolar molecules readily pass through the membrane. Another biologist alternatively hypothesizes that these types of molecules require channel and transport proteins that are embedded in the membrane in order to move across the membrane. Which of the following data would best refute this alternative hypothesis?

CO2CO2 and N2N2 movement in and out of cells is unaffected when membrane protein activity is blocked.

Some cells, such as intestinal cells, exchange a lot of material with their surroundings. The surface-to-volume ratio of these cells affects the efficiency of material exchange. The table provides measurements of four different eukaryotic cells. Based on the data, which cell is likely to be most effective in the exchange of materials?

Cell 2

Compare and contrast active transport and cotransport

Cotransport and active transport are both forms of transportation within the cell. They both require energy. The electrochemical gradients set up by primary active transport store energy, which can be released as the ions move back down their gradients. Secondary active transport uses the energy stored in these gradients to move other substances against their own gradients.

Cholesterol is a naturally occurring substance that helps regulate the fluidity of a cell's plasma membrane. A cholesterol molecule can be represented as having a polar head and a nonpolar region, as shown in the figure. Which of the following models shows how cholesterol molecules most likely interact with the phospholipid bilayer of a cell's plasma membrane?

D

Two competing hypotheses exist regarding the cell membrane structure. One hypothesis states that membrane structure is static and membrane components throughout the bilayer are rigidly bound. Alternatively, the other hypothesis states that cell membranes are a fluid mosaic in which membrane components may drift within the bilayer around the surface of the cell. An experiment is set up in which membrane proteins of two different cells are fluorescently labeled with two different colors and then fused as shown in Figure 1. Figure 1. Model of initiation of cell fusion experiment Which of the following results, one hour after membrane fusion, best supports the alternative hypothesis that the cell membrane is a fluid mosaic?

D, membrane proteins mixed together.

A student is using dialysis bags to model the effects of changing solute concentrations on cells. The student places one dialysis bag that contains 25 mL of distilled water into each of two beakers that are filled with 200 mL of distilled water. (Figure 1). The membrane of each dialysis bag membrane contains pores that allow small solutes such as monoatomic ions to pass through but are too small for anything larger to pass. After 30 minutes, 5 mL of a concentrated solution of albumin (a medium-sized, water-soluble protein) is added to one of the two beakers. Nothing is added to the other beaker. After two more hours at room temperature, the mass of each bag is determined. There is no change in the mass of the dialysis bag in the beaker to which no albumin was added. Which of the graphs below best represents the predicted change in mass over time of the dialysis bag in the beaker to which albumin was added?

Graph B, dialysis weight goes down after albumin is added

Isotonic

Having the same solute concentration as another solution.

List 6 substances that need to move across a membrane

Hydrocarbons, carbon dioxide, oxygen, glucose, water, amino acids need to move across a membrane.

Hypertonic

In comparing two solutions, referring to the one with a greater solute concentration.

Researchers investigate the transport of a certain protein into cells by endocytosis. In an experiment, the researchers incubate the cells in the presence of the protein and measure the amount of the protein that is absorbed into the cells over a five-minute period. Based on their observations, what should the researchers do to further clarify how the availability of the protein outside the cells affects the rate of endocytosis of the protein?

Incubate the cells in the absence of the protein.

In an experiment, researchers compared the growth of two different plants, plant X and plant Y. The researchers maintained the plants under nearly identical conditions and observed that plant X grew faster than plant Y. The researchers also observed that the inner mitochondrial membranes of plant X had more folds than did those of plant Y. Which of the following conclusions about increasing the number of folds in the inner mitochondrial membrane is best supported by the results of the experiment?

It increases the surface area available for ATP production, which results in faster cell growth.

Flaccid

Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter.

List two molecules that move across a membrane by simple (not facilitated) diffusion.

Oxygen and carbon dioxide move across a membrane by simple diffusion.

The figure shows a representation of a protein embedded in a cell membrane. The numbers indicate different structural regions of the protein. Based on the figure, which of the following statements best describes the relationship between regions 1 and 2 of the protein?

Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane.

Intravenous (IV) therapy is used for fluid replacement in instances of dehydration in humans and other animals. One type of IV fluid is essentially a saltwater solution. To determine the best concentration for therapy in people, a team of students is researching the effects of solutions of different salt concentrations on red blood cells. The following observations were made from three different red blood cell samples viewed under a microscope. 0.3% Saline (Cells swell) 0.9% Saline (Cells unchanged) 1.5% Saline (Cells shrink) The team wants to extend the research project. What should the team of students do next to obtain data that are more conclusive?

Repeat the process with other salt concentrations.

Some membrane proteins help maintain the concentrations of ions inside a cell by transporting the ions across the cell's plasma membrane. Other membrane proteins form pores in the plasma membrane through which the ions can diffuse. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across a plasma membrane is presented in Figure 1. Figure 1. Section of a cell's plasma membrane, showing ion concentrations and membrane proteins Based on the model presented in Figure 1, which of the following changes will most likely result from a depletion of available ATP stores inside the cell?

The Na+ concentration inside the cell will increase.

Endocytosis

The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.

Cotransport

The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient

Electrochemical gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

Osmosis

The diffusion of water across a selectively permeable membrane.

Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, H+ ions are transported into the lysosome from the cytosol. This significantly lowers the pH of the lysosome relative to the cytosol and activates the enzymes that digest the particles. Which of the following best predicts what will happen to the lysosomal enzymes if the proteins that transport H+ ions from the cytosol into the lysosome are damaged?

The lysosomal enzymes will not become active, since there will be no active transport of H+H+ ions.

Describe the fluid mosaic model. What's "fluid"? What's "mosaic"?

The membrane is a fluid structure with a "mosaic" of various proteins embedded in or attached to a double layer (bilayer) of phospholipids. A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer, hence the "mosaic". The membrane is fluid, hence the "fluid".

How does the presence of saturated versus unsaturated lipids affect membrane fluidity?

The membrane remains fluid to a lower temperature if it has a lot of phospholipids with unsaturated hydrocarbon tails. This is because of the kinks in the tails (where double bonds are located). Unsaturated hydrocarbons can't pack close together as saturated hydrocarbons can, therefore it makes the membrane more fluid.

Hereditary spherocytosis (HS) is a disorder of red blood cells that causes the cells to be smaller and spherical instead of having the usual flattened, biconcave shape. The average diameter of normal red blood cells is 7.2μm, and the average diameter of red blood cells in a person with HS was found to be 6.7μm. The normal red blood cell has an average surface area of 136μm2 and an average volume of 91μm3. Which of the following provides an accurate calculation of the surface area to volume ratio of an HS red blood cell, as well as a prediction of its effect on the efficient transferring of oxygen compared to a normal red blood cell?

The ratio is 0.890.89, and the cells are less efficient at transferring oxygen.

Describe how active transport and gated channels can work together to maintain an electrochemical gradient.

The sodium potassium pump is active transport with gated channels. It pumps out sodium from the cell while pumping potassium into the cell. The plasma membrane helps maintain steep gradients. The concentration of sodium ions inside a resting nerve cell is much lower than outside it. When the cell is stimulated, gated channels that facilitate Na+ diffusion open. Sodium ions then fall down the electrochemical gradient, driven by th4 concentration gradient of Na+and by the attraction of cations to the negative side of the membrane.

Diffusion

The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.

Which of the following transport mechanisms will be affected most directly by a temporary shortage of ATP molecules inside the cell?

The transport of glucose molecules against a concentration gradient

Integral Proteins

Typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane

Certain bacteria can use both ethyl alcohol and acetate as sources of nutrients. In an experiment where both nutrients are available to a bacterial population, the following results were obtained and graphed. What additional procedure would best help determine whether these movements are due to active transport or to passive transport?

Use two additional treatments, one containing only ethyl alcohol and one containing only acetate. Include a substance known to block ATP use by the plasma membrane. Compare the graphs of these two treatments to the original graph.

Turgid

Very firm. a walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.

Beetroot cells contain a family of dark red pigments called betalains. The selectively permeable nature of the beetroot cells keeps the internal environment of the cell separate from the external environment of the cell. Researchers are interested in determining whether the selective permeability of beetroot cells is due to the cell membrane or if it is due to the cell wall. Exposure to cellulase is known to damage the structure of the cell wall. An experiment is set up in which beetroot cells are placed in an aqueous solution with cellulase and in one without cellulase. Which of the following results best refutes the alternative hypothesis that selective permeability is a consequence of the cell wall?

When beetroot cells are placed in a solution with cellulase, the solution remains clear.

Signal transduction

a protein with a binding with a specific shape that fits the shape of a chemical messenger, may cause a conformational change in the protein that relays the message to inside the cell.

Enzymatic activity

an enzyme with its active site exposed to substances in the solution, can carry out sequential steps of a metabolic pathway

transport

either provides a hydrophilic channel across the membrane (selective), or shuttles a substance from one side to the other by changing shape.

Attachment to the cytoskeleton and extracellular matrix (ECM)

elements or microfilaments of the cytoskeleton may be bonded to membrane proteins, helps maintain cell shape and stabilizes the location of certain membrane proteins

Intercellular joining

membrane proteins in other cells may hook together in different types of junctions

Cell-cell recognition

serve as identification tags that are recognized by other cells

Active Transport

the movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins

Facilitated diffusion

the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradient

List 6 roles for membrane proteins

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attatchment to the cytoskeleton and extracellular matrix