Chapter 5 Questions

Phospholipid Structure

1. A phospholipid has a "head" made up of a glycerol molecule attached to a single phosphate group, which is attached to another small molecule. 2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a choline group attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is hydrophilic, which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two fatty acid molecules, which consist of a carboxyl group with a long hydrocarbon chain attached. 5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are hydrophobic, which means they are excluded from water.

Diffusion Two diagrams showing a chamber containing purple and orange balls--one before diffusion and one after diffusion. The chamber is divided into two compartments by a membrane that is permeable to both purple and orange balls. The diagram on the left shows the initial condition, with 9 orange balls on the left side of the membrane and 3 orange balls on the right. There are 2 purple balls on the left and 6 purple balls on the right. The diagram on the right shows the equilibrium state after diffusion has occurred. There are 6 orange balls on the left and 6 orange balls on the right. There are 4 purple balls on the left and 4 purple balls on the right.

1. Orange dye moves independently of purple dye. - always 2. Concentration gradients exist that drive diffusion of both dyes. - only before equilibrium is reached 3. There is no net movement of orange dye from side A to side B. - only before equilibrium is reached 4. Purple due moves only from side B to side A. - never 5. There is no net movement of purple dye. - only at equilibrium

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur. Solution A: 3.21% (m/v) NaCl Solution B: 1.65% (m/v) glucose Solution C: distilled H2O Solution D: 6.97% (m/v) glucose Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl Drag each solution to the appropriate bin.

Crenation: Solution A: 3.21% (m/v) NaCl Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl Solution D: 6.97% (m/v) glucose Hemolysis: Solution B: 1.65% (m/v) glucose Solution C: distilled H2O Neither: none

What concentration of radioactive glucose did the researchers find in the red blood cells of a 15-day-old guinea pig after an incubation time of 30 minutes?

85 mM

Know Hypertonic? Isotonic? Hypotonic?

Hypertonic - shriveled up Isotonic - perfect Hypotonic - bursting

Phospholipid structure:

Nonpolar molecules: hydrophobic, can cross easily and no transport protein required Polar molecules: hydrophilic, have difficulty crossing the hydrophobic part, transport protein required to cross efficiently Ions: hydrophilic, have difficulty crossing the hydrophobic part, transport protein required to cross efficiently

The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive movement of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. Diagram showing facilitated diffusion across the plasma membrane. A channel protein embedded in the membrane allows yellow balls to travel through a channel from the outside of the cell to the inside. A carrier protein embedded in the membrane undergoes a shape change allowing red balls to travel from the outside of the cell to the inside. Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers.

Only channels: ~allow water molecules and small ions to flow quickly across the membrane ~Provide a continuous path across the membrane Only carriers: ~undergo a change in shape to transport solutes across the membrane ~ transport primarily small polar organic molecules Both channels and carriers: ~ are integral membrane proteins ~ transport solutes down a concentration gradient or electrochemical gradient ~ provide a hydrophilic path across the membrane

Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.

Oxygen, water, lipids and carbon dioxide Do NOT: sucrose, ions, proteins

A semipermeable membrane is placed between the following solutions. Which solution will decrease in volume? Solution A: 1.4% (m/v) starch Solution B: 7.62% (m/v) starch

Solution A: 1.4% (m/v) starch

A semipermeable membrane is placed between the following solutions. Which solution will increase in volume? Solution C: 9% (m/v) NaCl Solution D: 12.4% (m/v) NaCl

Solution D: 12.4% (m/v) NaCl

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 Na+ ions into the cell is impeded by the electrical gradient across the plasma membrane. The diffusion of K+ ions out of the cell is impeded by the K+ 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+.

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 hypotheses is a reasonable explanation for the data represented in the graph?

The red blood cells of older guinea pigs have fewer glucose transporter proteins than the red blood cells of younger guinea pigs.

Steps of active transport

Active transport by the sodium-potassium pump follows this cycle. 1. Three Na+ ions from the cytosol bind to the pump. 2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4. 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. 5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.

Identify the trend common to both the 15-day-old and 1-month-old guinea pigs' red blood cells.

Both experienced the most rapid uptake of glucose at the beginning of the experiment.

What is the main difference between the trends for the 15-day-old and 1-month-old guinea pigs' red blood cells?

The younger guinea pig's cells took up more glucose than the older guinea pig's cells at all incubation times.

Which variable is the dependent variable--the variable that depended on the treatment and was measured by the researchers? Is the dependent variable on the x-axis or the y-axis?

concentration of radioactive glucose; on the y-axis

Exocytosis and Endocytosis

exocytosis: ~requires fusion of vesicles with the plasma membrane ~ secretes large molecules out of the cell ~ increses the surface area of the plasma membrane endocytosis: ~ forms vesicles from inward folding of the plasma membrane ~ decreases the surface area of the plasma membrane both: ~ transported substances never physically cross the plasma membrane ~ requires cellular energy

The plasma membrane

extracellular fluid: hydrophobic cytoplasm: hydrophilic plasma membrane:phospholipids top of membrane protein: hydrophilic middle of membrane protein: hydrophobic bottom of membrane protein: hydrophilic

A graph showing glucose uptake in guinea pig red blood cells of different ages. s glucose uptake into cells affected by age? Glucose, an important energy source for animals, is transported into cells by facilitated diffusion using protein carriers. In this exercise, you will interpret a graph from an experiment in which researchers incubated guinea pig red blood cells in a 300 mM (millimolar) radioactive glucose solution at pH 7.4 at 25°C. Every 10 or 15 minutes, they removed a sample of cells from the solution and measured the concentration of radioactive glucose inside those cells. Cells came from either a 15-day-old guinea pig or a 1-month-old guinea pig. The graph at left shows the data from the experiment. Which variable is the independent variable--the variable that was controlled by the researchers? Is the independent variable on the x-axis or the y-axis?

incubation time; on the x-axis

Active transport by sodium-potassium pump

outside cell: [Na+] high, [K+] low excess (+) charge pump: 3 Na out, 2 K in inside the cell: [Na+] low [K+] high excess (-) charge

The glucose-sodium cotransporter In many animal cells, the uptake of glucose into the cell occurs by a cotransport mechanism, in which glucose is cotransported with Na+ ions.

outside cell: [Na+] high [glucose] low transporter: glucose and Na+ go down inside cell: [Na+] low [glucose] high 1. Na+ moves down its electrochemical gradient. 2. Glucose moves against its concentration gradient.

What do the blue dots represent?

the concentration of radioactive glucose found in a 1-month-old guinea pig's red blood cells after different incubation times

What do the red dots represent?

the concentration of radioactive glucose found in a 15-day-old guinea pig's red blood cells after different incubation times