Membrane Structure And Function Flashcards
Label the components in this diagram of the fluid mosaic model of membrane structure. Indicate the regions that are hydrophobic and those that are hydrophilic.
a. phosphate head - hydrophilic
b. phospholipid bilayer
c. hydrocarbon tail - hydrophobic
d. hydrophobic region of protein
e. hydrophilic region of protein
Cite some experimental evidence that shows that membrane proteins drift.
In hybrid human/mouse cells, membrane proteins rapidly intermingle (Frye and Edidin experiment).
List the six major kinds of functions that membrane proteins may form
- Transport
- Enzymatic activity
- Signal transduction
- Intercellular joining
- Cell-cell recognition
- Attachment to cytoskeleton and ECM
What types of molecules have difficulty crossing the plasma membrane? Why?
Ions and larger polar molecules, such as glucose. They are impeded by the hydrophobic center of the plasma membrane’s lipid bilayer. Passage through the center of a lipid bilayer is not fast even for small, polar water molecules.
A solution of 1 M glucose (side A) is separated by a selectively permeable membrane from a solution of 0.2 M fructose and 0.7 M sucrose (side B). The membrane is not permeable to the sugar molecules. Indicate which side initially has more free water molecules and which has fewer. Show the direction of osmosis
Side A initially has fewer free water molecules. More water molecules are clustered around the glucose in the 1 M solution than around the .9 M combined concentration of the fructose and sucrose. Water will move by osmosis from side B to A.
A) What osmotic problems do freshwater protists face?
B) What adaptations may help them osmoregulate?
A) The protists will gain water from their hypotonic environment.
B) They may have membranes that are less permeable to water and contractile vacuoles that expel excess water.
A) The ideal osmotic environment for animal cells is ______.
B) The ideal osmotic environment for plant cells is ______.
A) isotonic
B) hypotonic
Why is facilitated diffusion considered passive transport?
Although it may speed diffusion, facilitated diffusion is a till passive transport because the solute is moving down its concentration gradient; the process is driven by the concentration gradient and not the energy expended by the cell.
The sodium-potassium pump, the major electrogenic pump in animal cells, exchanges sodium ions for potassium ions, both of which are cations. How does this exchange generate a membrane potential?
Three sodium ions are pumped out of the cell for every two potassium ions pumped in, resulting in a net movement of positive charge from the cytoplasm to the extracellular fluid.
A) How is cholesterol, which is used for the synthesis of other steroids and membranes, transported into human cells?
B) Explain why cholesterol accumulates in the blood of individuals with the disease familial hypercholesteremia.
A) Human cells use receptor-mediated endocytosis.
B) LDL receptor proteins in the plasma membrane are defective, and low-density lipoproteins cannot bind and and be transported from the blood into the cell.
Create a concept map to illustrate your understanding of osmosis.
The diagram illustrates passive and active transport across a plasma membrane.
a) Which section represents facilitated diffusion? How can you tell? Does the cell expend energy in this transport? Why or why not? What types of solute molecules may be moved by this type of transport?
b) Which section shows active transport? List two ways you can tell.
c) Which section shows diffusion? What types of solute molecules may be moved by this type of transport?
d) Which of these sections are considered passive transport?
a) II represents facilitated diffusion. The solute is moving through a transport protein and down its concentration gradient. The cell does not expend energy in this transport. Polar molecules and ions may move by facilitated diffusion.
b) III represents active transport because the solute is clearly moving against its concentration gradient and the cell is expending ATP to drive this transport against the gradient.
c) I illustrates diffusion through the lipid bilayer. The solute molecules must be nonpolar or very small polar molecules.
d) I and II. Both diffusion and facilitated diffusio are considered passive transport because the solute moves down its concentration gradient and the cell does not expend energy in the transport.
Glycoproteins and glycolipids are important for
a) facilitated diffusion.
b) active transport.
c) cell-cell recognition.
d) cotransport.
e) signal-transduction pathways.
c) cell-cell recognition
A single layer of phospholipid molecules coats the water in a beaker. Which part of the molecules will face the air?
a) the phosphate groups
b) the hydrocarbon tails
c) both head and tail because the molecules are amphipathic and will lie sideways
d) the glycolipid regions
e) the phospholipids would dissolve in the water and not form a membrane coat
b) the hydrocarbon tails
Which of the following is not true about osmosis?
a) it is a passive process in cells without walls, but an active one in cells with walls.
b) water moves from a hypotonic to a hypertonic solution.
c) solute molecules bind to water and decrease the water available to move.
d) it can occur more rapidly through channel proteins known as aquaporins.
e) there is no set osmosis between isotonic solutions
a) it is a passive process in cells without walls, but an active one in cells with walls
Support for the fluid mosaic model of membrane structure comes from
a) the freeze-fracture technique of electron microscopy.
b) the movement of the proteins in hybrid cells.
c) the amphipathic nature of many membrane proteins.
d) both a and c.
e) all of the above.
e) all of the above
Facilitated diffusion of ions across a cellular membrane requires _____ and the ions move _____.
a) energy and transport proteins…against their electrochemical gradient
b) energy and transport proteins…against their concentration gradient
c) cotransport proteins…against their electrochemical gradient
d) transport proteins…down their electrochemical gradient
e) transport proteins…down their concentration gradient
d) transport proteins…down their electrochemical gradient
Which of the following is the most probable description of an integral, transmembrane protein?
a) amphipathic with a hydrophiic head and a hydrophobic tail region
b) a globular protein with hydrophobic amino acids in the interior and hydrophilic amino acids arranged around the outside
c) a fibrous protein coated with hydrophobic fatty acids
d) a glycolipid attached to the portion of the protein facing the exterior of the cell and cytoskeletal elements attached to the portion facing inside the cell
e) a middle region composed of (symbol) helical stretches of hydrophobic amino acids, with hydrophilic regions at both ends of the protein
e) a middle region composed of (symbol) helical stretches of hydrophobic amino acids, with hydrophilic regions at both ends of the protein
The fluidity of membranes in a plant in cold weather may be maintained by increasing the
a) number of phospholipids with saturated hydrocarbon tails.
b) action of an H+ pump.
c) concentration of cholesterol in the membrane.
d) proportion of peripheral proteins.
e) number of phospholipids with unsaturated hydrocarbon tails.
e) number of phospholipids with unsaturated hydrocarbon tails.
An animal cell placed in a hypotonic environment will
a) plasmolyze.
b) shrivel.
c) become turgid.
d) become flaccid.
e) burst (lyse).
e) burst (lyse).
Which of the following is not true of carrier molecules involved in facilitated diffusion?
a) They increase the speed of transport across a membrane.
b) They can concentrate solute molecules on one side of the membrane.
c) They may have specific binding sites for the molecules they transport.
d) They may undergo a change in shape upon binding of solute.
e) They do not require an energy investment from the cell to operate.
b) They can concentrate solute molecules on one side of the membrane.
The membrane potential of a cell favors
a) the movement of cations into the cell.
b) the movement of anions into the cell.
c) the action of an electrogenic pump.
d) the movement of sodium out of the cell.
e) both b and d.
a) the movement of cations into the cell.
Cotransport may involve
a) active transport of two solutes through a transport protein.
b) passive transport of two solutes through a transport protein.
c) ion diffusion against the electrochemical gradient created by an electrogenic pump.
d) a pump such as the sodium-potassium pump that moves ions in two different directions.
e) transport of one solute against its concentration gradient in tandem with another that is diffusing down its concentration gradient.
e) transport of one solute against its concentration gradient in tandem with another that is diffusing down its concentration gradient.
Exocytosis may involve all of the following except
a) ligands and coated pits.
b) the fusion of a vesicle with the plasma membrane.
c) a mechanism to export some carbohydrates during the formation of plant cell walls.
d) a mechanism to rejuvenate the plasma membrane.
e) a means of exporting large molecules.
a) ligands and coated pits.
