Period 7th10/13 /2013

RAVEN CHAPTER 5 GUIDED NOTES: MEMBRANES

1. Describe the structure of a phospholipid molecule. Be sure to describe their behavior in

relationship to water. Phospholipids have large polar heads and non-polar tails (due to

hydrocarbons). Water molecules are attracted to the polar heads (because water has polar bonds

where Oxygen is more negative and H are more positive). The non-polar tails do not like to be in

water because of water's polarity. So when phospholipids are dumped into water, they will

spontaneously arrange themselves so that the polar heads are in water, but the non-polar tails are

not. This can take form as a bilayer

2. What happens when a collection of phospholipids molecules are placed in water? They would

arrange themselves into two layers. The hydrophilic heads would face the water [or whatever the

liquid may be] while the hydrophobic tails would hide inside the layers. Since the phospholipid

molecules aren't bonded to one another, the layer would be fluid and individual molecules would

easily move around.

3. Explain the significance of this behavior in relationship to the evolution of life. The fact that it

will spontaneously arrange itself into a bilayer. Heads in toward each other, tails facing out. It

becomes a semi-permeable membrane.Not only to they form a bilayer but in smaller amounts

they will form a micelle. A micelle allows entrapment of other molecules inside it and forces

these other molecules to interact together.

4. What is meant by the phrase “the plasma membrane is fluid”? The plasma membrane is "fluid"

because of movement of substances across the membrane. c. The bilayer permits diffusion of

certain lipid-soluble substances.

5. Explain the fluid mosaic model. The fluid mosaic model explains how proteins and other

components of the cell membrane diffuse.

6. How is the fluidity of the cell membrane altered? It can be altered depending on the type of

hydrophobic molecules that make up the membrane!The fluidity of the membrane can then affect

the proteins that are found embedded in it.. it can change their activity and kinetics (how they

work)The fluidity of the membrane can also be altered by some hormones found in circulation

7. Describe the components of the cell membrane. Explain the function of each and give an

example

a. The most fundamental "backbone" if you will is the phospholipid. They have two fatty acid

nonpolar tails (hydrophobic = avoid water) and polar heads (hydrophilic - water loving). They

form a bilayer with the tails facing the middle and the heads facing the outside (since outside

cytosol is water).

b. Integral Proteins - transverse the membrane and serve many functions such as transporting

things across

c. Cholesterol - tons of these molecules in the membrane help maintain the fluidity

d. Glycocalyx - oligosaccharide (carb / sugar) molecule that are often attached to either the

phospholipid or various proteins. They are involved in cell - cell recognition.

8. List and briefly describe the different classes of membrane proteins and the roles they play.

1. They serve as channels across the lipid bilayer.

2. They serve as carrier molecules which transfer substances across the membrane.

3. They serve as docking-marker acceptors that bind lock and key fashion with the docking

markers of secretory vesicles.

4. They serve as membrane bound enzymes that control specific chemical reactions at either the

inner or outer cell surface.

5. They serve as receptors that recognize and bind with specific molecules in the cell's

environment.

6. They serve as cell adhesion molecules.

7. They are important is the cell's ability to recognize "self" as in cells of the same type.

9. Describe how the structure of membrane proteins allows some proteins to be permanently

anchored within the cell membrane as a transmembrane protein whereas other proteins can move

freely about the surface of the membrane. Membrane-bound proteins have short hydrophobic

stretches (usually helices) that allow the membrane to be stably anchored in the membrane. This

does not preclude these proteins from moving laterally across the membrane surface. Some

membrane proteins might be anchored to cytoplasmic structures that restrict this lateral

movement. Such lateral movement is important in membrane-protein functions, which often

require cross-linking for activation.

10. The cell membrane is selectively permeable. Explain what that means. Which molecules

easily cross the membrane? How are molecules transported that do not easily cross the

membrane? Selective permeability means that the cell membrane has some control over what can

cross it, so that only certain molecules either enter or leave the cell. Molecules can cross the

plasma membrane in three main ways.Molecules that are not polar or ion molecules. That is

because they won't be stopped by the hydrophobic tails and they will have the acknowledgement

to pass through the cell membrane thanks to little resistance. The large, hydrophilic molecules

are the molecules that have difficulty passing through the membrane. The transport proteins have

a hydrophilic channel which is used as a tunnel to allow the molecule to pass through by

avoiding the lipid bilayer.

11. Define the following

a. Diffusion - the process of passively(without loss of energy) movement of any substance from

higher concentration to the lower concentration

b. Facilitated Diffusion - a type of passive transport that allows substances to cross membranes

with the assistance of special transport proteins.

c. Osmosis - the process that causes a liquid (especially water) to pass through the wall of a

living cell

d. Hypotonic - has a low osmotic concentration pressure.

e. Hypertonic- has a high osmotic concentration pressure.

f. Isotonic- Having the same concentration of solutes as the blood: an isotonic saline solution.

12. What is happening in the diagram below? The diagram looks like it is going through the

process of osmosis which is from hypotonic to hypertonic low to high concentration.

13. Explain how facilitated diffusion works and give an example. Facilitated diffusion is the

spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological

membrane down their concentration gradient.Glucose, sodium ions and chloride ions are just a

few examples of molecules and ions that must efficiently get across the plasma membrane but to

which the lipid bilayer of the membrane is virtually impermeable. Their transport must therefore

be "facilitated" by proteins that span the membrane and provide an alternative route or bypass.

14. What is the function of aquaporins? Why are they necessary? Aquaporins are protein

molecules embedded in the phospholipid bilayer of some cells.They transport water across the

cell membrane. is necessary to keep cells hydrated during periods of drought .

15. What do animal & plant cells do when placed in solutions that are:

a. Hypotonic -when a animal cell is placed in a hypotonic solution (a solution containing less

solute particles than inside cell e.g water) molecules move from a high water potential to a low

one because diffusion. net movement is into the cell. because of this the cell swells and

eventually burst. this is osmotic shock. plant cell have a cell wall so in a hypotonic solution the

cell swells but doesn't not burst because of the strong structure of the cellulose cell wall.the cell

becomes turgid.

b. Hypertonic- in a hypertonic solution the net movement is out of the cell. the cell shrinks this is

called crenation.- Animal Cell in a hypertonic solution the net movement is out of the cell

because of the high solute conc outside the cell. the cell membrane begins to pull away from the

cell wall. the cell is plasmolysed. when fully plasmolysed it is irreversible. - Plant cell

c. Isotonic -isotonic solution is when the cell content has the same solute potential as the solution

the cell is in. therefore no net movement of molecules.

16. How does the Paramecium maintain osmoregulation? A Paramecium has a plasma

membrane that is much less permeable to water than other membranes of most cells. it uses

contractile vacuoles to pump out excess water that enters because it is in a hypotonic

solution(fresh water).

17. What is the difference between exocytosis and endocytosis? Endocytosis takes material into

the cell by infolding of the cell membrane. Exocytosis releases large amounts of material.

18. Distinguish between pinocytosis and phagocytosis. Phagocytosis means to engulf a solid

objects and pinocytosis means to engulf a liquid object but both forms of endocytosis.

19. Describe an example of receptor-mediated endocytosis. Receptor-mediated endocytosis

(RME) is a process by which cells internalize molecules (endocytosis) by the inward budding of

plasma membrane vesicles containing proteins with receptor sites specific to the molecules being

internalized. One example of receptor-mediated endocytosis important in human physiology is

the main mechanism by which cholesterol is taken up by cells, in particular, liver cells.

20. How do active and passive transport differ? Active transport uses energy and passive

transport doesn't.Active transport requires the cell to use its own energy,while passive transport

doesn't.Active transport is the flow of substances from a lower concentration to a higher

concentration gradient which uses energy in the form of ATP whereas Passive Transport in

contrast, is the flow of substances from higher concentration to a lower concentration gradient

without using energy and it continues until an equilibrium is reached.

21. The sodium-potassium pump uses to pump out of the cell and into the cell.

22. Define coupled transport and give an example. uses ATP-ase and that it pumps three sodium

ions out of the cell for every two potassium ions pumped in.

23. Define countertransport and give an example. it's also called second type active transport,

that can move a substance along its electrochemical gradient, while an other substance is carried

in the opposing direction of its electrochemical gradient. It is Antiport only if one of the

substances are getting out, and the other, getting in.