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14-15, 20
9-10, 21

Cell Membrane Dynamics!

1. What does selective permeability mean and why is that important to cells?
Why important to all life?

external image support.gif This dotted line represents a selectively permeable membrane because only the water molecules can fit through the spaces while the molecules of the other substance are too large to fit through. Kim K. Red Team

2. What is an amphipathic molecule?

An amphipathic molecule, is a molecule that has both a hydrophilic or polar end and a hydrophobic or non polar end. These molecules are also an important part of the human body, because they act like a transporter for hydrophobic material throughout the hydrophilic environment in the body, to give you an idea an example of this is that lipids can not move in the body with the blood unless it is bonded to the amphipathic molecules, if this does not happen the lipids will make obstructions in the vessels.
-Brett S.
picture of amphipathic molecule

Not a great video but, closest I could find for the idea.

3. What were the ideas concerning the plasma membrane models below:
a. Gorter and Grendel - reasoned that cell membranes must actually be phospholipid bilayers. With the conclusion that a phospholipid bilayer was the main fabric of a membrane, the next question was where to place the proteins.

b. Davson and Danielli - proposed a sandwich model: a phospholipid bilayer between two layers of proteins.

c. Singer and Nicolson - proposed that membrane proteins are dispersed and individually inserted into the phospholipid bilayer, with only their hydrophilic regions producing far enough from the bilayer to be exposed to water.

This is a very short video, but does a great job explaining the Cellular Membrane.

- Alina Dyak

4. Describe the freeze fracture technique and why is it useful in cell biology.
In the process of freeze fracturing a cell is not only getting ready for electron microscopy, but the cell membrane is getting split into its two layers which helps to show the fine structures (ex; tissues) of the membrane's interior with protein particles spread through out in the smooth matrix. This technique is also able to show that proteins are embedded in the phospholipid bilayer of the membrane and it supports the fluid mosaic model. This is useful in cell biology because it is able to help with future research, support current ideas and even completely dismiss other models, eventually moving us forward in the world of science.

external image ech3-16.jpg
-Dahlia M.

5. How is the fluidity of cell membrane’s maintained?
The phosphopids constantly switch places laterally and sometimes vertically. The temperature must be warm enough to prevent the membrane from freezing (mostly for saturated fats, since unsaturated fats are spaced apart due to double bonds). The addition of cholesterol molecules between the lipids makes them less flexible but keeps them apart, making it harder for them to freeze.
external image fluid_%20mosaic_model.jpg
-Sam V

6. For each structure in the diagram below briefly list it’s function:

1. extracellular matrix is part of the cells growth rate along with providing support for the cell

2. Glycoprotein is created in the cell when a carbohydrate covalently binds to a protein as a part of cell recognition

3. Carbohydrate- in the membrane they contribute to cell recognition, they differ from cell to cell making it easier for cells to recognize similar cells with matching carbs.

4. Glycolipid is created when a carbohydrate covalently bonds to a lipid in the cell, part of cell recognition

5. Extracellular side of membrane is the side that is the most superficial part of the cell, top layer of the phospholipid bilayer making up the membrane.


6. Microfilaments of C

ytoskeleton- bind to membrane proteins in order to maintain the cell shape along with stabilizing certain proteins in the membrane.

7. Cholesterol- in the membrane it helps to keep the fluidity of the membrane by breaking up the phospholipids here and there, hindering solidification.

8. Peripheral proteins are proteins that are on the surface of the membrane but not tightly connected to it. They help to strengthen the cells frame work.

9. Integral proteins are embedded into the lipid bilayer throughout the membrane also strengthening the framework of the cell.

10.Cytoplasmic side of membrane is the one layer of phospholipids where the proteins are embedded into

(long and boring, but if you move it around it gives extra information on the parts of the cell and their functions)

Taihlor C

7. List the six broad functions of membrane proteins.

Transport- Channel through membrane
Enzymatic Activity- Break up and build up substrates
Signal Transduction- Chemical Messenger
Cell-cell Recognition- I.D. tags
Intercellular Joining- Hooking cells together
Attachment to the Cytoskeleton and ECM- Helps maintain cell’s shape and size

external image images?q=tbn:ANd9GcTRnTbhirdnUlS7vD6j7BGRJCsMIiIE7w2anE1EFIt-n96gC2M&t=1&usg=__peZOLinIdGf2s17Ac0mk0IP6jW8=

This picture shows integral proteins, peripheral proteins, and glycoproteins. Glycoproteins have the function of cell-cell recognition. The other proteins are for Transport and the other functions.

-Mike G

8. How do glycolipids and glycoproteins help in cell to cell recognition?

Glycolipids are lipids that are covalently attached to a carbohydrate. Glycoproteins are proteins that are covalently attached to a carbohydrate.
The carbohydrates on the external side of the plasma membrane vary from species to species, among individuals of the same species, and even from one cell type to another in a single individual. The diversity of the molecules and their location on the cell’s surface enable membrane carbohydrates to function as markers that distinguish one cell from another. For example, the four human blood types designated A, B, AB, and O reflects variation in the carbohydrate on the surface of red blood cells.


external image f21-7a_abo_blood_types_c.jpg

In this picture it shows how each blood type contains different receptors (antigen) on its plasma membrane.

-Mike G

9. Why is membrane sidedness an important concept in cell biology?
REvise in plain speak please!

Molecules that start on the inside of the ER finish on the outside of the Plasma membrane. Every protein in the membrane has directional orientation. The asymmetrical distribution of proteins, lipids, and their associated carbohydrates in the plasma membrane are done when the membrane is being constructed by the ER and Golgi apparatus.

external image membrane.jpgexternal image bj3690199f01.jpg

10. How has our understanding of membrane permeability changed since the discovery of aquaporins?
external image ERTkE91ICB8?h=350&w=425

They are proteins inside a the cell membrane and they regulate water flow. An aquaporin is like the pipes of a house. They have been in-connection with human genetic diseases too. They show that water is transported through the membranes.

11. What is diffusion and how does a concentration gradient relate to passive transport?

Diffusion- The tendency for molecules of any substance to spread out evenly into the available space. Concentration gradient relates to passive transport because when a substance is seperated by a membrane it moves from high concentration to low concentration, just as any other substance. When it is seperated by a semipermeable membrane is uses no energy going from high concentration to low concentration.Concentration gradient is needed for passive transport.
external image passive_transport2.gif

13. Why is free water concentration the “driving” force in osmosis
Because the concentration of free water in the different spaces creates a concentration gradient and drives the H2O to travel down its gradient, just like molecules during diffusion.
osmosis.jpgH2O traveling down its concentration gradient
-Josh S.

14. Why is water balance different for cells that have walls as compared to cells without walls?
Cells without walls are best in isotonic solutions, which has no net movements of water across the plasma membrane.
In a hypertonic environment cells water will leave the cell and it will shrivel and die.
In a hypotonic environment the cell will absorb water and swell and lyse (burst).
Cells with walls are best in hypotonic solution because the water will expand the elastic wall and make it turgid (firm), which is a healthy state for cells with walls.

This video shows red blood cells in isotonic, hypertonic and hypotonic solutions. The video doesn't have sound. =(
-Fernanda R.

15. Label the diagram below:


A) Animal Cell: An animal cell fares best in an isotonic environment unless it has special adaptations to offset the osmotic uptake and loss of water.
B) Plant Cell: Plant cells are turgid (firm) and generally healthiest in a hypotonic environment, where the uptake of water is eventually balanced by the elastic wall pushing back on the cell.

Open doc above pic to see rest of labels

Ryan H

16. What is the relationship between ion channels, gated channels and facilitated diffusion – write 1 -2 sentences using those terms correctly.

Many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane, which is called facilitated diffusion. the way that things pass through the membrane are ion channels which are sometimes gated channels. A stimulus, either a electric shock or chemical signal, causes them to open or close.

Alecia Seliga

17. How is ATP specifically used in active transport?

ATP gives the system energy, allowing it to change shape of certain channels allowing a molecule to move across a membrane against its gradient, pushing to the outside of a cell. ATP is constantly used, because the molecules are moving against their concentration gradient.
-Sam B.

-Sam B.
really boring, but helpful to understand the process

18. Define and contrast the following terms: membrane potential, electrochemical gradient, electrogenic pump and proton pump.
Hey! Fix me!

Membrane Potential: The voltage across a membrane, affects the traffic of charged substances across the membrane
Electrochemical gradient:the combination of the concentration gradient adn an electric forceelectrochemical-gradient.jpg
electrogenic pump: a transport protein that generates voltage through the membrane
proton pump:transports hydrogen ions out of the cell
proton_pump.jpg Sam B.

19. What is cotransport and why is an advantage in living systems?
Cotransport is an ATP powered pump that transports a specific solute to different areas of the body. This indirectly drives the active transport of several other solutes. This process allows us to identify parasites withing the body quickly and effectively and hopefully exterminate them totally from living organisms.
-Sam B.

20. What is a ligand?
Ligands is a general term for any molecule that binds to a specific receptor site of another molecule. An example would be Low density lipoproteins by binding to LDL receptors on membranes and then entering through endocytosis.

external image lock_key.gif
This picture shows different ligands,

21. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated endocytosis.

Phagocytosis- a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole.

Pinocytosis- the cell gulps droplets of extracellular fluid into tiny vesicles.
Receptor-mediated endocytosis- enables the cell to acquire bulk quantities of specific substances.

-Kelly Sinclair