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BIO Chapter 4

Page history last edited by Shelly Turner 11 years, 4 months ago

Chapter 4:  Cells and Their Environment

 

 

 

I.       Passive Transport

A.  Movement of substances across the cell membrane that does not require energy (moving WITH the gradient)

B.  Concentration gradient - difference in concentration of a substance across space

C.  Equilibrium - occurs when the concentration of a substance is equal across space

D.  Types of Passive Transport

1.    Diffusion - movement of a substance from an area of higher concentration to an area of lower concentration that is caused by the random movement of the particles of that substance

 

 

Diffusion is…

 

Why we can smell things

Why the whole spoon gets hot when it's only half in the tea

Why smoke spreads to fill a whole room

     

 

 

2.    Osmosis - diffusion of water, can occur in three patterns of movement 

a)    Water moves OUT of the cell - occurs when the cell is in a hypertonic environment - the environment contains a higher level of dissolved substances (and therefore a lower concentration of water) than the cytoplasm of the cell therefore water moves out of the cell to achieve a balance

b)    Water moves IN to the cell - occurs when the cell is on a hypotonic environment - the environment contains a lower level of dissolved substances (and therefore a higher concentration of water)  than the cytoplasm of the cell therefore water moves into the cell to achieve a balance

c)     No NET movement of water - occurs when the cell is in a isotonic environment - the environment contains an equal level of dissolved substances (and therefore an equal concentration of water) than the cytoplasm of the cell therefore water molecules  move equally into and out of the cell to maintain a balance            

 

           

3.    Facilitated Diffusion - transportation of substances across a cell membrane with the help of carrier proteins; only works when moving down a concentration gradient 

a)     Carrier proteins bind a specific type of and carry the solute to the other side of the membrane. The carrier then discharges the solute and reorients in the membrane to its original state. Typically, a given carrier will transport only a small group of related molecules

b)    Ion Channels do not bind the solute, but are like hydrophilic pores through the membrane that open and allow certain types of solutes, usually inorganic ions, to pass through. In general, channels are quite and are quite a bit faster than carrier proteins. Additionally, many channels contain a "gate" which is functions to control the channel's permeability. When the gate is open, the channel transports, and when the gate is closed, the channel is closed. 

 

II.     Active Transport

A.  Movement of substances across the cell membrane that does require energy (moving AGAINST the gradient, aka up the concentration gradient)

B.  Types of Active Transport

1.    Endocytosis - movement of substances into the cell by engulfing it in a vesicle (pouch) 

 

a)     Phagocytosis - the cell membrane folds around the molecule or substance, isolating it for later use in a vacuole called a phagosome. (Phagocytosis is literally translated as "cell eating.")

b)    Pinocytosis – the cell membrane folds around the molecule or substance, and it is dissolved into the interior of the cell. Molecules such as proteins and other water-soluble substances are ingested this way. (Pinocytosis is literally translated as "cell drinking.") 

2.    Exocytosis - movement of substances out of the cell by expelling it from a vesicle (pouch) 

3.    Sodium – Potassium Pump  - Transport of 3 sodium (Na+) ions out of the cell and 2 potassium (K+)  ions into the cell.  Sodium ions are usually more concentrated outside of the cell and potassium is usually more concentrated inside the cell; therefore the movement is against the gradient.  Energy for this is supplied by ATP, often this pump uses much of the energy produced by the cell. 

a)    Steps in the Sodium-Potassium Pump:

(1)  Three sodium ions inside the cell bind to the pump.  Because energy is needed a phosphate group from ATP also binds to the pump.

(2)  The pump changes shape, enclosing the Na+

(3)  The pump changes again to release the Na+ on the outside of the cell

(4)  The open pump binds to 2 K+

(5)  The phosphate group is released allowing the pump to close

(6)  The pump changes and two K+ are released inside the cell  

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