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Cell Membrane |
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Cell Membrane |
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How does the Cell Membrane do its job?
A. Functions of the Cell Membrane:
1. Cell to cell communication
2. Selective Permeability (Selectively/Semi Permeable)
3. Boundary
B. Structure of the Cell Membrane:
1. Lipid Bilayers (2 layers of fats and oils)
2. Protein Intersperses (Food spread out)
� Inside and outside of the cell-H2O
� Proteins and Channel (tunnel) inside of cell
� Hydrophobic-afraid of water
� Hydrophilic-loves water
C. Relation of Structure and Function
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STRUCTURE |
FUNCTION |
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Outside layer of cell: Cell Membrane
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Boundary |
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Channel-entering or leaving by size |
Selectively Permeable |
BACKGROUND
Example: Salt Water Solution
Solution: A homogeneous (uniform) mixture that can be physically separated (heating the water so it will evaporate and we will be left with only salt.)
Solvent: The material (substance) that the solute is dissolved in (Water)
Solute: The material being dissolved (Salt)
**Water is the universal solvent**
D. Transport (absorb and circulate):
1. Passive Transport-no energy required
a. Diffusion-material moved from an area of high concentration to an area of low concentration
i. Osmosis- diffusion of water across a semi-permeable membrane from a more to less area of water
� Tonicity-refers to the particles in the H2O
� Isotonic-If a salt concentration (solution) inside and outside of a red blood cell (RBC) is .9% salt, the cell won�t change. The solution outside of the cell is isotonic to the solution inside of the cell.
� Hypertonic-If the salt solution inside of the cell is .9% salt (99.9 % water) and the solution outside of the cell is 10% salt (90 % water), the water inside of the cell will leave causing the RBC to shrink. The salt solution is hypertonic to the cell and so H2O leaves the cell.
� Hypotonic- If the salt solution inside of the cell is .9% salt (99.9 % water) and the outside of the cell is pure water (no particles), the outside water will enter the cell, causing the RBC to burst (hemolysis). The pure H2O is hypotonic relative to the cell.
� Example: Egg experiment: The egg was first placed in vinegar. A chemical reaction (bubbling) was caused and the outer membrane deteriorated. Then it was placed in Karo Syrup, which is a sugar solution. When taken out of the sugar solution we were able to observe the egg. It was lighter, softer (mushy), and brown because the water in the egg left. The sugar solution is hypertonic to the cell/egg and so H2O leaves the cell. The next step was placing the egg in pure water. The water outside entered the egg which made the cell even bigger (eventually causing it to explode.) The pure H2O is hypotonic relative to the egg.
b. Facilitated Diffusion- membrane molecules help move molecules from high to low concentration.
2. Active Transport-requires energy
� It is the movement of materials from an area of low concentration to an area of high concentration with the expenditure of energy. (Ex: water-fresh water organism)
� Membrane proteins do the job (Pumps)
� Endocytosis-cells take in large molecules
� Exocytosis-cells let out large molecules
E. Cell to Cell Communication:
1. Receptors (proteins)-recognize chemical symbols
a. Chemical message
b. Receptors recognize message by the shape of the molecule acting as a message. The message must �fit� the receptor.
c. To block the message from getting through-the receptor may be blocked. This is accomplished by attaching another molecule (�blocker�) which prevents the message from attaching itself to the receptor.
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