Post on 12-Nov-2014
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1. Structure of Plasma membrane
* Two-layered structure:
lipid bilayer
*Made of lipid molecules
with protein molecules in
the lipid layer.
**PROTEINS aid in the movement of materials through the membrane
hydrophobictails
hydrophilicheads
hydrophilicheads
extracellular fluid(watery environment)
cytoplasm(watery environment)
phospholipid
bilayer
tails(hydrophobic)
head(hydrophilic)
Polar Head
Non-Polar Tails
* Bilayer can be considered a liquidliquid
FLUID MOSAIC MODEL: plasma membrane : made up of molecules that are free to flow among one another.
Kinds and arrangements of proteins + lipids vary from one membrane to another and give each type of membrane specific permeability properties.
Proteins
Membrane movement animation
Polar heads love water & dissolve.
Non-polar tails hide from water.
Carbohydrate cell markers
Fluid Mosaic Model of the cell
membrane
Outside of cell
Inside of cell (cytoplasm)
Lipid Bilayer
Proteins
Transport Protein Phospholipids
Carbohydratechains
Structure of the Cell Membrane
Go to Section:
Animations of membrane
structure
1. Maintaining a BALANCE in a CELL
Cells Maintain HOMEOSTASIS : internal balance
Selective permeability : allows
some materials to pass through
membrane while rejecting others.
Diffusion
Movement of molecules high concentration to lower concentration
Example: skunk, perfume, night after a dinner at Taco Bell!
1 A drop of dye is placed in water.
2 Dye molecules diffuse into the water; water molecules diffuse into the dye.
drop of dye
pure water
3 Both dye molecules and water molecules are evenly dispersed.
Diffusion animation
Osmosis
The diffusion of Water from areas of high concentration to areas of low concentration
Animation: How Osmosis Works
Transport across membranes
Passive transport of water by Osmosis• a. Isotonic
• b. Hypertonic
• c. Hypotonic
Solution concentration of water (solvent) outside of the cell is the same as concentration inside the cell (Animal cell normal / plant flaccid)
Isotonic Solution:
Hypotonic Solution: concentration of water (solvent)
outside the cell is higher than concentration inside the cell. Water rushes into the cell!
Turgor pressure: Pressure that builds in a plant cell as a result of osmosis. Makes a plant cell firm. (Turgid) Plant cells are healthiest in a hypotonic environment.
Lysed: pressure builds in animal cell (burst)
Hypertonic Solution: concentration of water (solvent) outside cell is lower than concentration inside the cell.
Water rushes out of the cell!
Plasmolysis: loss of water from within a plant cell, causing cytoplasm to shrink, pulling inner plasma membrane away from cell wall. (wilting of plants)
Crenation: (crenates: shrinks) animal cell loses water and it shrinks (collapses)
What type of solution are these cells in?
A CB
Hypertonic Isotonic Hypotonic
(a) isotonic solution (b) hypertonic solution (c) hypotonic solution
10 micrometers
equal movement of waterinto and out of cells
net water movement out of cells
net water movement into cells
Passive transport : movement of substances across plasma membranes without additional energy
Facilitated diffusion: diffusion of materials across a plasma membrane by transport (channel) proteins.
5. PASSIVE TRANSPORT: No energy required for this to happen
Active Transport : gradient from low to high. Energy is required.
Proteins throughout the membrane are “carriers” used for this purpose.
6. ACTIVE TRANSPORT: Requires energy in the form of ATP
Na+ ions: moved out of cell K+ ions: moved by the
same carrier into the cell
(This process is important in nerve and muscle function.)
Sodium-potassium pump Na out K in ACTIVE TRANSPORT = ATP
7. TRANSPORT of 7. TRANSPORT of LARGELARGE PARTICLESPARTICLES
Endocytosis (Endo = In): cell surrounds and takes in material from environment. Material does not pass through the membrane; instead, it is engulfed and closed by a portion of
membrane and cytoplasm. Pinocytosis: water
Phagocytosis: food/ minerals/ large particles
Exocytosis (Exo = Out): transport of materials out of cell across cell membrane.
Exocytosis
(extracellular fluid)
(cytoplasm)
food particle
particle enclosed in vesicle
phagocytosis
vesicle containing extracellular fluid
cell
pseudopod
pinocytosis
(a)
(b)
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Animated Review of Phagocytosis, Pinocytosis and Receptor Mediated Endocytosis.
Click on Active Transport, watch the brief overview of Active Transport and then click on Endocytosis in the bar below the animation