LABEL THE MEMBRANE… Phospholipids Cholesterol Peripheral proteins Integral proteins Cytoskeleton Cytoplasm Extracellular fluid
Most of the membrane A phospholipid bi-layer makes up most of the
membrane.
Polar heads
2 Non-polar tails
Fluid Mosaic Model
“Fluid” because the components are in constant motion, moving laterally (from side-to-side).
“Mosaic” because of the embedded proteins viewed from above.
Selectively Permeable
The phospholipid bilayer of the cell membrane allows hydrophobic molecules to pass through easily, but hydrophilic do NOT.
Materials soluble in lipids can pass easily through the cell membrane.
Selectively Permeable
Because the membrane is selectively permeable, only small molecules and larger hydrophobic molecules can pass through easily.
Examples: O2, CO2, and H2O (small)
Selectively Permeable
Ions, hydrophilic molecules larger than water, and large molecules such as proteins do NOT move through the membrane on their own.
Simple Diffusion
Requires NO energy
Molecules move from an area of HIGH concentration to an area of LOW concentration.
Diffusion Diffusion is a passive
process, which means that no energy is used to cause the molecules to move. The do so because of their own natural kinetic energy, or energy of motion.
Osmosis
Osmosis is the diffusion of water across a semipermeable membrane.
Moves from HIGH water potential (low solute) to LOW water potential (high solute)
Osmosis Water diffuses through the pores called aquaporins of
the cell membrane.
These aquaporins are specialized proteins embedded in the plasma membrane.
Movement through these protein channels DOES NOT require energy.
Cell in Isotonic Solution
CELL
10% NaCL 90% H2O
10% NaCL 90% H2O
What is the direction of water movement?
The cell is at _______________. equilibrium
ENVIRONMENT
NO NET MOVEMENT
Cell in Hypotonic Solution
CELL
10% NaCL 90% H2O
20% NaCL 80% H2O
What is the direction of water movement?
Cell in Hypertonic Solution
CELL
15% NaCL 85% H2O
5% NaCL 95% H2O
What is the direction of water movement?
ENVIRONMENT
Isotonic Solution
NO NET MOVEMENT OF H2O (equal amounts entering & leaving)
Hypotonic Solution
CYTOLYSIS
Hypertonic Solution
PLASMOLYSIS
Which environment is best?
Plants prefer hypotonic environments, while animal cells do best in isotonic environments.
Passive Transport Simple Diffusion
•Does NOT require energy
• Moves high to low concentration •Example: Oxygen or water diffusing into a cell and carbon dioxide diffusing out.
Passive Transport Facilitated diffusion
•Does NOT require energy
•Uses transport proteins to move high to low concentration •Examples: Glucose or amino acids moving from blood into a cell.
Types of Transport Proteins
• Channel proteins are embedded in the cell membrane & have a pore for materials to cross by facilitated diffusion.
• Carrier proteins can change shape to move material from one side of the membrane to the other
Facilitated Diffusion
Molecules will randomly move through the pores in Channel Proteins.
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Facilitated Diffusion Some Carrier proteins do
not extend through the membrane.
They bond and drag molecules through the lipid bilayer and release them on the opposite side.
Active Transport
•Requires energy or ATP
•Moves materials from LOW to HIGH concentration
•AGAINST concentration gradient
Active Transport • Examples: Pumping Na+
(sodium ions) out and K+ (potassium ions) in against strong concentration gradients.
• Called the Sodium/Potassium Pump
Moving the “Big Stuff”
Molecules are moved out of the cell in vesicles that fuse with the plasma membrane.
Exocytosis- moving
things out.
This is how many hormones are secreted and how nerve cells communicate with one another.
Pinocytosis • Cell forms an
invagination
• Materials dissolve in water to be brought into cell
• Called “Cell Drinking”
Receptor-Mediated Endocytosis
Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.
Phagocytosis
Used to engulf large particles such as food, bacteria, etc. into vesicles
Called “Cell Eating”