Ch. 7- Plasma Membrane
*Transport*
Selectively permeable (or semi-permeable)
Materials move based on:
Size
Polarity
Remember: Like dissolves like!
Relation to the membrane?
Membrane Transport
Membrane review!
Don’t forget… it’s fluid!
Cholesterol
Kinked tails
Hydrophobic core of membrane:
Hydrophobic molecules cross easily
Ex: CO2, O2 <-- why?
Very small, hydrophilic molecules pass between phospholipids
Ex. H2O
Large, hydrophilic molecules must use protein channels
Ex. glucose
Membrane Transport
Comparing Non polar & Polar Molecules
Cell does not use energy
Diffusion
Movement of molecules down concentration gradient (high to low)
Goal is equilibrium
Ex. Oxygen moving into cell during respiration
Passive Transport
Osmosis
Diffusion of water across semipermeable membrane
When comparing two solutions:
Hypertonic = Higher concentration of solutes, less H2O
Isotonic= Equal concentration of solutes
Hypotonic= Lower concentration of solutes, more H2O
Water moves from hypo- to hypertonic solution
Passive Transport
Solution Basics
Osmosis in Red Blood Cells
Hypertonic
Plasmolysis
Osmosis in Plant Cells
Isotonic
Flaccid
*Desire hypotonic environment= turgid
Support = turgor pressure
Facilitated Diffusion
Diffusion of polar molecules and ions with help of transport proteins
Movement is still going down concentration gradient
Transport proteins are similar to enzymes:
Specialized
Can be saturated
Can be inhibited
Passive Transport
Facilitated Diffusion
Gated channels= Transport proteins that must be stimulated to open or close
Facilitated Diffusion- Gated Channels
Ultimate Goal
Ultimate goal of all passive transport is to achieve EQUILIBRIUM
Dynamic; not static
Substances are always moving, but there should be no net (overall) change
Movement of molecules against concentration gradient (low to high)
Cell must use energy (ATP)
Active Transport
Sodium-Potassium Pump
Cells have less Na+ and more K+ than surrounding environment
How? Proteins use ATP to pump Na+ out and K+ in
3 Na+ out
2 K+ in
Process maintains electrical charge across membrane --> membrane potential
cytoplasm has a (-) charge
Active Transport
Phosphorylation
How does ATP actually drive this process?
Phosphorylation!
Remember: ATP —> ADP + P
Phosphorylation
Active Transport- Bulk
Exocytosis (Out)
Example: Secreting insulin
Endocytosis (In)
Phagocytosis: Particles (eating)
Pinocytosis: Fluid (drinking)
Receptor-mediated endocytosis: Absorption of molecules based upon receptors in membrane
Exocytosis
Endocytosis
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