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