1.4 Membrane Transport Flashcards
Describe vesicle formation?
ATP provides energy for a small region of a membrane to be pulled from the rest and pinched off.
How do vesicles help to increase the surface area of the plasma membrane?
Phospholipids synthesized next to rER and become inserted into rER membrane. Vesicles then bud off rER and join the plasma membrane, increasing its size.
What do vesicles carry out of the cell by exocytosis?
Excess water, polypeptides, and waste.
Define diffusion.
Process by which a substance moves from an area of higher concentration to lower concentration.
How easily do small polar molecules, ions, and small nonpolar molecules diffuse across the membrane?
Small, polar: moderately easily
Ions: not easily
Small, nonpolar: easily
Define facilitated diffusion.
Process of passive transport facilitated by integral proteins.
Describe the physical and chemical specificity of potassium pumps in axons.
Chemical: If the ions were smaller than K+, then bonds with amino acids in the pump could not form, so it couldn’t pass through. Amino acids attract K+ from surrounding H2O molecules.
Physical: Channel size prevents large items going through.
Define osmosis.
The tendency of a fluid to pass through a semipermeable membrane into a solution where the solvent concentration is higher, equalizing the overall concentrations.
What is a hypotonic solution? What occurs to plant and animal cells therein?
- Hypotonic solution: low solute concentration.
- Animal cells lyse as water flows in. Plant cells are normal.
What is an isotonic solution? What occurs to plant and animal cells therein?
- Isotonic soluton: equal solute to water concentration.
- Animal cells normal. Plant cells are flaccid as water leaves and enters in equal amounts.
What is a hypertonic solution? What occurs to plant and animal cells therein?
- Hypertonic solution: high solute concentration
- Animal cell is shriveled as H2O leaves. Plant cell is plasmolyzed as H2O leaves.
Why is ideal water balance different between plant and animal cells?
Plant cells’ cell walls resist osmotic pressure from being in a hypotonic solution those those without cell walls.
What is needed for active transport?
ATP (energy).
Outline how the Na+/K+ protein pump works.
- Pump opens to the inside of the axon; 3 Na+ enter and attach to binding sites.
- ATP transfers a phosphate group from itself to the pump, causing the pump to close.
- Pump opens to outside axon and 3 Na+ are released.
- 2 K+ ions from outside enter and attach to binding sites.
- Pump opens to inside and 2 K+ ions enter.
