CH 6: E. Passive Transport, F. Active Transport

Osmosis

the diffusion (spread) of water past a selectively permeable membrane

from the region with lower solute concentration to region with higher solute concentration

How does Osmosis occur?

when there is an unequal concentration of solutes across a membrane (but solute cannot pass to diffuse) the water will move across membrane to where the higher concentration is and spread out the solute so its less concentrated

How does water permeate the membrane?

water though smaller its polar and passes through the membrane through aquaporins (small pores in membrane)

Tonicity

the ability for cell to lose or gain water

types:

isotonic

hypertonic

hypotonic

isotonic

when two solutions are compared and they both have an equal concentration of solutes

hypertonic

there’s a higher concentration of solute in one solution vs another

hypotonic

there is a lower concentration of solute in one solution compared to another

What happens to the intercellular environment of a cell without a cell wall when placed in a isotonic solution?

(compared to cytoplasm)

since the cytoplasm and the solution have the same concentration of solutes, the cell net water movement stays even throughout the mixture

What happens to the intercellular environment of a cell without a cell wall when placed in a hypotonic solution?

(compared to cytoplasm)

because there is a lower concentration of solute in the solution than the cell. water moves inside the cell to even out its higher solute concentration (cell lyses)

What happens to the intercellular environment of a cell without a cell wall when placed in a hypertonic solution?

(compared to cytoplasm)

because the solution has a higher concentration of solute, the cell loses water, as it moves outside of the cell to balance out the solute (cell crenates)

Types of water balance in cell walls:

Turgid

Flaccid

Plasmolyzed

What causes Turgid cell walls?

when the water moves into the cell (cos’ hypotonic solution) creating beneficial pressure in cell wall

(good for plant growth so ideal)

What causes flaccid cell walls?

when water moves in and out of the cell wall with no net difference since there’s the same amount of solute in the plant and the soil

What causes Plasmolyzed cell walls?

When area surround cell is dry, more concentrated with solute, the water in the cell walls moves there, causing the plasma membrane to shrink away from cell wall

Active transport

when proteins in the membrane move solutes against its concentration gradient using ATP energy

its important because it allows cells to move solutes in a concentration gradient that differs from its environment

types: primary and secondary

Primary active transport

When the sodium Potassium pump (Na+ K+) consumes ATP energy to let out Na and in let K

1. unbound: protein has 3 binding sites inside that attracts sodium ions from inside of the cell

2. after sodium binds, atp molecules takes off one of its phosphate groups and it interacts with the protein, releasing energy (phosphorelation)

3. this causes protein to change its shape (closing its binding entrance and opening a exit out the cell.

4. After this, potassium from outside the cell is attached to bind in the protein

5. phosphate group is then removed which changes shape of protein, back to original form

   pushing K inside the cell

(3 + out, 2 + in, making outside of cell more postive and inside more negative - electrochemical gradient

Phosphorylation (active transport)

when phosphate group of nearby ATP molecule is removed and attaches to membrane protein (binded with Na), releasing energy that changes proteins shape (for launching Na out)

electrochemical gradient (active transport)

the overall change in charge in which outside of cell becomes more positive and inside more negative as a result of 3+ leaving (Na) and 2+ entering (K).

Secondary active transport

when molecules can be transported in/out the cell due to the electrochemical gradient created from active transport

How does Secondary active transport happen?

Since the charge outside the cell has become more positive, and inside has become more negative

the + molecules want to come back in and make inside less -

so protons and ions are drawn in and out to balance charges, their transportation powered by the electrochemical gradient rather than ATP energy

and when this happens other cotransport proteins piggyback off this momentum to transport other molecules