Transport Through Membranes Flashcards
What is simple diffusion
It’s a passive process which no ATP or energy is needed. It occurs naturally in all liquids and gasses.
The gaps between phospholipids are small and the centre of the bilayer is hydrophobic.
For simple diffusion to occur the phospholipid bilayer particles must be small, uncharged
Large molecules which are polar cannot move by simple diffusion
What does the rate of diffusion depend on in membranes
Concentration gradient- the higher the conc gradient the faster diffusion
Distance of travel- shorter the distance the faster the rate
Temperature - increase in temperature Increases molecular kinetic energy so increases rate
Size of the molecule- smaller molecules diffuse faster And pass through phospholipids easier
Surface area- the more surface area the increased rate
Lipid solubility- can diffuse easily
What is facilitated diffusion
Diffusion of particles across membrane using protein carriers or channels without need of ATP energy
- passive process
Down a concentration gradient
What is a channel protein?
Pores linked with polar groups to make them hydrophilic
Each channel protein is specific to one type of ion
Protein changes shape
What is carrier protein?
Large molecules attach to carrier proteins
The proteins change shape and molecule is released onto the opposite side of the membrane
ATP is not required when used in facilitated diffusion as its going down a conc gradient
What is active transport?
Movement of molecules against a concentration gradient using ATP and protein carriers
This is a selective process
The ion or molecule being moved binds to complementary receptor sites on the carrier protein.
ATP binds to the protein and splits releasing pi causing protein to change shape releasing the ion on the other side.
When the pi is released from protein it goes to its original shape.
Energy from atp is needed.
Anything which inhibits respiration stops active transport.
What is osmosis
Movement of water from a high water potential to a low water potential across a partially permeable membrane
What’s an aquaporin
A protein channel that water moves through
Or it moves without it as the molecules are small
What is water potential
Tendency of water to leave or enter a system
The greater the number of free water molecules the greater the water potential
Water has then highest wp of 0
Describe the different situations of water potential
Isotonic - same wp outside and inside cell
Hypotonic - more wp outside the cell so water moves inwards - bursts
Hypertonic - more water potential inside cell so the water moves outward - shrivelled
How does co-transport work?
Sodium ions are pumped out of the epithelial cell by active transport into the blood stream
This creates a lower conc of sodium inside the cell
Sodium then can enter the epithelial cell from the lumen down a concentration gradient but with glucose - co transport
Glucose is now at a high concentration in the cell and so exits into the capillary by facilitated diffusion down a concentration gradient.
What indirectly powers the movement of glucose into the epithelial cell
The sodium ion concentration gradient
