1.6 transport across the membrane

Question 1

what DOES NOT get through the lipid bilayer easily?

Answer 1

• polar
• charged (ions in aqueous solution are usually surrounded by water molecules and are larger – hydration shells)
• large molecules

usually transported by proteins in the membrane

Question 2

what DOES get through the lipid bilayer easily

Answer 2

small, non polar molecules
uncharged polar molecules

Question 3

things to consider for question about membrane permeability

Answer 3

small vs large
polar vs nonpolar
charged vs uncharged

Question 4

passive transport

Answer 4

• diffusion
• good for things small and uncharged
• transport along a concentration gradient
• does not require input of energy

has two types:
- simple diffusion
- facilitated diffusion

Question 5

simple diffusion

Answer 5

type of passive transport
diffuses through lipid bilayer

Question 6

facilitated diffusion

Answer 6

when a molecule moves by diffusion through a membrane protein and bypasses the lipid bilayer

Question 7

facilitated diffusion via CHANNEL proteins

Answer 7

provides an opening between the inside and outside of the cell through which certain molecules can pass, depdning on their shape and charge

• channel can be “open” or “gated” (open/close due to some signal)
• molecules can diffuse through the channel
• usually selective for a specific type of molecule
• molecules have to interact with protein channel for the molecule to be transported
• provides a hydrophilic passageway
• transport through a channel usually occurs at a faster rate than carrier proteins

Question 8

facilitated diffusion via CARRIER proteins

Answer 8

• gated
• transport a SPECIFIC type of molecule (more specific than channels)
• open and closed formation
• protein undergoes a shape change (conformational changes) to open and close the protein

binds to and then transports specific molecules
§ Exist in two conformations
□ Open to one side of the cell
□ Open to the other side of the cell

Question 9

primary active transport

Answer 9

energy is required to directly move a molecule from one side of the membrane (usually against a concentration gradient)

Question 10

secondary active transport

Answer 10

• energy still required, but is used to build up a concentration of a DIFFERENT MOLECULE
• diffusion of that molecule along its electrochemical gradient is then used to power the movement of the desired molecule
• use energy to move A to create electrochemical gradient that NATURALLY moves B

Question 11

Electrical gradient

Answer 11

difference in charge

Question 12

Electrochemical gradient

Answer 12

gradient in both charge and chemical components