Describe mechanisms by which proteins mediate movement of water and solutes across membranes - movement down a concentration gradient via channels or transporter proteins; active transport (primary or secondary)

- Active is movement of molecules across the cell membrane against their concentration gradient through use of energy.

- Passive is simply molecules moving down their concentration gradient.

Active vs passive transport

- Simple diffusion.

- Channels.

- Carrier proteins.

Forms of passive transport

- Movement of ions down concentration gradient through openings (not channels) in the cell membrane.

Simple diffusion

- Is facilitated diffusion.

- Proteins that act as pores in the cell membrane and allow movements of substances down their concentration gradient.

Channels in relation to passive transport

- Aquaporins.

What protein channel is the main one for water molecules?

- Another type of protein embedded in the cell membrane.

- Binds to a specific molecule and in the process changes shape to move the bound molecule from outside the cell to the inside.

- Are much slower than channel proteins.

Carrier proteins in relation to passive transport

- Primary and secondary.

What are the 2 categories of active transport?

- Transport of molecules against a concentration gradient by using ATP.

What is primary transport?

- Proteins embedded in the membrane govern passage of molecules across the cell.

- The pump moves potassium into the cell and sodium out of the cell (against their gradients).

- When the pump points into the cell it has high affinity for sodium and binds it, in the process hydrolysing ATP and changing shape.

- The change of shape means that the pump is now pointing outside of the cell and can release sodium.

- The opposite process occurs for potassium.

How does primary transport work, using the sodium/potassium pump as an example

- A molecule is moved down its electrochemical gradient, while another is moved up its electrochemical gradient.

What is secondary transport?

- One molecule is moved up its concentration gradient which generates an electrochemical gradient for the molecule of interest to move down.

- Makes use of anti porters and symporters.

How does secondary transport work?