4. Passive membrane transport. Gradients. Diffusion types – nonspecific-, facilitated- and exchange diffusion.

Membrane transport 1

Subject and importance of the membrane transport. Types of transport (classification). Free diffusion of non-charged particles - first and second Fick’s laws. The Stokes-Einstein equation.

Definition and functions of the membrane transport:

• Transport: Processes of passing through membrane of small molecules and ions. Usually it’s a highly selectable process.

Functions:

• Regulation of the cells volume
• Imports substances necessary for energy & growth in cell
• Maintains the ion gradients & transforms energy

Importance:

• Faults in transport are cause for many diseases.
• Some kind of drugs can restore the normal cells function, changing due to membrane transport.

Types of cellular transport:

PASSIVE TRANSPORT:

• Cell does not use energy
• Molecules move randomly
• Molecules spread out from an area of high concentration to an area of low concentration

There are 3 types of passive transport:

1. Diffusion
2. Facilitated diffusion - diffusion with help of transport proteins
3. Osmosis - diffusion of water

ACTIVE TRANSPORT:

• Cell does use energy
• Actively moves molecules to where they are needed
• Movement from area of low concentration to area with high concentration

There are 3 types of active transport.

1. Protein pumps
2. Endocytosis
3. Exocytosis

Fick’s 2nd law states that the change in concentration with time in a particular region is proportional to the change in the concentration gradient at that point in the system.