Transport across cell membrane Dr Farzana Salman.

Transport of substances through cell membrane Lipid bilayer Protein molecules

Transport through the cell membrane either directly through the lipid bilayer or through the proteins occur by one of the following basic process. Diffusion Active transport.

Diffusion Simple diffusion Facilitated diffusion

Simple Diffusion Simple diffusion : kinetic movement of molecules or ions occur through a membrane opening or through intermolecular spaces without any interaction with carrier proteins in the membrane.

Simple diffusion The rate of simple diffusion is determined by 1. The amount of substance available 2. The velocity of kinetic motion. 3. The number and sizes of openings in the membrane

SIMPLE DIFFUSION Diffusion of lipid soluble substances through the lipid bilayer Diffusion of water and other lipid insoluble molecules through protein pores/channels

Diffusion of lipid soluble substances through the interstices of lipid bilayer Oxygen Carbon dioxide Nitrogen Alcohol.

Leak channels. Na-K leak channels Diffusion of water and other lipid insoluble molecules through protein channels. Protein pores/tubes Aquaporins Protein channels Leak channels. Na-K leak channels Voltage gated channels. Na- K gated channels Ligand gated channels. Acetylcholine gated channels

Voltage Gated Sodium Channels

Facilitated Diffusion Substance diffuses through the membrane using a specific carrier protein . Rate of diffusion approaches a maximum Vmax Glucose transportaters (GLUT 4)

Factors that effect the net rate of diffusion 1.Concentration difference across a membrane. 2. Nernst potential. 3. Pressure difference across the membrane

ACTIVE TRANSPORT

Active transport can move a solute against its electrochemical gradient Uphill movement Requires energy

Primary active transport Transport that is coupled directly to an energy source. Secondary active transport Transport that is coupled indirectly to an energy source. Carrier Proteins

Primary Active Transport Sodium Potassium Calcium Hydrogen

Sodium Potassium ATPase Pump

α subunit α 1 ---- most cell membrane α 2 ---- Muscle ,Heart, Brain, Adipose tissue α 3 ----- Heart , Brain. β subunit β 1--- Widely distributed. β 2--- Glycolytic fast twitch muscle. β 3

Na-K ATPase Pump Functions 1. Acts as an enzyme 2. Electrogenic 3. Maintains cell volume.

Calcium Pump

Hydrogen ATPase Pump

Hydrogen Pump Gartric glands of the stomach Late distal tubules and cortical collecting ducts of the kidney

Secondary Active Transport In secondary active transport the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the two sides of a cell membrane created originally by primary active transport.

Co Transport Sodium Glucose Co transport Sodium Amino acid Co transport

Sodium Glucose Cotransport

Counter Transport Sodium calcium counter transport Sodium Hydrogen counter transport