Active Transport with the Sodium Potassium Pump

Review

• Amphipathic molecules:– Hydrophobic region and hydrophilic region• Example: Phospholipids and Membrane Proteins

• Molecules that can pass directly through membrane

• Hydrophobic molecules (non-polar): Dissolve in the bilayer• Glucose can transport easily (small molecule)

Cell Membrane Voltage

• All cells have voltage• Cytoplasm of cell is

more negative than the outside of the cell– Unequal distribution of

anions and cations

Membrane potential

• Cellular voltage = Membrane potential– Ranges from -50 mv to -200 mv

• Remember opposites attract!– Cations want to move into the cell since it is more

negative

Electrochemical gradient

• 2 forces drive the diffusion of ions across the membrane!!– The concentration gradient (chemical gradient)– Electric force

Creates an ELECTROCHEMICAL gradient

Sodium Potassium Pump

Sodium Potassium Pump

• Remember the inside of the cell is more negative– If left to nature cations would move into the cell,

messing up this membrane potential– Sodium potassium pump maintains membrane

potential using an ATPase

Steps1. 3 sodium ions from inside the cell bind to the

pump2. ATP is used to change the shape of the

protein3. Sodium is released inside the cell4. 2 potassium ions bond to the pump (changed

shape form) and the pump goes back to original shape

5. 2 potassium ions are released inside the cell

http://www.ibiblio.org/virtualcell/textbook/chapter3/movies/pro6.gif

Signal Transduction Pathway

Chapter 11

Yeast Sex

Direct Signaling

• Cell junctions (signals travel between cells)• Cell to Cell recognition

Local regulation• Cells in the vicinity undergo local regulation• Paracrine signaling: – Growth factors stimulate nearby cells to grow and

multiply– Many cells receive and respond to growth factors

at the same time

Local regulation

• Synaptic signaling– Electric signal triggers secretion of a

neurotransmitter (chemical signal) which diffuses across the synapse

– Neurotransmitter stimulates target cell

Long distance signaling

• Hormonal signaling– Specialized endocrine cells secrete hormones,

which travel through blood stream (or other fluids)

Signal Transduction Pathway

• 3 steps– Reception: signal molecule meets receptor

molecule– Transduction: converts signal so that a response

can take place– Response: a cellular response takes place