Chapter 12 (Exam 4) Powerpoint Summarized - Molec Cell Bio

Small nonpolar and small uncharged polar molecules in biological membranes

diffuse slowly

Large polar and charged molecules in biological membranes

require transport proteins

In passive transport,

molecules move down their gradient

• no energy is required

In active transport,

molecules move against their gradient

• requires energy

Na+/K+ pump uses

ATP to move 3 Na+ out and 2 K+ in

• maintains electrochemical gradient

Ca2+ pump uses

ATP to move Ca2+ into the ER or sarcoplasmic reticulum (smooth ER)

• maintains low cytosolic Ca2+

Ion channelss are selective for specific ions and are regulated by

• mechanically gated channels

• ligand-gated channels

• voltage gated channels

K+ leak channels contribute to

resting membrane potential

Depolarization opens

voltage-gated NA+ channels → influx of Na+

• then triggers voltage-gated K+ channels → restoring resting potential

• propagation down the axon

Action potentials trigger

Ca2+ influx in presynaptic cells

• causes neurotransmitter release into the synapase