Active Transport, Transmembrane Proteins,

and Neurons

AP Biology 2006

Carrier Proteins

Exocytosis and Endocytosis

Movement of large molecules out of the cell

http://www.bbc.co.uk/education/asguru/biology/01cellbiology/05pathways/09endoexo/index.shtml

Receptor Mediated Endocytosis

LIGANDS

a ligand is an atom, ion or functional group that donates its electrons through a coordinate covalent bond to one or more central atoms or ions, usually metals. An array of such ligands around a center is termed a complex.

Ligands

Can open a gated channel Can participated in cell signalling Can participate in receptor

mediated endocytosis

LIGANDS

Ligand Gated Channels

Receptor Mediated Endocytosis

Primary Active Transport

http://www.bbc.co.uk/education/asguru/biology/01cellbiology/05pathways/08active/index.shtml

Active Transport

http://www.stolaf.edu/people/giannini/flashanimat/transport/secondary%20active%20transport.swf

ABC Transporters

Transporters are transmembrane proteins that expose a ligand-binding domain at one surface

ATP-binding domain at the other surface.The ligand-binding domain is usually restricted to a single type of molecule

Complexity of transport

ABC

ABC ABC ("ATP-Binding Cassette"). The ATP bound to its domain provides the energy to pump the ligand across the membrane. The human genome contains 48 genes for ABC transporters. Some examples:

Examples

CFTR — the cystic fibrosis transmembrane conductance regulator

TAP, the transporter associated with antigen processing.

the transporter that liver cells use to pump the salts of bile acids out into the bile.

ABC transporters that pump chemotherapeutic drugs out of cancer cells thus reducing their effectiveness. ABC transporters must have evolved early in the history of life. The ATP-binding domains in archaea, eubacteria, and eukaryotes all share a homologous structure, the ATP-binding "cassette".

Gated and NON Gated Channels

The Action Potential The action potential is electrical in nature It moves along the neuron like a wave The action potential involves highly selective and

controlled ion movement through specialized channels and pumps

The distribution of ions outside and inside of a membrane is maintained by these transmembrane proteins

Na+ is the major extracellular ion and K+ and P-

( proteins) are the major intracellular ions The outside has a positive charge in regard to the

outsideCl-

Na +

P-

K+

Ion Channels and the Action Potential• The membrane is polarized. This is

the resting potential of the membrane

• The sodium channel opens and sodium ions rush into the inside of the axon

• The potassium gates open up and potassium rushes out of the cell

• The potssium gates are slower

• This is the action potential. It produces a wave of - charge that moves down the neuron

• The sodium pumps binds three sodiums and passes them to the outside and two potassium and passes them to the inside- this is like a “ swinging door”.

• Finally the membrane returns to the resting potential

The Origin and Transmission of Neural Impulses

Neural impulses are generated by an action potential The action potential is generated when the membrane

of the neuron which has a positive charge on the outside is depolarized in a wave along its length

++++++++++++++++++++++++++++++++

----------------------------------

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++++++++++++++++++++++++++++++

-60mv

30mv

polarized

depolarized

The Wave

+++-----+++++---+++++------

The Wave

The axon

Repolarized – depolarized - polarized

Electrochemical Changes During the Action Potential

Voltage Changes during the Action Potential