Physio Section 2

Fedorov P2

Ligand

any molecule (Chemical Messengers) that is bound to a protein; typically reversible

binding sites; multiple ligands

protein can have many ____________ for _____________

change the conformation of the protein

Binding of a ligand to a protein will often ________________.

affinity

depends on strength of ligand-protein binding

saturation

all of the binding sites are occupied

competition

more than one ligand can bind one site

specificity

The first messenger binding site has a particular shape into which only certain molecules fit.

saturation

the degree to which the receptors on a cell are occupied by a messenger. The more receptors are occupied by a messenger the stronger the cellular response

affinity

the strength with which a chemical messenger binds to its receptor.

competition

Different molecules with similar structures can compete for the same receptor-binding site.

agonist

A molecule that binds to a receptor and triggers a normal response, “mimics”

antagonist

A molecule that binds to a receptor but does not trigger a response, “blockers”

down-regulation

high messenger concentration over time decreases receptor number; cells develop decreased sensitivity

up-regulation

low messenger concentration over time increases receptor number; cells develop increased sensitivity

plasma membrane

most receptors are located in the _____________

different

The same type of receptor can produce very ___________ responses in different cell types.

receptors that function as ion channels

When a first messenger attaches to the receptor, the ion channel is opened. Ions will move in and out and this will change the electrical potential of the membrane and intracellular concentrations of ions

receptors that function as enzymes

When the first messenger binds to the receptor the enzyme portion of the protein, located inside the cell, is Activated. Will lead to changes in gene expression, cell growth, cell proliferation, or differentiation

Receptors that Interact with

Cytoplasmic Enzymes

When a first messenger attaches to the receptor, a conformational change in the receptor leads to activation of the cytoplasmic enzyme. Will lead to changes in gene expression, cell proliferation, or immune response

receptors that interact with G-Proteins

the receptor (membrane protein) is NOT a channel or an enzyme. The receptor is linked through G-proteins to effector proteins such as ion channels or enzymes.

G-Protein Coupled Receptors

1st messenger binds to the receptor and produces a conformational change; part of the G-protein dissociates, diffuses along the inner surface of the PM and binds to an effector protein; effector protein becomes activated and produces a cellular response

effector proteins; second messengers

GPCRs activate _____________ and _____________ such as cAMP

phosphodiesterase (PDE)

cAMP amplifies signals and is regulated by _____________.