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24 Cards in this Set

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specificity
Receptors show _________ for the messenger

They generally bind only one messenger or a class of messengers.
messenger
A single _________ cell can often bind to more than one type of receptor, and these receptors may have different affinities for the messenger.
target
A single ______ cell may have receptors for more than one type of messenger.
affinity
the strength of the binding btwn a messenger and its receptor
Up regulation
an increase in # of receptors compared to "normal" conditions, occurs when cells are exposed to low messenger concentration for a prolonged period.

become more responsive
Down regulation
a decrease in the # of receptors, occurs when messenger conc. are higher than normal for a prolonged period.

become less responsive
agonists
Ligands that bind to receptors and produce a biological response
antagonists
Ligands that bind to receptors but do NOT produce a response.

May actually compete with agonist for the receptor, decreasing the likelihood that the binding of agonist to receptor will occur and bring about a response.
Ligand-gated channels
Ions channels that open or close in response to the binding of a chemical to a receptor or to the channel
Channel-linked receptors
a type of ligand-gated channel in which the ligand is a messenger that binds to a receptor.
Effects of the target cell in channel-linked receptors
1. Ions entering and leaving can change the electrical properties of the cell

2. Entering ions can interact with proteins inside the cell to induce a response such as muscle contraction, secretion, change in metabolism, or altered transport of a substance.
Second messenger
Calcium enters cell through open channel as a _______ ________ which activates enzymes. Enzymes acts on other proteins.
Will eventually change cell function.
Calcium
________ is an internal signal.
Enzyme-linked receptor
Enzyme molecule has a binding site. When enzyme binds it is active, and when enzyme does NOT bind it is inactive.

When enzyme binds it is active, produces ATP through phosphoralation, and product eventually changes cell function.
G proteins
Involved in transducing chemical signals to response of cells.
Calcium
cAMP
________ and _____ are secondary messengers that act as internal signals.
glial cells
Cells of the central nervous system and peripheral nervous system that support and protect neurons; also called neuroglia.
nervous system
Direct cell-to-cell communication in the ______ ______ generally involves the opening and closing of ion channels, which is very fast and a short duration.

Signals travel quickly and short duration and ideal for controling movement and monitoring the world around us.
endocrine system
hormones
The ________ system communicates through chemical receptors called hormones, which travel through bloodstream to all cells in body.
________ diffuse into blood

generally communicate by altering protein synthesis or activating G proteins, processes are slower than nervous system.
adenylate cyclase
G proteins bind to and active this enzyme

Catalyzes the conversion of ATP to cAMP.
DAG (diacylglycerol)
Membrane phospholipid formed after hydrolysis of PIP2. Functions as a second messenger that activates protein kinase C.
Inositol triphosphate (IP3)
A second messenger produced by hydrolysis of PIP2. It enters the cytoplasm to open calcium channels in endoplasmic reticulum.
Phosphatidyl inositol biphosphate (PIP2)
A plasma membrane phospholipid. Hydrolysis produces two molecules, IP3 and DAG, that act as second messengers.
cGMP
a product of an enzyme-linked receptor, guanlynate cyclase which is commonly associated with G proteins.

A second messenger that is similar to cAMP but it activates protein kinase G.