Chapter 7 - Cell Communication and Multicellularity

signal transduction pathway

The series of biochemical steps whereby a stimulus to a cell (such as a hormone or neurotransmitter binding to a receptor) is translated into a response of the cell.

autocrine

a chemical signal that binds to and affects the cell that makes it

juxtacrine

A mode of cell communication where the cell producing a signal is in contact with the cell bearing the receptor for that signal

paracrine

Pertaining to a chemical signal, such as a hormone, that acts locally, near the site of its secretion.

hormones

a chemical signal produced in minute amounts at one site in a multicellular organism and transported to another site where it acts on target cells

signals that travel through the circulatory systems of animals or the vascular systems of plants are generally called _____

hormones

only cells with the appropriate receptors can...

respond to a signal

crosstalk

interactions between different signal transduction pathways

a _____ protein recognizes its signal very specifically, in much the same way that a membrane transport protein recognizes and binds to the substance it transports

receptor

ligand

Any molecule that binds to a receptor site of another (usually larger) molecule.

a _____ is a specific chemical signal molecule that fits into a 3D site on its protein receptor

ligand

dissociation contant (kD)

a type of equilibrium constant measuring the tendency of 2 substances that are bound together to separate into the 2 smaller components. In cell signaling, the 2 substances are a ligand and a receptor

_____ is a measure of the affinity of the receptor for its ligand

kD, the dissociation constant

agonist

a chemical substance that elicits a specific response in a cell or tissue

antagonist

a biochemical substance that blocks the normal action of another biochemical substance

types of receptors:

- membrane receptors

- intracellular receptors

ion channels

An integral membrane protein that allows ions to diffuse across the membrane in which it is embedded.

protein kinase

An enzyme that catalyzes the addition of a phosphate group from ATP to a target protein.

G protein-coupled receptors

A class of receptors that change configuration upon ligand binding such that a G protein binding site is exposed on the cytoplasmic domain of the receptor, initiating a signal transduction pathway.

G protein

A membrane protein involved in signal transduction; characterized by binding GDP or GTP

effector protein

In cell signaling, a protein responsible for the cellular response to a signal transduction pathway.

_____ is known as a second messenger in the signal transduction pathway involved in the "fight or flight" response

cAMP

A key property of signal transduction pathways is that one signal molecule binding to a receptor protein in the cell membrane...

can result in several thousand events at the end of the pathway

what advantage is gained by having so many steps in one signal transduction pathway?

greater amplification of the signal

intracellular receptor

a receptor that binds its ligand inside the cell. an example is the estrogen receptor in mammals

_____ are located inside the cell and respond to physical signals such as light or chemical signals that can diffuse across the cell membrane

intracellular receptors

second messenger

A compound, such as cAMP, that is released within a target cell after a hormone (the first messenger) has bound to a surface receptor on a cell; the second messenger triggers further reactions within the cell.

_____ can diffuse throughout the cytoplasm and mediate further steps in pathways

second messengers

protein kinase cascade

a series of reactions in response to a molecular signal, in which a series of protein kinases activate one another in sequence, amplifying the signal at each step

protein kinase cascades are useful signal transducers for 4 reasons:

- the signal is amplified at each step

- info from a signal that originally arrived at the cell membrane is communicated to the nucleus

- the multitude of steps provides some specificity to the process

- different target proteins at each step in the cascade can provide variation in the response

what is a key property of the receptor protein in a signal transduction pathway?

the receptor's cytoplasmic domain undergoes a conformational change when the signal molecules binds to its extracellular domain

cAMP (cyclic AMP)

A compound formed from ATP that acts as a second messenger.

phosphatidyl inositol-biphosphate (PIP2)

a phospholipid in the cell membrane that is involved in cell signaling after a ligand binds to a nearby receptor

diacylglycerol (DAG)

In hormone action, the second messenger produced by hydrolytic removal of the head group of certain phospholipids.

PIP2 has a hydrophobic portion embedded in the cell membrane: 2 fatty acid tails attached to a molecule of glycerol, which together form _____

diacylglycerol, or DAG

inositol triphosphate (IP3)

An intracellular second messenger derived from membrane phospholipids.

the hydrophilic portion of PIP2 is _____, which projects into the cytoplasm

inositol triphosphate (IP3)

gap junction

A 2.7-nanometer gap between plasma membranes of two animal cells, spanned by protein channels. Gap junctions allow chemical substances or electrical signals to pass from cell to cell.

_____ are channels between adjacent cells that occur in many animals, occupying up to 25% of the area of the cell membrane

gap junctions

connexon

In a gap junction, a protein channel linking adjacent animal cells.

plasmodesmata

cytoplasmic strands connecting two adjacent plant cells

instead of gap junctions, plants have _____, which are membrane-lined tunnels that traverse the thick cell walls separating plant cells from one another

plasmodesmata

desmotubule

A membrane extension connecting the endoplasmic reticulum of two plant cells that traverses the plasmodesma.

PIP2 is a phospholipid in cell membranes that produces two lipid-derived _______ when hydrolyzed by phospholipase C.

second messengers

what is the correct order of steps in a generalized signal transduction pathway?

signal molecule binds to receptor, molecules within cell transduce signal, cell responds

the membrane-lined tunnels called plasmodesmata that connect adjacent plant cells...

allow as much flow between cells as do gap junctions in animal cells

protein kinase receptors phosphorylate themselves and/or other proteins when activated, resulting in a...

change in shape and function of the proteins

gap junctions allow passage of ions and small proteins from one cell to the next through small channels called _____

connexons