Chapter 11

Question 1

cadherin

Answer 1

Any of a class of cell-surface proteins involved in selective cell–cell adhesion. Important for coordinating movements of cells and the establishment of tissues during embryological development.

Question 2

collagen

Answer 2

A fibrous, pliable, cable-like glycoprotein that is a major component of the extracellular matrix of animal cells. Various subtypes differ in their tissue distribution, some of which are assembled into large fibrils in the extracellular space.

Question 3

crosstalk

Answer 3

Interactions among signaling pathways that modify a cellular response.

Question 4

desmosome

Answer 4

A type of cell–cell attachment structure, consisting of cadherin proteins, that is anchored to intermediate filaments. Serves to link the cytoskeletons of adjacent animal cells and form strong cell–cell attachments throughout a tissue. Compare with gap junction and tight junction.

Question 5

expansins

Answer 5

A class of plant proteins that break hydrogen bonds between components in the primary cell wall to allow it to expand for cell growth.

Question 6

extracellular matrix (ECM)

Answer 6

A complex meshwork in which animal cells are embedded, consisting of proteins (e.g., collagen, proteoglycan, laminin) and polysaccharides produced by the cells.

Question 7

G protein

Answer 7

Any of various proteins that are activated by binding to guanosine triphosphate (GTP) and inactivated when GTP is hydrolyzed to GDP. In G-protein-coupled receptors, signal binding directly triggers the activation of a G protein, leading to production of a second messenger or initiation of a phosphorylation cascade.

Question 8

gap junction

Answer 8

A type of cell–cell attachment structure that directly connects the cytosolic components of adjacent animal cells, allowing passage of water, ions, and small molecules between the cells. Compare with desmosome and tight junction.

Question 9

integrin

Answer 9

Any of a class of cell-surface proteins that bind to laminins and other proteins in the extracellular matrix, thus holding cells in place.

Question 10

laminins

Answer 10

An abundant protein in the extracellular matrix that binds to other ECM components and to integrins in plasma membranes; helps anchor cells in place. Predominantly found in the basal lamina; many subtypes function in different tissues.

Question 11

microfibril

Answer 11

Bundled strands of cellulose that serve as the fibrous component in plant cell walls.

Question 12

mitogen-activated protein kinases (MAPK)

Answer 12

Enzymes that are involved in signal transduction pathways that often lead to the induction of cell replication. Different types are organized in a series, where one kinase activates another via phosphorylation. See also phosphorylation cascade.

Question 13

pectin

Answer 13

A gelatinous polysaccharide found in the primary cell wall of plant cells. Attracts and holds water, forming a gel that resists compression forces and helps keep the cell wall moist.

Question 14

phosphatase

Answer 14

An enzyme that removes phosphate groups from proteins or other molecules. Phosphatases are often used in the inactivation of signaling pathways that involve the phosphorylation and activation of proteins.

Question 15

phosphorylation cascade

Answer 15

A series of enzyme- catalyzed phosphorylation reactions commonly used in signal transduction pathways to amplify and convey a signal inward from the plasma membrane.

Question 16

primary cell wall

Answer 16

The outermost layer of a plant cell wall, made of cellulose fibers and gelatinous polysaccharides, that defines the shape of the cell and withstands the turgor pressure of the plasma membrane.

Question 17

protein kinase

Answer 17

An enzyme that catalyzes the addition of a phosphate group to another protein, typically activating or inactivating the substrate protein.

Question 18

proteoglycan

Answer 18

A type of highly glycosylated protein found in the extracellular matrix of animal cells that attracts and holds water, forming a gel that resists compression forces.

Question 19

quorum sensing

Answer 19

Cell–cell signaling in unicellular organisms, in which cells of the same species communicate via chemical signals. It is often observed that cell activity changes dramatically when the population reaches a threshold size, or quorum.

Question 20

Ras protein

Answer 20

A type of G protein that is activated by enzyme-linked cell-surface receptors, including receptor tyrosine kinases. Activated Ras then initiates a phosphorylation cascade, culminating in a cell response.

Question 21

receptor tyrosine kinase (RTK)

Answer 21

Any of a class of enzyme-linked cell-surface signal receptors that undergo phosphorylation after binding a signaling molecule. The activated, phosphorylated receptor then triggers a signal transduction pathway inside the cell.

Question 22

second messenger

Answer 22

A nonprotein signaling molecule produced or activated inside a cell in response to stimulation at the cell surface. Commonly used to relay the message of a hormone or other extracellular signaling molecule.

Question 23

selective adhesion

Answer 23

The tendency of cells of one tissue type to adhere to other cells of the same type.

Question 24

signal receptor

Answer 24

Any cellular protein that binds to a particular signaling molecule (e.g., a hormone or neurotransmitter) and triggers a response by the cell. Receptors for lipid-insoluble signals are transmembrane proteins in the plasma membrane; those for many lipid-soluble signals (e.g., steroid hormones) are located inside the cell.

Question 25

tight junction

Answer 25

A type of cell–cell attachment structure that links the plasma membranes of adjacent animal cells, forming a barrier that restricts movement of substances in the space between the cells. Most abundant in epithelia (e.g., the intestinal lining). Compare with desmosome and gap junction.